SB 
 
 751 
 
 UC-NRLF 
 
 B 3 fl^S 113 
 
UNITED STATES DEPARTMENT OF AGRICULTURE 
 BUREAU OF PLANT INDUSTRY 
 
 Office of Cotton, Truck, and Forage Crop Disease Investigations 
 Washington, D. C. 
 
 pb . 
 
 
 HANDBOOK 
 OF THE DISEASES OF VEGETABLES 
 
 OCCURRING UNDER MARKET, 
 STORAGE, AND TRANSIT CONDITIONS 
 
 By 
 
 GEORGE K. RELINK and MAX W. GARDNER 
 Prepared under the direction of W. A. ORTON and W. M. SCOTT 
 
 Preliminary Edition 
 
 Printed for the nsa of the Food Products Inspectors of the Bureau oi Markets 
 Not available to the public 
 
 May 24, 1919 
 
A 
 
 a 
 s 1 
 
 
 
 a 
 
 O 
 
 d- 
 CD 
 
 9 
 
 .6 
 
 d- 
 O 
 
 c+ 
 O 
 P 
 
 Ct 
 
 I 
 
 g 
 
 O 
 
 cl- 
 ef 
 CD 
 
 ca 
 
 CD 
 
 o 1 
 
 CD 
 
 refe 
 
 H> 
 
 i 
 
 ct- Q CD 
 
 I-** p 
 
 O M H 
 
 *< 
 
 ct- 
 
 . - 
 
 t>0 Q 
 
 pub 
 
 cat 
 
 J 
 I 
 
 0> 
 
 o 
 
 CO 
 
 3 a I I 
 
 H 3 C3* H 
 
 CD P. P. 
 
 g ? 
 
 ct- 
 cf- 
 
 CD ^ 
 
 ** S* 
 
 p 
 
 ct- 
 CD 
 
 ct- 
 O 
 
 8, 
 
 CO 
 
 
 t? 
 
 O 
 
 O 
 CO 
 CO 
 
 o 
 
 St 
 
 W 
 
 V 
 
 S & 
 
 CD 
 
 P*. 
 
 CO 
 CD 
 
 H. o 
 
 V. 
 
 13* 
 
 *"O 
 
 1 ct- 
 
 3 
 
 C^ C3* 
 
 .^ ^ 
 
 O 
 
 9 
 p 
 
 e 
 
 g 
 
 CO 
 d- 
 O 
 
 I 
 
 o 
 
 ^ 
 
 o 
 ST & H. 
 
 0* 
 O 
 
 o 
 
 H 
 
 
 
 " 
 
 5 
 
 I/ 
 
 
 ^ 
 
 <1 
 
 et 
 
 - 
 
 H 
 
 
 
 
 O 
 O 
 
 CD 
 
AGRIC. 
 LIBRARY 
 
 HANDBOOK OF THE DISEASES OF VEGETABLES 
 
 OCCURRING UNDER MARKET, STORAGE 
 
 AND TRANSIT CONDITIONS 
 
 By GEORGE K. K. LINK and MAX W. GARDNER. Prepared under 
 the direction of W. A. ORTON and W. M. SCOTT. 1 
 
 PREFACE 
 
 This handbook is designed primarily to aid the inspectors 
 of the Bureau of Markets in the detection and identification 
 of plant diseases as they occur in vegetables under transit, 
 storage, and market conditions. 
 
 The entire inspection service and the survey and study of 
 vegetable crop diseases under transit and market conditions, 
 were begun but little more than a year ago, consequently 
 this handbook, an outgrowth of that survey and study, is 
 necessarily incomplete. The text and illustrations are the 
 property of the United States Department of Agriculture, 
 and are not to be used in any published form whatsoever. 
 
 The description of the signs, symptoms, or effects of each 
 plant disease is followed by a statement of the geographic 
 distribution and the seasonal or climatic relations of the 
 disease so far as they are known, since some diseases occur 
 only in certain districts and often only under certain con- 
 ditions. 
 
 A statement is made as to the time and place of incep- 
 tion, development, and spread of the disease. This is 
 especially important from a market point of view. For 
 example, in placing the responsibility for the poor condition 
 of a shipment caused by bacteria or fungi, it is essential to 
 bear in mind that some diseases are field infections and do 
 not develop nor spread in transit or storage ; that others are 
 field infections which develop or progress but do not spread 
 ih transit or storage ; that others are field infections which 
 develop and spread under transit and storage conditions; 
 and finally that a number are transit and storage infections 
 of stock perfectly sound when harvested. 
 
 It is fully realized that at present not all decay can be 
 referred to clearly defined causes. However, by specifying 
 whenever possible the disease responsible for the decay or 
 defect in a consignment, the inspector can further the con- 
 
 1 Dr. V. B. Stewart was consulted freely in the preparation of the text. In addition, 
 the following men were consulted with reference to special portions as enumerated 
 below: Beans, Mr. W. W. Gilbert and Mr. G. A. Meckstroth; cabbage and other cruci- 
 fers, Dr. L. L. Barter and Dr. L. O. Kunkel; celery, Dr. I. C. Jagger; cucumber, Mr. 
 W. W. Gilbert and Mr. W. N. Ankeney; potato, Dr. H. A. Edson, Prof. L. R. Jones, 
 Dr. L. O. Kunkel, Dr. W. A. Orton, Mr. M. Shapovalov, Mr. E. S. Schultz, and Dr. 
 H. G. MacMillan; onion, Dr. J. C. Walker; lettuce, spinach, radish, etc., Dr. I. C. 
 Jagger, Mr. J. B. Norton and Mr. L. P. Byars ; tomato, Mr. G. H. Godfrey, Mr. F. J. 
 Pritchard, Dr. J. Rosenbaum and Mr. W. B. Clark; watermelon, Mr. F. C. Meier; sweet 
 potato, Dr. L. L. Harter and Dr. J. L. Weimer. 
 
 922 
 
2 U. S. DEPARTMENT OF AGRICULTURE. 
 
 trol and prevention of diseases, with the resultant improve- 
 ment of American agriculture and the elimination of waste. 
 Inspectors should make it a point to send in material con- 
 cerning which they are in doubt. By doing this they will aid 
 themselves in acquiring a better acquaintance with the vari- 
 ous diseases, and will aid in the detection of new diseases or 
 of the occurrence of diseases in regions from which they 
 have not been previously reported. Cartons and franked 
 tags will be supplied the inspectors for use in sending such 
 material. Many specimens can best be sent wrapped in 
 paper (newspaper does admirably). It is very important 
 that material be mailed without delay. 
 
MARKET DISEASES OF VEGETABLES. 
 
 INTRODUCTION. 
 
 THE NORMAL PLANT. 
 Plants and Plant Parts Are Living. 
 
 T VEGETABLES and fruits are plants or plant parts and 
 V are alive. Few people realize that a potato, an onion, 
 an apple, or other fruit or vegetable is alive and is therefore 
 subject to injury, disease, and death. Failure to realize this 
 fact is responsible for much of the loss in the handling of 
 fruits and vegetables. 
 
 The Structure of Plants. 
 
 Our agricultural plants are composed of members or 
 organs, such as the root, stem, leaf, flower, and fruit. These 
 organs in turn are composed of tissues, the stem, for 
 example, usually being composed of pith, ring, and bark 
 tissue. Tissues, finally, are made up of cells, which are 
 microscopic in size. 
 
 Plant tissues often are classified according to their func- 
 tions. There are, for example, the protective tissues, the 
 supporting tissues, the conductive tissues, the food-making 
 tissues, and the storage tissues. 
 
 The Plant Cell and Tissues. 
 
 The cell is the unit of composition, structure, and function 
 of all plants. It is composed of the living substance proto- 
 plasm, together with its products and inclusions. One of 
 the products of the jelly-like protoplasm is the rigid cell 
 wall in which it encases itself and which gives shape and 
 rigidity to the cell and to the tissues. Tissues and cell walls 
 often remain intact long after the protoplasm has died. In 
 some diseases, the cementing substance which holds adjoin- 
 ing cells together is dissolved out, and disintegration of the 
 tissue results. In other cases the cell walls are punctured 
 and the protoplasm is killed. Chemical analysis of plant 
 tissues, which are, of course, composed of cells, yields prin- 
 cipally water, proteins, carbohydrates, fats, and salts. Water 
 is by far the most abundant single constituent, most plant 
 tissues containing 70-75 per cent water. 
 
 The structure of plant tissues is roughly comparable to 
 that of honeycomb except that the cells of plant tissues are 
 not as closely packed as those of honeycomb. There are 
 spaces between plant cells, called intercellular spaces, which 
 are most marked in leafy tissues. These constitute the ven- 
 tilation system of the plant, and through them the cells are 
 in communication with the air. 
 
 The epidermis or outermost protective layer of cells of 
 leaves and young stems and roots has many minute open- 
 ings or breathing pores, the stomata. Through these, water 
 
4 U. S. DEPARTMENT OF AGRICULTURE. 
 
 vapor from the moist intercellular spaces escapes into the 
 air, and carbon dioxide and oxygen exchange between the 
 cells and the air takes place. The loss of water by the living 
 plant through evaporation is known as transpiration. 
 
 When unbroken, the epidermis prevents excessive loss of 
 water from the moist tissues underneath and keeps out for- 
 eign organisms such as fungi and bacteria. In older stems 
 and roots, such as the Irish potato, the protective covering is 
 composed of cork layers, in which the breathing pores are 
 present as lenticels. 
 
 The supporting tissues, such as the veins of leaves or the 
 fibers of stems, are composed of woody or thickened cells. 
 The conducting tissues, found in the veins of leaves or the 
 ring tissues of stems or roots, translocate the water and min- 
 erals taken in by the absorptive tissues of the roots, and the 
 food made in the food-making tissues. 
 
 The green color of vegetation is due to a substance known 
 as leafgreen or chlorophyll. By virtue of chlorophyll, and 
 with the aid of sunlight, the green tissues of plants are able 
 to manufacture carbohydrates (sugars and starches) from 
 the carbon dioxide of the air and the water of the soil. 
 
 These carbohydrates are the basic substances from which 
 the other principal food of plants and animals, such as fats, 
 oils, and proteins, are manufactured by green and non-green 
 cells. 
 
 Many plants possess tissues in which they accumulate 
 excess food materials. These are the storage tissues. The 
 Irish potato and the sweet potato are to a large degree com- 
 posed of storage cells in which starch and sugar, respec- 
 tively, are stored. 
 
 Digestion and Respiration. 
 
 The stored food of the potato is in the form of starch 
 grains. In the spring when the potato sprouts, the insoluble 
 starch is changed to soluble sugar, to which is due the sweet 
 taste of potatoes at that season. In ripening plant tissues, 
 insoluble, unpalatable substances, such as starch and tan- 
 nins, become soluble, aromatic, and palatable. 
 
 Another process which goes on in all protoplasm, plant or 
 animal, is respiration. The making of food out of simple 
 materials is a constructive process, whereas respiration is 
 destructive. In its simplest form, it involves a consumption 
 of oxygen, a burning or oxidation of the substances of the 
 cell, such as sugar, starch, fat, and proteins, and a liberation 
 of carbon dioxide gas, water, and energy. Part of this 
 energy is manifested as heat. The so-called "heating" of 
 crops in transit and storage generally is due to the heat 
 evolved in respiration. 
 
 The rate of respiration is greatly influenced by tempera- 
 ture. At high temperatures, respiration proceeds at a rapid 
 rate, and the food substances are soon burned up. At low 
 temperatures, the rate of respiration is so retarded that it 
 
MARKET DISEASES OF VEGETABLES. 5 
 
 becomes practically negligible. Proper aeration is essential 
 for the continued life and respiration of vegetables. The 
 carbon dioxide liberated must be removed, and the neces- 
 sary oxygen must be supplied. If respiring cells are not 
 properly aerated, they die, a'nd spoil. 
 
 The fundamental reason for the refrigeration of fruits 
 and vegetables is based upon the fact that refrigeration 
 retards respiration and digestion ; retards not only the ripen- 
 ing processes of fruits and vegetables, but also their decay, 
 which is due to the activity of bacteria and fungi. 
 
 Relation of the Plant to Its Environment. 
 
 The continued existence of protoplasm and therefore of 
 plants themselves is dependent upon external factors which 
 constitute the environment of plants. Some of these are 
 non-living, such as moisture, heat, light, and the air ; others 
 are living, such as other plants, or animals. The environ- 
 ment of a plant may vary within certain limits without 
 injury to the plant. However, if these limits are exceeded 
 for a sufficient period of time the plant becomes abnormal 
 or diseased and eventually may die. 
 
 When plants or plant parts are shipped and stored as 
 fresh food products, they are subjected to conditions very 
 unlike those prevailing in the field, and care must be exer- 
 cised to make these such that the life of the plant or plant 
 parts is still possible. This means that the external condi- 
 tions must be controlled and kept within the narrow range 
 tolerated by the plant in question. Each crop must be 
 handled in a manner suited to its peculiar requirements. 
 This will depend upon the climatic conditions prevailing 
 during the growing season and at harvest; upon the methods 
 employed for culture and harvesting; upon the presence of 
 climatic or mechanical injuries; upon the maturity at har- 
 vesting; upon the method of packing or loading; upon the 
 type of container ; upon the length of the transportation and 
 storage periods; upon the season, and upon the climatic 
 conditions to which the crop will be subjected in transit. 
 Failure to provide proper conditions for plants or plant 
 parts in transit or storage results in the loss, annually, of 
 thousands of cars of fruits and vegetables. It may result 
 merely in an inferior product so far as appearance and 
 taste are concerned, or in partial or complete decay. 
 
 The Relation of Plant Functions to Keeping Quality. 
 
 It is well known that vegetables and fruits shrink in 
 transit and storage. Some of the shrinkage is due to read- 
 justment in the pack or load. . There is in addition to this, 
 however, a real decrease in the weight and volume of the 
 crops as can be determined by weighing and measurement. 
 
 Usually there is a very considerable shrinkage immedi- 
 ately following the harvesting of a crop, due mainly to the 
 
6 U. S. DEPARTMENT OF AGRICULTURE. 
 
 loss of water vapor by the plant through its stomata,- or 
 transpiration, and by evaporation from cut surfaces. The 
 loss of water by plant organs is illustrated very strikingly 
 by the phenomenon commonly known as "sweating," which 
 is the result of condensation of this water vapor. 
 
 The first result of excessive water loss is known as wilting. 
 Wilting is especially frequent in leafy crops with large 
 transpiring surfaces, such as celery, lettuce, or spinach. The 
 compact, heavy crops such as deciduous and citrus fruits, 
 potatoes, and onions are made up of storage tissues and are 
 much less subject to water loss than the more leafy ones. 
 They lose water much more slowly because of their rather 
 thick protective skin and fewer stomata. They also have a 
 greater bulk of water available in their tissues, and a larger 
 volume of tissue relative to their transpiring surface. 
 
 Drying of the surfaces of plants, with a slight wilting of 
 leafy plants, before they are shipped or stored is advisable. 
 Wet plant surfaces favor the development of bacteria and 
 fungi and, when stomata are filled with water, easy ingress 
 is provided for bacteria. Many crops are sweated, cured, 
 or kiln-dried before they are put into storage or shipped, 
 to avoid undue shrinkage by loss of water, and to dry and 
 harden the tissues to render them less subject to attack by 
 bacteria or fungi which flourish on tender tissues under 
 moist conditions. Continued loss of water by plant tissues 
 soon results in their death after which they may become the 
 prey of bacteria and fungi. 
 
 i Not all of the decrease in weight of fruits and vegetables 
 in storage is due to loss of water. A thoroughly cured sweet 
 potato loses weight and shrinks in storage even when stored 
 in a very humid atmosphere, especially if the temperature 
 is high. A part of this loss is due to transpiration, the 
 remainder to respiration. At low temperatures, the pro- 
 cesses go on very slowly, but ultimately lead to physiological 
 breakdown. In other words, there is a time limit to the 
 storage of all living plant parts. The period is especially 
 brief in the case of succulent crops. Each crop has its period 
 beyond which it is not advisable to store it. For example, 
 a Jonathan apple cannot be stored as long as a Winesap. 
 
 Proper aeration and refrigeration are essential in storage 
 places. The former prevents the accumulation of water 
 vapor and attendant sweating, provides oxygen, and re- 
 moves carbon dioxide. The latter decreases the rate of 
 digestion and respiration in the plant tissue, thus lowering 
 the rate at which the latter consumes itself. More impor- 
 tant, however, is the effect of these factors upon the bacteria 
 and fungi which, because of their power to cause decay, are 
 the chief enemies of stored fruits and vegetables. Bacteria 
 and fungi cannot attack plants when the plant surfaces are 
 dry. Furthermore, at low temperatures their activity is so 
 reduced that they seldom attack plant tissues. 
 
MARKET DISEASES OP VEGETABLES. 7 
 
 DISEASE IN PLANTS. 
 
 Disease in plants is any deviation from the normal con- 
 dition of their functions or tissues. The majority of plant 
 diseases as they occur in the market are localized in their 
 effects and differ therein from most animal diseases, which 
 usually are systemic, and affect the whole body because 
 of the presence of a nervous and a circulatory system. For 
 example, the outer leaves of a celery plant may be rotted 
 severely while the inner leaves or heart are in no way 
 injured and are fit for food. It must be remembered, how- 
 ever, that the sound part of a fruit and vegetable may in 
 some cases acquire a disagreeable odor or flavor from the 
 diseased part. At times even sound fruits or vegetables are 
 affected in taste and flavor by nearby decaying fruits and 
 vegetables. 
 
 Types. 
 
 Diseases may occur in the growing plant, checking and 
 preventing its growth or its production of normal parts or 
 even killing it outright. They may also occur in fruits and 
 vegetables in transit and storage. We may therefore distin- 
 guish between field and transportational diseases, and shall 
 attempt to differentiate as much as possible between dis- 
 eases which originate in the field and those which originate 
 in transit and storage. 
 
 For example, infection of sweet potatoes with soft rot or 
 peaches with brown rot may occur either in the field, in 
 transit, or in storage, whereas infection of sweet potatoes 
 with scurf or peaches with scab occurs only in the field. 
 The first two diseases, however, may develop or progress in 
 the field, in transit, or in storage, whereas the latter two 
 probably do not develop or spread in transit or in storage. 
 
 Symptoms. 
 
 The signs or characteristics of a disease which mark it 
 and by which its presence is discerned, are known as the 
 symptoms of the disease. During the progress of a disease, 
 its symptoms may change. Frequently there are early and 
 advanced symptoms. The early symptoms of watermelon 
 anthracnose, for example, are raised welts on the rind, 
 while the advanced symptoms are deeply sunken lesions 
 with a salmon pink covering of spores. 
 
 Not all the symptoms of a disease necessary for its diag- 
 nosis may appear on one specimen. As a matter of fact, 
 it is often impossible to diagnose a disease by examining a 
 single specimen, and a correct diagnosis often involves an 
 examination of the whole field or the entire lot in the car 
 or in storage. In a shipment of celery, for example, some 
 plants may show a watery rot. This condition alone may be 
 insufficient for a correct and complete diagnosis. Other 
 plants in the same shipment may show a white cottony 
 
8 U. S. DEPARTMENT OF AGRICULTURE. 
 
 growth of mold and no rot, while others may show the mold 
 and black masses of the fungus. The presence of all of 
 these symptoms in a package or car, however, furnish the 
 basis for a correct diagnosis of the rot as watery soft rot due 
 to Sclerotinia. 
 
 Very frequently the symptoms of several diseases appear 
 on the same specimen or in the same lot. A single potato 
 may show symptoms of black scurf, black heart, and Fusa- 
 rium tuber rot at the same time. Sometimes the symptoms 
 of one disease are followed immediately by those of another, 
 as in black heart of potatoes followed by slimy soft rot. 
 
 Diseases Due to Living, Parasitic Agencies. 
 
 Most plant diseases are caused by one of two types of 
 minute plant life, commonly known as germs and molds and 
 often referred to collectively as "microorganisms." 
 
 Host and Parasite. 
 
 The plant attacked and at whose expense the bacteria 
 or fungi feed, and upon and in which they live, is known as 
 the host. Bacteria or fungi living upon and at the expense 
 of a living plant or animal are known as parasites. When 
 these live upon dead plant or animal matter they are classed 
 as saprophytes. Some bacteria and fungi are restricted to 
 a single host; others can attack a variety of hosts. Diseases 
 due to the latter type of organisms are more likely to origi- 
 nate in transit and storage than those due to the former 
 type. 
 
 Bacteria and Fungi. 
 
 Bacteria are exceedingly small, single-celled, non-green 
 plants which multiply by simple division. Under proper 
 conditions of temperature, moisture, and food supply, bac- 
 teria multiply with astounding rapidity. 
 
 Some fungi also are composed of single cells, but most of 
 them consist of many cells united end to end to form threads. 
 A single thread is known as a hypha (plural hyphae) and 
 the mass of hyphae of a fungus is known as the mycelium. 
 Generally the mycelium grows within the tissues of the 
 host and is invisible, although under favorable conditions it 
 may also grow out on the surface. At times the mycelium 
 of some fungi form thickened, hardened masses known as 
 sclerotia. 
 
 Fungi generally reproduce by the formation and libera- 
 tion of special cells or groups of cells called spores. In 
 function, these spores are the equivalent of the seed of 
 higher plants, and are distributed as these are, by man, 
 animals, wind, and water. They are, of course, distributed 
 very much more readily and widely because they are so 
 small and light. The spores of some fungi, such as "blue 
 mold" or "bread mold" are found everywhere. 
 
MARKET DISEASES OF VEGETABLES. 9 
 
 Fungi bear their spores in various ways. In the simpler 
 types the spores are borne on the surface of the attacked 
 plant as a powdery or dusty covering such as one sees in 
 blue mold (Penicillium) and gray mold (Botrytis). Some, 
 such as Rhizopus nigricans, bear their spores in special cases 
 called sporangia, (singular, sporangium). The summer 
 spores of many fungi are known as conidia (singular, 
 conidium). 
 
 In other fungi, spores are produced in slimy heaps on 
 little pads or cushionlike bodies known as acervuli (singu- 
 lar, acervulus) . These are especially marked in the anthrac- 
 noses. Still other fungi bear their spores in special flask- 
 shaped bodies on or at the surface of the diseased portion 
 of the attacked plant. These appear as dots, or pimple-like 
 bodies and are known as pycnidia (singular, pycnidium). 
 They are conspicuous in the late blight spots on celery, the 
 fruit rot of egg plant, the Phoma rot of tomatoes, and the 
 black rot of apples. The special spore-bearing structures 
 of fungi are known as fruiting bodies. The fruiting bodies 
 which result from fertilization and contain the winter spores 
 do not occur generally under market and storage conditions. 
 
 There are four classes of fungi, Phycomycetes, Ascomy- 
 cetes, Fungi Imperfecti, and Basidiomycetes. Most of the 
 fungi with which we will deal belong to the third of these 
 groups. 
 
 The Life Processes of Bacteria and Fungi. 
 
 The protoplasm of bacteria and fungi lacks chlorophyll 
 and therefore cannot manufacture its own food, but must 
 obtain it from green plants, either directly or indirectly. It 
 obtains its food and energy by digestive and respiratory 
 processes from the tissue attacked. This digestive and 
 respiratory action of bacteria and fungi is popularly known 
 as fermentation. Bacterial rots generally are accompanied 
 by putrefactive odors due to the breaking down of protein 
 compounds. 
 
 The attack upon living tissues by parasites leads to a dis- 
 turbance in the functions, structure, and composition of the 
 attacked plant, in other words, to disease. The diseased 
 areas produced by parasites or other causes are known as 
 lesions. At present only those produced by the action of 
 parasites will be considered. A lesion may be a leaf or 
 pod-spot, a wart, a soft or dry-rot, or a canker, depending 
 upon the parasite, the external conditions, and the nature 
 and response of the affected host tissues. Soft rot of the 
 carrot, for example, consists of lesions caused by Bacillus 
 carotovorus. These bacteria secrete ferments or enzymes 
 which digest or dissolve the cementing substances between 
 the carrot cells and disintegrate the tissue into a soft, slimy 
 mass. 
 
 In other diseases the lesions arise in a different manner. 
 In anthracnose of the cucumber, for example, the hyphae 
 
10 U. S. DEPARTMENT OF AGRICULTURE. 
 
 of the fungus, Colletotrichum lagenarium, penetrate the cell 
 walls and feed upon the protoplasm. As a result, the 
 affected cells die and lose their water, consequently one of 
 the first symptoms of the disease is a water-soaked spot on 
 the fruit. Since the water evaporates rapidly from this spot, 
 it dries out and becomes sunken. As more cells are killed 
 and the lesion enlarges, cavities result from the shrinkage 
 and rupture of the killed tissue. In other diseases, such as 
 late blight of the potato, the fungus grows between the cells 
 and sends suckers into the cells, thereby securing its nour- 
 ishment, and eventually killing the host protoplasm. 
 
 The activity of the bacteria and fungi, like that of other 
 plants, is greatly influenced by temperature. Low tempera- 
 tures inhibit the germination and growth of these parasites, 
 consequently are useful in controlling many diseases. Low 
 temperatures also retard digestion and respiration in these 
 organisms, consequently decrease their destructive activities. 
 These facts are fundamental reasons for the refrigeration 
 of fruits and vegetables. Control of the life processes of 
 these organisms by low temperatures probably is more 
 important than the effect of refrigeration upon the life 
 activities of the stored fruits or vegetables. Some fungi and 
 bacteria can grow well at moderate temperatures and conse- 
 quently are very active even in iced cars. Scletotinia, for 
 example, grows well at moderate temperatures and there- 
 fore causes a rot of celery in iced cars. 
 
 Active bacterial and fungous cells do not possess the effec- 
 tive protective tissues of higher plants, consequently their 
 protoplasm is very subject to drying out. In the desiccated 
 state these organisms are inactive or resting, and cannot 
 resume growth or develop so long as they are dry. In com- 
 bating diseases caused by parasites, it is fundamentally 
 important to recognize the fact that a moist environment is 
 essential for their growth and spread. Dried or slightly 
 wilted plant tissues, when shipped or stored in a well aer- 
 ated place, are not attacked readily by bacteria and fungi. 
 Loading or storing wet fruits or vegetables often leads to 
 disastrous results because of the action of micro-organisms. 
 
 Inception of Diseases Due to Bacteria and Fungi. 
 
 While bacterial cells and fungous spores are everywhere 
 present in great numbers on the exposed surfaces of all 
 normal uninjured plant parts, the interior tissue is usually 
 absolutely sterile ; that is, free from all foreign organisms. 
 
 Before disease can occur infection must take place. By 
 infection we mean the entrance of the disease-producing 
 organism into the host tissue and its development therein. 
 Plants are protected against the entrance of foreign organ- 
 isms by their epidermis, by their cork layers, and by the 
 nature of their protoplasm. Foreign organisms may gain 
 entrance through the unbroken skin, or through natural 
 openings in the epidermis such as stomata and water pores. 
 
MARKET DISEASES OF VEGETABLES. 11 
 
 However they generally enter plant tissues through wounds 
 or abrasions of the protective layers. This type of infection 
 is the most important in transportational diseases. Injured 
 or dead areas offer an 'excellent foothold for rot-producing 
 organisms. 
 
 Diseases Due to Non-living, Non-parasitic Causes. 
 
 A very considerable number of plant diseases are due not 
 to parasitic organisms but to other unfavorable factors in 
 the environment of the plants. Water core and Jonathan 
 spot of apples, black heart, hollow heart, and sunburn of 
 potatoes, tip-burn of lettuce and other crops, and scald and 
 freezing or chilling injury of vegetables and fruits are excel- 
 lent examples of disease due to non-parasitic causes. 
 
 Tip-burn of lettuce and other plants, water core and 
 Jonathan spot of apples, and blossom-end rot of tomatoes 
 and watermelons probably are due to irregularities in the 
 water relations of these crops. The nature of the plants 
 themselves is also a very important factor in such troubles. 
 For example, with the same soil and climatic conditions, the 
 same water supply, and the same treatment of trees of vari- 
 ous varieties, the Jonathan and the 'Grimes Golden alone 
 may show Jonathan spot. Black heart of potatoes is a good 
 example of the evil effects of disturbed respiration in plants. 
 
 Under normal conditions, oxygen enters the internal 
 tissues of the potato at a rate sufficiently rapid to maintain 
 normal respiration. However, if the temperature is raised 
 to 100 F., the rate of respiration is so increased that oxygen 
 cannot penetrate to the inner cells rapidly enough to supply 
 their needs. As a result the internal tissues of the tuber 
 become asphyxiated, die, and turn black. 
 
 If potatoes are kept at normal temperatures but are not 
 well aerated and do not have a normal supply of oxygen, 
 black heart also results. In this case the death and dis- 
 coloration of the cells is not restricted to the heart of the 
 potato. 
 
 Chilling and freezing injury are good examples of the 
 effects of excessively low temperature upon plant tissues, 
 while sunscald is an example of the effect of extremely high 
 temperature. Either extreme kills the tissues. 
 
 Tolerance, Resistance and Predisposition to Disease. 
 
 Many plants have to a certain degree an ability to tolerate 
 unfavorable climatic, soil, and cultural conditions, and to 
 withstand or tolerate the attacks of bacteria and fungi. 
 This tolerance varies with the age and variety of the plant 
 and with the conditions under which the plant is grown. 
 
 Resistance to parasitic attack may be due to the nature 
 and thickness of the protective covering of the plant, to a 
 scarcity of natural openings, to the rapidity with which 
 wounds heal over (with wound cork), to the time of ma- 
 
12 . U. S. DEPARTMENT OF AGRICULTURE. 
 
 turity of the plant, to the acidity of its tissues, or more 
 commonly to some unknown factor in the composition of the 
 protoplasm of the cells themselves. * 
 
 Disease Control. 
 
 By disease control is meant the elimination, the checking, 
 or the prevention of a disease. Plant diseases usually are 
 controlled by prevention rather than cure. A very gener- 
 ally used method in the control of diseases due to parasites 
 is the spraying, dusting, or dipping of plants or plant parts 
 to kill the fungi and bacteria present on the surfaces, or to 
 prevent the germination of spores that may lodge thereon 
 subsequently. There are a number of other practical 
 methods of disease control, such as proper cultural methods, 
 crop rotation, soil and seed sanitation, planting of disease- 
 free stock or disease-resistant varieties, and the variation 
 of the planting date. 
 
 In the control of transportational diseases, icing, refrig- 
 eration, ventilation, precaution not to pack wet plants or 
 plant organs, drying of plants, and careful handling are 
 important means of disease control. 
 
MARKET DISEASES OF VEGETABLES. 13 
 
 LITERATURE CITED. 
 
 In addition to these special references, the following books will be 
 found very helpful and should be freely consulted : 
 
 Freeman, E. M. Minnesota plant diseases. 1905. 
 
 Duggar, B. M. Fungous diseases of plants. 1909. 
 
 Stevens, F. L., and Hall, J. G. Diseases of economic plants. 1910. 
 
 Hesler, L. R., and Whetzel, H. H. Manual of fruit diseases. 1917. 
 
 Coons, G. H., and Nelson, R. The plant diseases of importance in the 
 transportation of fruits and vegetables. Am. Ry. Perishable Freight 
 Assn. Cir. 473-A. 1918. 
 
 (1) Bartholomew, E. T. 
 
 1913. Black heart of potatoes. In Phytopathology, v. 3, No. 3, 
 
 p. 180-182, pi. 19. 
 
 (la)Bessey, E. A., and Byars, L. P. 
 
 1915. The control of root-knot. U. S. Dept. Agr. Farmers' Bui. 
 648, 19 p. 
 
 (2) Brandes, E. W. 
 
 1918. Anthracnose of lettuce caused by Marssonina panattoni- 
 ana. In Jour. Agr. Research, v. 13, No. 5, p. 261-280, 
 4 fig., pi. C, 20. Literature cited, p. 280. 
 
 (3) Brooks, Charles. 
 
 1914. Blossom-end rot of tomatoes. In Phytopathology, v. 4, 
 
 No. 5, p. 345-374, 4 fig., pi. 24-26. References, p. 
 372-373. 
 
 (4) Brown, Nellie A. 
 
 1915. A bacterial disease of lettuce.* A preliminary report. 
 
 In Jour. Agr. Research, v. 4, No. 5, p. 475-478. Litera- 
 ture cited, p. 478. 
 
 (5) Burger, O. F. 
 
 1913. Lettuce drop. Fla. Agr. Exp. Sta. Bui. 116, p. 27-32, 
 
 illus. 
 
 (6) 
 
 1914. Cucumber rot. Fla. Agr. Exp. Sta. Bui. 121, p. 97-109, 
 
 fig. 37-42. 
 
 (7) Carpenter, C. W. 
 
 1915. Some potato tuber-rots caused by species of Fusarium. 
 
 Jour. Agr. Research, v. 5, No. 5, p. 183-210, pi. A-B, 
 14-19. 
 
 (8) Carsner, Eubanks. 
 
 1918. Angular-leafspot of cucumber: dissemination, overwin- 
 tering and control. In Jour. Agr. Research, v. 15, No. 
 3, p. 201-220, pi. 13-16. Literature cited, p. 220. 
 
 (9) Chittenden, F. H., and Orton, W. A. 
 
 1918. How to increase the potato crop by spraying. U. S. Dept. 
 Agr. Farmers' Bui. 868, p. 13-16. 
 
 (10) Cook, M. T., and Lint, H. C. 
 
 1915. Potato diseases in New Jersey. N. J. Agr. Exp. Sta. Circ. 
 
 53, 23 p., 9 fig. Substitute for Circ. 33, now out of 
 print. 
 
 (11) Coons, G. H.. and Levin, Ezra. 
 
 1916. The Septoria leaf spot disease of celery, or celery blight. 
 
 Mich. Agr. Exp. Sta. Spec. Bui. 77, 8 p., 9 fig. 
 
 * Papers marked with a star are exhausted so far as the Department supply is 
 concerned. Copies may be purchased from the Superintendent of Documents, Govern- 
 ment Printing Office, Washington, D. C. 
 
14 U. S. DEPARTMENT OF AGRICULTURE. 
 
 (12) Doolittle, S. P. 
 
 1916. Cucumber scab caused by Cladosporium cucumerinum. 
 In 17th Rpt. Mich. Agr. Acad. Sci. [1915]: 87-116. 
 Literature, p. 116. 
 
 (13) 
 
 1916. A new infectious mosiac disease of cucumber. In Phyto- 
 pathology, v. 6, No. 2, p. 145-147. 
 
 (14) Edgerton, C. W. 
 
 1910. The bean anthracnose. La. Agr. Exp. Sta. Bui. 119, 55 
 p., 14 pi. Bibliography, p. 51-54. 
 
 (15) and Moreland, C. C. 
 
 1913. The bean blight and preservation and treatment of bean 
 
 seed. La. Agr. Exp. Sta. Bui. 139, 43 p., 6 pi. 
 
 (16) Edson, H. A. 
 
 1915. Rheosporangium aphanidermatum, a new genus and 
 species of fungus parasitic on sugar beets and radishes. 
 In Jour. Agr. Research, v. 4, No. 4, p. 279-292, pi. 
 44-48. 
 (17) 
 
 1915. Seedling diseases of sugar beets and their relation to 
 
 root-rot and crown-rot. In Jour. Agr. Research, v. 4, 
 No. 2, p. 135-168, pi. 16-26. Literature cited, p. 
 165-168. 
 
 (18) Erwin, A. T. 
 
 1916. Late potato blight in Iowa. Iowa Agr. Exp. Sta. Bui. 
 
 163, p. 287-305, 8 fig. 
 
 (19) Galloway, B. T. 
 
 1895. The growth of lettuce as affected by the physical proper- 
 ties of the soil. In Agr. Sci., v. 8, p. 302-316. 
 
 (20) 
 
 1895. Commercial lettuce forcing. In Amer. Gard., v. 16, p. 135. 
 
 (21) Gardner, M. W. 
 
 1918. Anthracnose of cucurbits. U. S. Dept. Agr. Bui. 727, 
 68 p. 
 
 (22) Gilbert, W. W. 
 
 1916. Cucumber mosaic disease. In Phytopathology, v. 6, No. 
 2, p. 143-144, pi. 5. 
 
 (23) Harter, L. L. 
 
 1914. Fruit-rot, leaf -spot, and stem-blight of the eggplant 
 
 caused by" Phomopsis vexans. In Jour. Agr. Research, 
 v. 2, No. 55, p. 331-338, 1 fig., pi. 26-30. 
 
 (24) 
 
 1916. Sweet potato diseases. U. S. Dept. Agr. Farmers' Bui. 
 
 714, 26 p., 21 fig. 
 
 (25) 
 
 1917. Podblight of the lima bean caused by Diaporthe phaseo- 
 
 lorum. In Jour. Agr. Research, v. 11, No. 10, p. 474- 
 504, 11 fig., pi. 42-43. Literature cited, p. 502-504. 
 
 (26) and Jones, L. R. 
 
 1918. Cabbage diseases. U. S. Dept. Agr. Farmers' Bui. 925, 
 
 30 p., 13 fig. 
 
 (27) , Weimer, J. L., and Adams, J. M. R. 
 
 1918. Sweet potato storage rots. In Jour. Agr. Research, v. 
 15, No. 6, p. 337-368. 
 
 (28) Hawkins, L. A. 
 
 1916. The disease of potatoes known as "leak."* In Jour. Agr. 
 
 Research, v. 6, No. 17, p. 627-640, 1 fig., pi. 90. 
 
 (29) 
 
 1917. Experiments in the control of potato leak. U. S. Dept. 
 
 Agr. Bui. 577, 5 p. 
 
MARKET DISEASES OF VEGETABLES., 15 
 
 (30) Humbert, J. G. 
 
 1918. Tomato diseases in Ohio. Ohio Agr. Exp. Sta. Bui 321 
 p. 157-196, illus. 
 
 (31) Jagger, I. C. 
 
 1916. Experiments with the cucumber mosaic disease. In Phy- 
 
 topathology, v. 6, No. 2, p. 148-151. 
 
 (32) Jamieson, Clara O. 
 
 1915. Phoma destructiva, the cause of a fruit rot of the 
 tomato.* In Jour. Agr. Research, v. 4, No. 1, p. 1-20, 
 pi. 1-6 (2 col.). Literature cited, p. 19-20. 
 
 (33) Jones, L. R. 
 
 1901. A soft rot of carrot and other vegetables. In Vt. Agr. 
 Exp. Sta. 13th Ann. Rpt. 1899-1900, p. 299-332, illus. 
 (33a) Jones, L. R., and Bailey, Ernest. 
 
 1917. P'rost necrosis of potato tubers. In Phytopathology, v. 7, 
 
 No. 1, p. 71-72. 
 
 (34) . _, Giddings, N. J., and Lutman, B. F. 
 
 1912. Investigations of the potato fungus Phytophthora in- 
 festans.f U. S. Dept. Agr. Bur. Plant Indus. Bui. 245, 
 100 p., illus., 10 pi. (2 col.), map. 
 
 (35) Kunkel, L. O. 
 
 1919. Wart of potatoes; a disease new to the United States. 
 U. S. Dept. Agr. Bur. Plant Indus. Office Cotton, 
 Truck, and Forage Crop Diseases, Circ. 6. 
 
 (36) Levin, Ezra. 
 
 1917. Control of lettuce rot. In Phytopathology, v. 7, No. 5, p. 
 
 392-393. 
 
 (37) Link, G. K. K. 
 
 1916. A physiological study of two strains of Fusarium in their 
 causal relation to tuber rot and wilt of potato. Nebr. 
 Agr. Exp. Sta. Research Bui. 9, 45 p., illus. 
 
 (38) Lutman, B. F. 
 
 1913. The pathological anatomy of potata scab. In Phytopath- 
 
 ology, v. 3, No. 5, p. 255-264, illus. Bibliography, 
 p. 264. 
 
 (39) and Cunningham, G. C. 
 
 1914. Potato scab. Vt. Agr. Exp. Sta. Bui. 184, 64 p., 6 fig., 
 
 12 pi. Bibliography, p. 62-64. 
 
 (40) McKay, M. B., and Pool, Venus W. 
 
 1918. Field studies of Cercospora beticola. In Phytopath- 
 
 ology, v. 8, No. 3, p. 119-136, illus. 
 
 (41) MacMillan, H. G. 
 
 191 8. Sun-scald of beans. In Jour. Agr. Research, v. 13, No. 
 12, p. 647-650, pi. 64-66. 
 
 (42) Meier, F. C. 
 
 1916. Watermelon stem-end rot. [Preliminary report.] In 
 Jour. Agr, Research, v. 6, No. 4, p. 149-152, pi. 17. 
 
 (43) Melhus, I. E. 
 
 1913. Silver scurf, a disease of the potato. f In U. S. Dept. 
 
 Agr. Bur. Plant Indus. Circ. 127, p. 15-24,4 fig. Biblio- 
 graphy, p. 24. 
 
 (44) 
 
 1914. Powdery scab ('Spongospora subterranea) of potatoes.f 
 
 U. S. Dept. Agr. Bui. 82, 16 p., 3 pi. Bibliography, 
 p. 15-16. 
 
 (45) - 
 
 1915. Hibernation of Phytophthora infestans in the Irish 
 
 potato.* In Jour. Agr. Research, v. 5, No. 2, p. 7.1-102, 
 3 fig., pi. 4-8. Literature cited, p. 100-102. 
 
 t Papers marked with a dagger are out of print. 
 
16 U. S. DEPARTMENT OF AGRICULTURE. 
 
 (46) Morse, W. J. 
 
 1914. Powdery scab of potatoes. Maine Agr. Exp. Sta. Bui. 
 227, p. 87-104, fig. 44-52. 
 
 (47) Muncie, J. H. 
 
 1914. Two Michigan bean diseases. Mich. Agr. Exp. Sta. Spec. 
 
 Bui. 68, 12 p., 2 fig., 1 pi. (col.). 
 
 (48) Munn, M. T. 
 
 1917. Neck-rot disease of onions. N. Y. State Agr. Exp. Sta. 
 Bui. 437, p. 361-455, 11 pi. Bibliography, p. 450-455. 
 
 (49) Orton, C. R. 
 
 1916. The diseases of the potato. Penn. Agr. Exp. Sta Bui. 
 
 140, 37 p., 23 fig. 
 
 (50) Orton, W. A. 
 
 1913. Potato tuber diseases.' U. S. Dept. Agr. Farmers' Bui. 
 544, 16 p., illus. 
 
 (51) 
 
 1917. Watermelon diseases. U. S. Dept. Agr. Farmers' Bui. 
 
 821, 18 p., 11 fig. 
 
 (52) Osmun, A. V., and Anderson, P. T. 
 
 1915. Ring-spot of cauliflower. In Phytopathology, v. 5, No. 5, 
 
 p. 260-265, 4 fig. Literature cited, p. 265. 
 
 (53) Pratt, O. A. 
 
 1916. Control of the powdery dryrot of western potatoes 
 
 caused by Fusarium trichothecioides.* In Jour. Agr. 
 Research, v. 6, No. 21, p. 817-831, pi. 108. 
 
 (54) 
 
 1916. A western field-rot of the Irish potato tuber caused by 
 Fusarium radicicola. In Jour. Agr. Research, v. 6, 
 No. 9, p. 297-310, pi. 34-37. 
 
 (55) Rogers, S. S. 
 
 1911. The late blight of celery. Calif. Agr. Exp. Sta. Bui. 208, 
 
 p. 83-115, illus., 1 pi. 
 
 (56) Rosenbaum, Joseph 
 
 1918. The origin and spread of tomato fruit rots in transit. 
 
 In Phytopathology, v. 8, No. 11, p. 572-580, illus., 
 pi. 4. 
 
 (57) Schultz, E. S. 
 
 1916. Silver-scurf of the Irish potato caused by Spondylocla- 
 
 dium atrovirens.* In Jour. Agr. Research, v. 6, No. 
 10, p. 339-350, pi. 45-48. Literature cited, p. 350. 
 
 (58) Sheldon, J. L. 
 
 1904. Diseases of melons and cucumbers during 1903 and 1904. 
 W. Va. Agr. Exp. Sta. Bui. 94, p. 119-138, pi. 1-5. 
 
 (59) Sherbakoff, C. D. 
 
 1917. Buckeye rot of tomato fruit. In Phytopathology, v. 7, 
 
 No. 2, p. 119-129, 5 fig. 
 
 (60) 
 
 1917. Some important diseases of truck crops in Florida. Fla. 
 Agr. Exp. Sta. Bui. 139, p. 191-277, fig. 76-112. 
 
 (61) Smith, Erwin F. 
 
 1911-14. Bacteria in Relation to Plant Diseases, v. 2, 1911; 
 v. 3, 1914. Washington, D. C. (Carnegie Inst. Wash- 
 ington Pub. 27, v. 2-3. ) 
 
 (62) , and Bryan, Mary K. 
 
 1915. Angular leaf -spot of cucumbers.* In Jour. Agr. Re- 
 search, v. 5, No. 11, p. 465-476, pi. 43-49. 
 
 (63) Spaulding, Perley, and Field, Ethel C. 
 
 1912. Two dangerous imported plant diseases. f U. S. Dept. 
 
 Agr. Farmers' Bui. 489, 29 p., 3 fig. 
 
 (64) Stakman, E. C., and Tolaas, A. G. 
 
 1912. Potato diseases. Minn. Agr. Exp. Sta. Ext. Bui. 35, 15 
 p., 7 fig. 
 
MARKET DISEASES OF VEGETABLES. 17 
 
 (65) Stevens, F. L. 
 
 1911. A serious lettuce disease (lettuce sclerotiniose). N. C. 
 Agr. Exp. Sta. Bui. 217, p. 7-21, illus. 
 
 (66) , and Hall, J. G. 
 
 1911. A serious lettuce disease (sclerotiniose) and a method 
 of control. N. C. Agr. Exp. Sta. Tech. Bui. 8, p. 89- 
 143. Bibliography, p. 144. 
 
 (67) Stewart, F. C. 
 
 1899. Notes on various plant diseases. I. A bacterial rot of 
 onions. In N. Y. State Agr. Exp. Sta. Bui. 164, p. 
 209-212, pi. 1-2. 
 
 (68) , and Mix, A. J. 
 
 1917. Blackheart and the aeration of potatoes in storage. 
 
 N. Y. Agr. Exp. Sta. Bui. 436, p. 319-362, 10 pi. 
 
 (69) Taubenhaus, J. J. 
 
 1918. Pox, or pit (soil rot), of the sweet potato. In Jour. Agr. 
 
 Research, v. 13, No. 9, p. 437-450, pi. 51-52. Litera- 
 ture cited, p. 449-450. 
 
 (70) - , and Manns, T. F. 
 
 1915. The diseases of the sweet potato and their control. Del. 
 
 Agr. Exp. Sta. Bui. 109, 55 p., 65 fig. Literature on 
 potato diseases, p. 48-51. 
 
 (71) Thaxter, Roland. 
 
 1890. The "smut" of onions. Conn. Agr. Exp. Sta. Ann. Rpt. 
 1889, p. 129-154, pi. 1-3. 
 
 (72) 
 
 1890. The onion Vermicularia (Vermicularia circinans). Conn. 
 
 Agr. Exp. Sta. Ann; Rpt. 1889, p. 163-165. 
 (72a)Tisdale, W. H. 
 
 1916. A Melanconium parasitic on the tomato. In Phytopath- 
 
 ology, v. 6, p. 390-394. 
 
 (73) Van Hook, J. M. 
 
 1906. Blighting of field and garden peas, chiefly due to seed 
 infection. Ohio Agr. Exp. Sta. Bui. 173, p. 229-249, 
 12 fig. 
 
 (74) Van Pelt, Wayne. 
 
 1917. Black mold of onions. Ohio Agr. Exp. Sta. Mo. Bui., v. 
 
 2, No. 5, p. 152-156, illus. 
 
 (75) Whetzel, H. H. 
 
 >906. Some diseases of beans. N. Y. Cornell Agr. Exp. Sta. 
 Bui. 239, p. 195-214, illus. 
 
 (76) 
 
 1908. Bean anthracnose. N. Y. Cornell Agr. Exp. Sta. Bui. 
 255, p. 429-447, fig. 217-222. 
 
18 U. S. DEPARTMENT OF AGRICULTURE. 
 
 GRAY MOLD ROT 
 
 OF ARTICHOKE, BEET, CABBAGE, CARROT, CAULIFLOWER, CITRON, LET- 
 TUCE, ONION, PARSNIP, RHUBARB, RUTABAGA, SALSIFY, SHALLOTS, 
 TURNIP, AND OTHER VEGETABLES. 
 
 Cause : A fungus (Botrytis) . 
 
 This is a semi-watery to watery soft rot characterized 
 externally by a gray velvety fungous growth. Frequently 
 there is a slight tinge of green or brown in the gray color of 
 this mold. At times gray to black solid masses known as 
 sclerotia are produced on the affected tissues as in the case 
 of the gray mold rot of onions generally known as "neck 
 rot." 
 
 Gray mold rot can be differentiated from the watery soft 
 rot caused by Sclerotinia by the gray color of the mold and 
 by the absence of a cottony mycelium. 
 
 Gray mold rot can be differentiated from slimy soft rot 
 by the gray fungous growth and by the absence of offensive 
 odors. Rhizopus rot can be differentiated from gray mold 
 rot by its abundant stringy and coarse mycelium, its spo- 
 rangia, and its sour odor. 
 
 In case of doubt as to the identity of a given rot, it is 
 advisable to collect and incubate some material in a warm 
 damp-chamber secured either by wrapping it in paper or 
 by placing it in covered pans. If a mycelium develops 
 within 24 hours, the rot is not slimy soft rot. If a white 
 cottony mycelium develops which later becomes matted, the 
 fungus is probably Sclerotinia. A grayish, powdery fungous 
 growth indicates Botrytis, and a stringy mycelium with 
 sporangia, Rhizopus. The presence of sclerotia will further 
 indicate either Sclerotinia or Botrytis. 
 
 Often the watery soft rot due to Sclerotinia and the gray 
 mold rot due to Botrytis occur either together or^in close 
 succession on the same specimen. 
 
 Gray mold rot does not progress as rapidly as watery 
 soft rot and, like slimy soft rot, may be checked by drying 
 affected tissues, while watery soft rot (due to Sclerotinia) 
 progresses rapidly even under dry atmospheric conditions. 
 
 Infection takes place in the field, in transit, and in storage 
 since the spores of the fungus seem to be everywhere pres- 
 ent. The fungus may develop in the field if moist weather 
 prevails. 
 
 The rot occurs commonly in mature tissues kept in a very 
 humid atmosphere. It attacks frozen or bruised tissues very 
 readily. 
 
 Affected stock may be made marketable if trimmed and 
 kept in a dry, well-ventilated place. It is not safe to store 
 affected stock because it is a menace to healthy stock, the 
 fungus spreading readily from affected to healthy tissues. 
 
 Little is known about the control of this rot, but soil 
 aeration and proper ventilation in transit and storage are 
 preventive measures. The neck rot type of this rot found 
 
MARKET DISEASES OF VEGETABLES. 19 
 
 on onion bulbs can be checked by rapid curing of the onions 
 as soon as they are dug. 
 Ref. (48).* 
 
 RHIZOPUS ROT. 
 
 OF BEAN, BEET, CABBAGE, CARROT, ONION, SQUASH, SWEET POTATO, 
 TOMATO, AND OTHER VEGETABLES. 
 
 Cause: A fungus (Rhizopus). 
 
 In its early stages, Rhizopus rot consists of soft, water- 
 soaked areas. These enlarge rapidly and often lead to a 
 leaky condition of affected stock. Under proper moisture 
 conditions, there is produced a coarse, white, stringy mycel- 
 ium bearing white, glistening heads or sporangia, which 
 later turn brown or black. This mycelium is often called 
 "whiskers" because of the long, loose growth of hyphae. 
 
 Generally the rot is accompanied by a sour, acid odor, 
 noticeable when the diseased tissue is freshly broken. In 
 carrots, sweet potatoes, and other crops which are rich in 
 starches and sugars, acetic acid is produced, giving rise to 
 a vinegar-like odor. In cabbage lactic acid is produced and 
 an odor of sauer kraut is the result. 
 
 This rot is distinguishable from watery soft rot by its sour 
 odor and by the presence of the fluffy, stringy mycelium 
 with its sporangia. The mycelium of Sclerotinia is white 
 and cottony or matted. In advanced stages, the Rhizopus 
 mycelium collapses, becomes matted, and appears gray or 
 brown, but lacks the black sclerotia of Sclerotinia. 
 
 The sporangia, the color of the mycelium, and the sour 
 odor of the rot distinguish it from gray mold rot, and the 
 presence of the mycelium distinguishes it from slimy soft rot. 
 
 Rhizopus rot is favored by high temperatures. In this 
 respect it differs from watery soft rot or gray mold rot, 
 both of which develop best at moderate temperatures. It 
 is common in overheated, humid cars, especially in the sum- 
 mer, or in refrigerated cars in which the ice was allowed 
 to run low. 
 
 Usually the fungus gains entry through wounds. The 
 original infections may take place in the field, in transit, or 
 in storage since the spores of the fungus seem to be every- 
 where present. The rot develops and spreads very rapidly. 
 Like Sclerotinia, Rhizopus spreads from affected to healthy 
 stock by contact. 
 
 Sorting out of bruised stock, drying of moist surfaces, 
 and proper ventilation and refrigeration will act as effec- 
 tive control measures in transit and storage. 
 
 SLIMY SOFT ROT. 
 
 OF BEAN, BEET, CABBAGE, CARROT, CELERY, LETTUCE, MUSTARD, ONION, 
 POTATO, RADISH, RUTABAGA, SHALLOTS, SPINACH, TURNIP, AND OTHER 
 VEGETABLES. 
 
 Cause: Bacteria (Bacillus carotovorus group and other 
 bacteria). 
 
 *Reference is made by number to "Literature cited," pp. 13-17. 
 
20 U. S. DEPARTMENT OF AGRICULTURE. 
 
 This disease is a soft rot characterized by a slimy, slippery 
 condition of the affected tissues, by a foul odor, and by the 
 absence of fungous growth. The last characteristic differ- 
 entiates it from rots caused by fungi. Green, leafy tissues 
 affected with slimy soft rot have a very dark green color at 
 first much like hashed spinach but later become brown and 
 black. Light colored tissues, such as cabbage and celery, 
 become yellowish and finally brown. 
 
 Slimy soft rot is differentiated from gray mold rot by the 
 absence of the powdery, gray growth of mold and of the 
 gray to black sclerotia characteristic of gray mold rot. The 
 offensive odor of slimy soft rot distinguishes it from the rot 
 due to Rhizopus, which has an acid odor. Tissues affected 
 with slimy soft rot do not leak as do tissues affected with 
 watery soft rot, but become a mass of slime if kept in a 
 moist place. Watery soft rot progresses even in a dry 
 atmosphere after once well started, whije the progress of 
 slimy soft rot is arrested by drying of the tissues. 
 
 The rot proceeds from any part of the plant, and tissues 
 are predisposed to it by bruising, chilling, freezing, tip-burn, 
 sun-scald or aging. In the case of the southern bunch crops, 
 only the leaves are affected. It is prevalent in root crops 
 whenever tissues have been killed by exposure to extremely 
 wet conditions, by extremely high temperatures, or by freez- 
 ing. During rainy seasons, slimy soft rot may ruin southern 
 potatoes if they are not dug at once and dried. Future inves- 
 tigations may show that the slimy soft rot of the leafy parts, 
 and the soft mushy rot of the root or stem parts of plants, 
 well marked in carrots and cabbage, are not caused by the 
 same organism. The rot of the latter sometimes is called 
 the "true soft rot." In carrots that have been in storage, 
 soft rot is often found, the central tissue of the root being 
 most readily attacked. In the north, soft rot is common in 
 cabbage in the field late in the fall, especially where many 
 plants have been weakened or killed by the soil disease 
 known as cabbage yellows. Such rotted heads in the field 
 are a source of danger to sound stock since infection may be 
 carried on the knives used in cutting off the heads. This 
 may account for the common occurrence of the so-called 
 "stump rot" in cabbage in storage or transit. 
 
 Slimy soft rot occurs commonly in southern winter-grown 
 bunch crops. It results from infection in the field, in transit 
 or in storage, and develops and spreads under any of these 
 conditions. It is favored by the moist atmosphere prevail- 
 ing in iced barrels, crates, and hampers in which these crops 
 are shipped, and in the cellars and pits in which northern 
 stock, especially cabbage and celery and the root crops, are 
 stored. High temperatures are of even greater importance, 
 however, and greatly accelerate the progress of this rot, 
 especially in potatoes. 
 
MARKET DISEASES OF VEGETABLES. 21 
 
 Affected stock generally is not marketable, although 
 affected tissues can be trimmed away, leaving the sound 
 remainder salable. 
 
 The rot can be controlled by guarding against sun-scald, 
 freezing injury, and excessive bruising, by drying the sur- 
 faces of vegetables, especially those cut and bruised, and by 
 maintaining dry and cool conditions in transit and storage. 
 
 Ref. Carrot and other vegetables (33) ; cabbage (26) ; 
 lettuce (4), (36); onion (67). 
 
 WATERY SOFT ROT. 
 
 OF ASPARAGUS, BEAN, BEET, CABBAGE, CARROT, CAULIFLOWER, CELERY, 
 LETTUCE, KOHL-RABI, PEPPER, SALSIFY, SHALLOTS, SQUASH, TURNIP, 
 AND RUTABAGA. 
 
 Cause: A fungus (Sclerotinia). 
 
 This disease is a watery soft rot of the affected tissue 
 characterized by a white, cottony, at times matted, mycel- 
 ium; by the presence of hard masses or knots (sclerotia) 
 which are white at first and then become purplish black; 
 and by the absence of any offensive odor. 
 
 The watery disintegration associated with watery soft rot 
 is often so complete that water runs freely from crates, 
 hampers, and even cars containing affected stock. Due to 
 this loss of water, affected stock may shrink to but a small 
 portion of its original volume. 
 
 Affected tissue may seem only slightly discolored and 
 rotted, but upon application of pressure it is noted that the 
 tissue is completely softened and that water escapes with 
 the greatest ease. The slimy feeling noted in connection 
 with the slimy soft rot of succulent tissues is entirely absent. 
 
 The affected plants, the containers, and even the car may 
 be overrun by a heavy growth of loose, cottony or matted 
 mycelium, which under proper conditions forms the sclerotia 
 previously mentioned. The fungus often is responsible for 
 the so-called "nesting" of beans. 
 
 Affected celery tissue often has a pinkish or rose color, 
 especially in the early stages, and consequently the rot is 
 sometimes known as "pink rot" of celery. At times purplish 
 tints are noticeable. Generally, however, the diseased tissue 
 is yellowish or brown. 
 
 In typical field attacks upon lettuce, which are known as 
 lettuce "drop," or upon cabbage, the disease begins on the 
 stalk near the ground, or on the leaves touching the ground, 
 progressing from these to the stalk, which becomes softened 
 and at times entirely destroyed. The result in either case is 
 a collapse of the entire plant. In the field the disease is 
 known as "foot rot" of celery because of the frequent initial 
 attacks at the base of the plant. However, under storage 
 and transit conditions, plants may be attacked at any point. 
 Well headed cabbage or lettuce often remains intact be- 
 cause of the overlapping leaves. Often one finds, however, 
 when an attempt is made to lift an affected head, that it 
 
22 U. S. DEPARTMENT OF AGRICULTURE. 
 
 falls to pieces quite unlike plants affected with slimy soft 
 rot which tend to slip out of one's hand. 
 
 On root crops the rot is not as watery as on leafy tissues. 
 Under dry conditions, evaporation keeps pace with the 
 liberation of water by the fungus and the affected tissue 
 dries out and shrinks. Thus the watery nature of this rot in 
 roots is not as evident as in the case of leafy or succulent 
 tissues. However, under moist conditions, affected root 
 crops exude water freely. The white cottony or matted 
 mycelium and the black sclerotia serve to identify the dis- 
 ease on root crops when the watery characteristics are 
 absent. 
 
 This rot can be differentiated from slimy soft rot by the 
 fact that the latter is a slimy, slippery decay usually accom- 
 panied by a bad odor and lacks the white mycelium and 
 large sclerotia of watery soft rot. The latter can be differ- 
 entiated from gray mold rot by the typical powdery gray 
 moldy outgrowth of the latter. Gray mold rot is generally 
 found on overmature tissues, and is not as watery as the 
 typical watery soft rot caused by Sclerotinia. Watery soft 
 rot progresses at lower temperatures than does the soft rot 
 induced by Rhizopus. Rhizopus rot is prevalent in the sum- 
 mer and in overheated cars in the winter, while watery soft 
 rot develops in refrigerated cars. 
 
 The disease is favored by high humidity and moderate 
 temperatures. The original infection proceeds from the soil. 
 Lettuce grown under glass, or plants grown in crowded 
 quarters, are especially subject to infection. The disease 
 develops and spreads very rapidly in transit and storage, the 
 fungus passing from diseased to healthy tissue by contact. 
 
 Crop rotation and soil sanitation and aeration are control 
 measures which can be applied in the field. Losses in tran- 
 sit and storage may be reduced by sorting out and discard- 
 ing diseased plants and by thorough ventilation. After the 
 diseased portions of affected plants are trimmed off, the re- 
 mainder is edible. It is not advisable to store trimmed 
 plants. 
 
 Ref.: Lettuce (5); (65); (66). 
 
 SUN-SCALD. 
 
 OF CUCUMBER, HONEY DEW MELON, ONION, PEPPER, POTATO, TOMATO, 
 
 AND WATERMELON. 
 
 Cause : Exposure to the hot sun. 
 
 Sun-scald is evidenced by the death and discoloration of 
 a rather extensive area on the exposed surface of the vege- 
 table. In most cases, the lesion is irregular in outline and 
 at first resembles a water-soaked blister, but soon becomes 
 slightly but sharply sunken and distinctly bleached in color. 
 This bleaching is particularly noticeable in peppers, toma- 
 toes, and cucumbers. 
 
 Sun-scald is particularly important from the market 
 standpoint because the scalded areas are very subject to the 
 
MARKET DISEASES OF VEGETABLES. 23 
 
 attacks of rot-producing bacteria and fungi. On onions, 
 scald may be followed by slimy soft rot, and large losses 
 were thus incurred in certain shipments from Stockton, Cal., 
 in 1918. Tomato scald opens the way for fungous rots and 
 was an important factor in the losses in Texas and Tennessee 
 shipments in 1918. Sun-scalded muskmelons or water- 
 melons are frequently invaded by saprophytic fungi such as 
 black mold (Sterigmatocystis) and Cladosporium or Alter- 
 naria. Generally these are surface growths more or less 
 confined to the dead tissue. 
 
 Potato scald is discussed elsewhere, as is also sun-scald 
 of bean. 
 
 Because of its predisposition to rot during transit, scalded 
 stock could profitably be culled out before shipment. 
 
 NEMATODE DISEASE. 
 
 OF BEET, CARROT, CELERY, PARSNIP, POTATO, SWEET POTATO, RADISH, 
 RUTABAGA, AND TURNIP 
 
 Cause: A nematode or eelworm (Heterodera radicicola). 
 
 This disease affects the underground parts of plants. It 
 may be recognized on tubers by small, pimple-like swellings 
 or by larger protuberances of the surface, which ordinarily 
 becomes roughened at the infected places. These swellings 
 when some distance apart are circular, but if occurring close 
 together they take on various shapes and sizes. On roots 
 the disease appears as definite galls or knots and conse- 
 quently is commonly called root-knot. 
 
 Eelworm-infected tubers and roots sometimes are con- 
 fused with those affected by other diseases (crown-gall of 
 beets, club-root of crucifers, and "pimply potatoes" due to 
 flea-beetle injury), which also cause a swelling of the dis- 
 eased tissues. The nematode disease, however, may usually 
 be readily distinguished from other maladies by the pres- 
 ence of small, white; pear-shaped nematodes, the adult 
 females, which may barely be seen with the unaided eye 
 when well-infested tissues are broken or teased apart. 
 
 This disease occurs widely in most of the older trucking 
 sections of the southern portions of the United States and 
 in greenhouses everywhere. 
 
 Plants become infected in the field. The disease does not 
 develop or spread in transit or storage. Diseased stock, 
 however, is very subject to invasion by secondary organisms, 
 particularly bacteria. 
 
 Affected stock may largely be eliminated by grading. It 
 never should be shipped, not only because it is unsightly in 
 appearance, of inferior quality, and impaired in market 
 value, but also because it may carry the disease into unin- 
 fested regions. 
 
 Ref. (la). 
 
 ARTICHOKE: GRAY MOLD ROT; BOTRYTIS ROT. 
 
 (See Gray Mold Rot). 
 
24 U. S. DEPARTMENT OF AGRICULTURE. 
 
 ASPARAGUS: SLIMY SOFT ROT; BACTERIAL ROT. 
 
 (See Slimy Soft Rot). 
 
 ASPARAGUS: WATERY SOFT ROT; SCLEROTINIA ROT. 
 
 (See Watery Soft Rot) . 
 
 BEAN: ANTHRACNOSE. 
 
 Cause: A fungus (Colletotrichum lindemuthianum). 
 
 Anthracnose is marked in the very early stages by minute 
 oval or circular spots which are maroon to reddish in color. 
 These spots are not water-soaked as in the bacterial blight. 
 They form ulcer-like lesions, which increase rapidly in size 
 and, though circular, often coalesce to form large irregular 
 spots. Very soon, often in 24 hours, the spot becomes darker 
 in color, the central tissue dries up and shrinks, and a de- 
 pressed, considerably sunken spot results, with a black 
 center and generally a reddish border. Under moist con- 
 ditions the dark center of the spot becomes covered with 
 orange-pink dots or spore heaps which may run together 
 and form a slimy layer. These spore heaps are borne on 
 cushions known as acervuli (singular, acervulus). The bor- 
 der of the lesion is sharply marked, especially on the wax 
 pod varieties. 
 
 From pod lesions the fungus often enters the seeds. In 
 case of light attack the seed shows only a yellowish spot. 
 In severe cases the spots are yellowish, brownish, or black, 
 and circular or irregular in shape, and are surrounded by a 
 reddish zone. They may be sunken, but rarely show the 
 pinkish slime noted on the pod spots. The spots on the seed 
 are darker colored and more definitely marked than those 
 of bacterial blight. 
 
 Anthracnose occurs in all varieties of wax pod, green pod, 
 pole, navy, kidney, lima, and some scarlet runner beans. Its 
 development is favored by moderately cool weather, and its 
 spread, by wet weather. Since it is carried in the seed, the 
 disease may occur in any bean-growing section, but the 
 regions subject to cool, wet weather are most seriously af- 
 fected. It is least prevalent in the Rocky Mountain and 
 Pacific Coast States. 
 
 The original infection takes place in the field where both 
 the vines and pods are affected. The disease develops on 
 the pods in transit, and may spread under very moist con- 
 ditions. 
 
 Crop rotation and the use of disease-free seed or disease- 
 escaping varieties are the only known effective control 
 measures. Seed grown in hot, dry regions is comparatively 
 free from anthracnose. 
 
 Ref. (76); (14); (47). 
 
 BEAN: BACTERIAL BLIGHT. 
 
 Cause: Bacteria (Pseudomonas phaseoli). 
 
 In the early stages bacterial blight is marked by small, 
 
MARKET DISEASES OP VEGETABLES. 25 
 
 water-soaked spots on the pods. These gradually enlarge 
 and become irregular in shape, the green color fading as 
 the affected tissue dries out. The lesions may have an ele- 
 vated margin. Very soon th,e spots become reddish brown, 
 first at the margins and then in the centers. Finally they 
 turn a darker brown. In this stage the spot dries out and 
 becomes sunken. Under moist conditions, a slime oozes out 
 from the surface of the water-soaked spots. When dry, 
 this exudate forms a translucent or yellow crust. The bor- 
 der between healthy and diseased tissue is not as sharply 
 marked as in bean anthracnose, and is more irregular. The 
 presence of the exudate and the irregular shape of the lesion 
 usually serve to identify blight. 
 
 The bacteria from the pod lesions may penetrate and 
 infect the seeds. Such seeds are marked by yellow spots or 
 blotches of irregular shape or by surface crusts of a yel- 
 lowish color. These spots may show dark red borders and 
 at times a brown or black color. Seeds often are completely 
 yellowed and shriveled. 
 
 Bacterial blight occurs in all bean districts east of the 
 Rocky Mountains. Its spread is favored by moist warm 
 weather, though it can develop in dry weather. It causes 
 severe blighting of the foliage, and may kill plants outright. 
 Pod infection takes place in the field, but the spots may 
 develop or enlarge in transit, and may predispose the stock 
 to slimy soft rot or watery soft rot. 
 
 Blight is a seed-borne infection, and may be controlled 
 only by the use of disease-free seed and. the practice of crop 
 rotation. 
 
 Ref. (15); (75). 
 
 BEAN: SOIL ROT. 
 
 Cause: A fungus (Rhizoctonia). 
 
 Soil rot is characterized by large lesions generally near 
 the end of the pod or at points where the pod has been in 
 contact with the ground. The lesions are large and irregu- 
 lar in shape and light brown in color with soft, badly-rotted 
 underlying tissues. At times the spots are concentrically 
 marked. Anthracnose lesions are smaller and more regular 
 in shape. 
 
 Soil rot occurs only in very moist seasons. The original 
 infection takes place in the field. The fungus spreads from 
 diseased to healthy pods in transit under moist conditions 
 and often causes severe "nesting." The coarse, brown 
 hyphae of the fungus and the sclerotia, if present, distin- 
 guish soil rot from the watery soft rot induced by Sclero- 
 tinia and from the rot caused by Rhizopus, both of which 
 also cause "nesting." 
 
 Soil rot is controllable by careful sorting of the stock and 
 by maintaining a low temperature and humidity during 
 transit. 
 
26 U. S. DEPARTMENT OF AGRICULTURE. 
 
 BEAN: RUSSET. 
 
 Cause : Unknown. Non-parasitic. 
 
 Russet is a rather prevalent chestnut-brown surface dis- 
 coloration of green-pod and occasionally wax-pod beans. 
 The discolored areas are of various shapes and sizes, some- 
 times involving nearly all of the pod. The affected tissue 
 is firm and sound, and is not at all sunken. The discolora- 
 tion is due to the death of the three or four outer layers of 
 cells. 
 
 This disease seems to appear in beans that have been in 
 transit or storage for some time, and is probably not of field 
 origin. Russet is common in Florida beans in the northern 
 markets. It is objectionable because of the injury to the 
 appearance of affected stock. 
 
 No control is known. 
 
 BEAN: SUN-SCALD. 
 
 Cause : Exposure to the hot sun. 
 
 This injury first shows up on the exposed side of the pod 
 as minute brown or reddish parallel streaks, which enlarge 
 and merge to form brown or reddish areas of varying size. 
 Sun-scald is not easily distinguished from bacterial spot, but 
 is more likely to be limited to one side of the pod, and lacks 
 the greasy exudate which often is present on blight lesions. 
 
 Sun-scald is due to exposure to the sun, and does not 
 occur where the pods are shaded. 
 
 Ref. (41). 
 
 LIMA BEAN: POD BLIGHT. 
 
 Cause: A fungus (Diaporthe phaseolorum). 
 
 In the early stages, this disease is characterized by cir- 
 cular to semi-circular spots of darkened tissue. Later the 
 affected tissue becomes studded with minute, gray eleva- 
 tions. These elevations soon break the skin of the pod, and 
 emerge as black pustules, the fruiting bodies, or pycnidia, 
 of the fungus. The pycnidia may be arranged concentri- 
 cally or in chain-like fashion. In advanced stages, the entire 
 pod may become diseased and covered with pycnidia. 
 
 Pod blight has been reported only in the Northern Atlan- 
 tic States, and is not common. Infection takes place in the 
 field, and the disease may develop and progress in transit. 
 
 Pod blight can be controlled by seed selection and disin- 
 fection and by spraying in the field. It is advisable to sort 
 out and not market diseased pods. 
 
 Ref. (25). 
 
 BEAN: RHIZOPUS ROT. 
 
 (See Rhizopus Rot). 
 
 BEAN: SLIMY SOFT ROT; BACTERIAL ROT. 
 
 (See Slimy Soft Rot) . 
 
MARKET DISEASES OF VEGETABLES. 27 
 
 BEAN: WATERY SOFT ROT; SCLEROTINIA ROT. 
 
 (See Watery Soft Rot) . 
 
 BEET: BLACK ROT. 
 
 Cause: A fungus (Phoma betae). 
 
 In this rot, the affected tissue is coal black, rather firm 
 and extends deeply into the root. There is no bad odor. 
 The surface becomes somewhat shrunken, and often bears 
 the black pycnidia of the causal fungus. 
 
 This disease causes a leaf spot and a blight of the plants 
 in the field. The fungus is carried with the seed. 
 
 Control consists of seed and seed-bed sanitation and re- 
 moval of diseased leaves from roots previous to storage. 
 
 Ref. (17). 
 
 BEET: LEAF SPOT. 
 
 Cause: A fungus (Cercospora beticola). 
 
 This disease occurs only on the leaves where its lesions 
 appear as distinctly circular spots with purple borders and 
 tan to ashen gray centers. Leaves may be killed by the 
 coalescence of numerous lesions. The death of the older 
 leaves may cause the crown to elongate, thus affecting the 
 shape of the root. 
 
 Beet leaf spot is widespread in its occurrence and is of 
 considerable economic importance in the field. In the sugar 
 beet crop, it lowers the efficiency of the leaves as sugar pro- 
 ducers. In the market, leaf spot predisposes the leaves to 
 the attack of slimy soft rot. 
 
 Spraying with Bordeaux mixture will control the disease. 
 
 Ref. (40). 
 
 BEET: SLIMY SOFT ROT; BACTERIAL ROT. 
 
 (See Slimy Soft Rot). 
 
 BEET: GRAY MOLD ROT; BOTRYTIS ROT. 
 
 (Se&Gray Mold Rot). 
 
 BEET: WATERY SOFT ROT; SCLEROTINIA ROT. 
 
 (See Watery Soft Rot). 
 
 BEET: NEMATODE DISEASE. 
 
 (See Nematode Disease). 
 
 BEET: MISCELLANEOUS DISEASES. 
 ROOT ROT. 
 
 Cause: A fungus (Rhizoctonia). 
 
 This rot starts typically from the crown, and progresses 
 downward from the leaf bases. 
 Ref. 417). 
 
 SCAB. 
 
 Cause: A fungus (Actinomyces scabies). 
 
28 U. S. DEPARTMENT OF AGRICULTURE. 
 
 Beet scab closely resembles potato scab. Large corky 
 brown excrescences are produced. Sugar beets and mangels 
 are susceptible. 
 
 This disease is uncommon in the market. 
 
 BRUSSELS SPROUTS: BLACK LEAF SPOT. 
 
 (See Cabbage Black Leaf Spot) . 
 
 BRUSSELS SPROUTS: RING-SPOT. 
 
 (See Cauliflower Ring-Spot). 
 
 CABBAGE: BLACK LEAF SPOT. 
 
 Cause: A fungus (Alternaria brassicae). 
 
 In the early stages, this disease is characterized by 
 minute, circular, shiny, brown to black spots. Later these 
 spots enlarge and lose their circular shape. The lesions 
 generally are somewhat concentrically marked in target 
 fashion and, under moist conditions, may be covered by a 
 growth of brown to black mold. Generally, if affected heads 
 are kept in a dry place, the centers of the spots fall out and 
 leave holes. 
 
 The lesions are more pronounced and more common on 
 the outer leaves, but under moist conditions, the fungus may 
 penetrate from leaf to leaf and often may afford points of 
 attack for the bacteria of slimy soft rot. 
 
 Infection occurs in the field, and the disease develops in 
 transit and storage. 
 
 Disinfection of storage houses, care in handling, and a 
 regulation of temperature and moisture conditions will con- 
 trol the disease in storage. The spots do not render cabbage 
 unfit for transit and storage if the affected leaves are 
 trimmed off. 
 
 Ref. (26). 
 
 CABBAGE: BLACK ROT. 
 
 Cause: Bacteria (Pseudomonas campestris). 
 
 Black rot is characterized by a black discoloration of the 
 water-conducting tissue of the plant. Sometimes the dis- 
 coloration occurs only as a ring in the stalk, but not infre- 
 quently it extends into the leaf midrib and veins. This 
 discoloration in the stalk can be seen easily if a fresh section 
 is cut, and its progress into the leaves can be noted by break- 
 ing the leaves from the stem, which will reveal a group of 
 black dots in the leaf scars. Badly affected leaves have a 
 steel gray or purplish hue, due to partial masking of the 
 blackened veins by the white or yellowish leaf tissue. 
 
 If no secondary rots set in, the disease may show itself 
 as a slowly progressing rot which does not necessarily pro- 
 ceed from the outside leaves as in slimy or watery soft rot, 
 but may appear in the covered leaves, even in the heart of 
 the head. Generally, however, a typical slimy soft rot sets 
 
MARKET DISEASES OF VEGETABLES. 29 
 
 in, proceeding either from the outside or inside, and the 
 head rots rapidly with a very offensive odor.. 
 
 This disease occurs in all cabbage-growing regions. Infec- 
 tion takes place in the field. The bacteria enter the plant 
 at the margins of the leaves, proceed downward through 
 the veins to the main stalk, and then upward into the head. 
 
 The disease develops in transit and storage. Affected 
 stock is very subject to secondary rots, and as a result is a 
 menace to healthy stock. 
 
 Control of the disease in the field consists of seed disin- 
 fection, seedbed sanitation, and crop rotation. Severely 
 affected stock is unfit for food. It is not advisable to store 
 or ship slightly affected stock. 
 
 Ref. (61); (26). 
 
 CABBAGE: FREEZING INJURY. 
 
 Cause : Exposure to low temperatures. 
 
 Freezing injury is marked by a glassy yellowish appear- 
 ance of the affected tissues. 
 
 Affected stock, if thawed rapidly in a warm place, or if 
 kept in a moist atmosphere, is soon destroyed by slimy soft 
 rot. Therefore it is not suitable for storage. It is generally 
 assumed that cabbage can be frozen once or twice, if thawed 
 out properly, without any injury except a slight shrinkage 
 and flabbiness. The outer leaves can be frozen and thawed 
 without injury, but if the freezing extends to the interior 
 tender tissues, these are killed and, upon thawing, fall a 
 ready prey to slimy soft rot. 
 
 Generally all frozen heads which do not show a glassy, 
 yellowish ring in the tissue of the stalks upon thawing are 
 fit for marketing for immediate consumption. This is not 
 a positive test, however, since not all affected heads show 
 a discoloration or decay of the stalk. 
 
 CABBAGE: LEAF SPECK. 
 
 Cause : Not known ; probably non-parasitic. 
 
 Leaf speck consists of small, sharply-sunken, shiny, brown 
 spots or black specks which may occur on all leaves of an 
 affected head. Speck can be differentiated from black leaf 
 spot by the smaller size of the spots, and by the absence of 
 concentric rings, or any black fungous outgrowth. 
 
 Leaf speck occurs in cabbage from all sections, and is very 
 severe in some Florida stock. 
 
 Nothing is known about the cause, point of origin, and 
 conditions favoring the development of the disease. 
 
 No control measures are known. It is advisable to sort 
 cabbage carefully because affected heads have a lower 
 market value. 
 
 CABBAGE: SUN-SCALD. 
 
 (See Sun-Scald). 
 
30 U. S. DEPARTMENT OF AGRICULTURE. 
 
 CABBAGE: GRAY MOLD ROT; BOTRYTIS ROT. 
 
 (See Gray Mold Rot) . 
 
 CABBAGE: RHIZOPUS ROT. 
 
 (See Rhizopus Rot). 
 
 CABBAGE: SLIMY SOFT ROT; SOFT ROT; BACTERIAL ROT. 
 
 (See Slimy Soft Rot) . 
 
 CABBAGE; WATERY SOFT ROT; SCLEROTINIA ROT. 
 
 (See Watery Soft Rot). 
 
 CARROT: GRAY MOLD ROT; BOTRYTIS ROT. 
 
 (See Gray Mold Rot and Artichoke Gray Mold Rot) . 
 
 CARROT: RHIZOPUS ROT. 
 
 (See Rhizopus Rot) . 
 
 CARROT: SLIMY SOFT ROT; SOFT ROT. 
 
 (See Slimy Soft Rot) . 
 
 CARROT: WATERY SOFT ROT; SCLEROTINIA ROT. 
 
 (See Watery Soft Rot). 
 
 CARROT: NEMATODE DISEASE. 
 
 (See Nematode Disease). 
 
 CAULIFLOWER AND BRUSSELS SPROUTS: RING-SPOT. 
 
 Cause: A fungus (Mycosphaerella brassicicola). 
 
 The symptoms of this disease of cauliflower are small 
 definitely circular spots on the leaves. They are visible on 
 both sides of the leaf, have light brown or grayish, dry 
 centers, and are surrounded by olive-green or blue-green 
 borders which shade off into the natural color of the leaf. 
 When the leaves turn yellow, the spots retain their green 
 borders and become very conspicuous against the yellow 
 background. The borders of the lesions are frequently 
 raised, and may show concentric circles. Very minute, 
 black dots, pycnidia, cover the outer edges of the spots on 
 both surfaces of the leaves. They are densely crowded in 
 the outer parts of the lesions, but are more scattered or 
 absent in the centers of the spots. 
 
 Ring-spot is a field disease on the Pacific Coast. Infec- 
 tion takes place in the field, but the lesions may develop 
 and enlarge during transit. 
 
 This disease causes premature yellowing and death of 
 the leaves and thus affects the quality of the stock. 
 
 Ref. (52). 
 
MARKET DISEASES OF VEGETABLES. 31 
 
 CELERY: BACTERIAL LEAF SPOT. 
 
 Cause: Bacteria. 
 
 This disease is characterized by shiny, dark-brown irregu- 
 lar, translucent or parchment-like spots on the leaves. 
 Often these lesions extend along the veins and down the 
 petioles causing a water-soaked condition. This disease 
 causes a premature yellowing and death of the leaves. The 
 lesions of this disease can be differentiated from the early 
 blight lesions by the ashen gray, opaque centers of the 
 latter and from late blight lesions by the absence of the 
 black shiny dots or pycnidia. 
 
 Bacterial leaf spot occurs in Michigan and New York 
 celery. 
 
 Infection takes place in the field and the disease may 
 develop, but does not spread in transit or storage. 
 
 Severely affected stock is discriminated against because 
 of its unsightliness and because the petiole lesions destroy 
 the edible parts of the plant. 
 
 Spraying with Bordeaux will control the disease. 
 
 CELERY: EARLY BLIGHT. 
 
 Cause: A fungus (Cercospora apii). 
 
 Early blight is characterized by irregular, slate-colored 
 spots on the leaves, with ashen-gray to tan centers. These 
 can be distinguished from late blight lesions by their larger 
 size and the absence of the conspicuous black dots or 
 pycnidia. Generally early blight occurs only on the leaves, 
 while late blight occurs very commonly on the petiole as 
 well as on the leaf blade. At times early blight occurs on 
 the petioles as elongated, tan, sunken areas, and causes a 
 wilting and drying out of the leaf and petiole. This disease 
 occurs in all celery districts, but is most common in Florida 
 celery. It is favored by hot, dry weather. 
 
 Early blight starts as a field infection, and develops in 
 transit or storage. Unlike late blight, it does not lead to a 
 rot, but causes the tissues to dry out and shrivel. 
 
 Severely affected stock is unsightly and its market value 
 is reduced. 
 
 Early blight can be controlled by spraying with Bordeaux 
 mixture. 
 
 CELERY: GRAY MOLD ROT; BOTRYTIS ROT. 
 
 (See Gray Mold Rot). 
 
 CELERY: LATE BLIGHT. 
 
 Cause: A fungus (Septoria petroselini) . 
 
 Late blight is characterized by small, irregular, brown 
 spots on the leaf blade and petiole. Under transit condi- 
 tions, the lesions may be dark green and water-soaked. 
 The centers of the spots bear small, black, glistening dots, 
 the fruiting bodies or pycnidia of the fungus. This disease 
 
32 U. S. DEPARTMENT OF AGRICULTURE. 
 
 can be differentiated from early blight and bacterial leaf 
 spot by the presence of the shiny pycnidia and the more 
 common occurrence of spots on the petioles, where the 
 pycnidia are even more conspicuous than on the leaf lesions. 
 
 This disease occurs generally in all celery districts, espe- 
 cially in California, Florida, Michigan, and New York. It 
 is favored by cool, moist weather. 
 
 The fungus overwinters on the seed and in the soil. Late 
 blight spreads in the field during the growing season, and 
 although the original infection takes place in the field, the 
 disease develops and spreads in transit and storage, leading 
 to a soft rot of the leaf blades and petioles. 
 
 Severely affected stock is unfit for market and storage 
 purposes. 
 
 Crop rotation, use of disease-free seed, and proper spray- 
 ing will control the disease. It is advisable to discard 
 severely diseased plants because of the continued develop- 
 ment of the disease at low temperatures. 
 
 Ref. (11); (55). 
 
 CELERY: SLIMY SOFT ROT; BACTERIAL ROT. 
 
 (See Slimy Soft Rot) . 
 
 CELERY: WATERY SOFT ROT; SCLEROTINIA ROT; FOOT ROT; 
 PINK ROT; RIB ROT. 
 
 (See Watery Soft Rot) . 
 
 CELERY: BLACK HEART. 
 
 Cause : Unbalanced water relations. 
 
 In the earliest stages this .disease is marked by shiny, 
 light brown lesions on the blades of the youngest leaves. 
 Very often these are not apparent until the heart of the 
 plant is dissected, since the innermost, most completely pro- 
 tected leaves frequently are the only ones affected. Later 
 the lesions enlarge so as to involve the entire leaf blade, and 
 become very moist and turn black, the whole heart, even 
 the entire stalk, becoming involved if sufficient time is 
 allowed. The advanced symptoms of the disease are caused 
 by bacteria of the Bacillus caratovorus type, which invade 
 the tissue killed by the unbalanced water relations of the 
 plant. 
 
 Black heart originates in the field. Its evil consequences 
 are so well realized by shippers that most affected stock is 
 culled out before shipping. Whether or not stock will de- 
 velop black heart depends upon the plant itself, upon the 
 nature of the soil on which the crop is grown, and upon the 
 weather. In Florida the disease is most severe in late season 
 plants of the Golden Heart variety. 
 
 Ref. (60). 
 
 CELERY: NEMATODE DISEASE. 
 
 (See Nematode Disease). 
 
MARKET DISEASES OF VEGETABLES. 33 
 
 CUCUMBER AND MUSKMELON; ANTHRACNOSE. 
 
 Cause: A fungus (Colletotrichum lagenarium). 
 
 On cucumbers the anthracnose lesions are found in the 
 market as circular, sunken, water-soaked spots which 
 usually bear a slimy, orange-pink coating of spore masses. 
 As the rotted tissue dries out, the surface may crack. 
 
 On Honeydew muskmelons the oval, light gray lesions 
 with concentric rings of pink or black dots (acervuli) are 
 very conspicuous. Large lesions become sunken, and the 
 central tissue often cracks open, affording a port of entry 
 for other fungi. 
 
 On netted cantaloupes, the lesions are sharply sunken but 
 not very conspicuous until the salmon-colored spore masses 
 appear. 
 
 The same fungus causes anthracnose of watermelon (dis- 
 cussed elsewhere). 
 
 Anthracnose is a field disease occurring on leaves, stems, 
 and fruits. Infection proceeds from infested seed or soil, 
 and the disease spreads during wet weather. Fruit infec- 
 tion takes place in the field and the lesions enlarge in transit, 
 causing serious blemishing. Frequently, secondary rots 
 enter through the anthracnose spots. 
 
 Anthracnose is of widespread occurrence. In the market 
 it has been noted commonly on Louisiana cucumbers and 
 Colorado Honeydew and Osage muskmelons. 
 
 Affected fruits are unsightly and rapidly become un- 
 salable. 
 
 The disease can be controlled by crop rotation, use of 
 disease-free seed, and spraying with Bordeaux mixture. It 
 is advisable not to ship fruits showing any signs of the dis- 
 ease because of its rapid development in transit. 
 
 Ref. (21). 
 
 CUCUMBER: BACTERIAL SPOT. 
 
 Cause: Bacteria (Bacterium lachrymans). 
 
 The lesions of bacterial spot appear as small greasy or 
 water-soaked spots, usually showing a small whitish dot in 
 the center. The diseased spots may enlarge and lead to a 
 secondary soft rot of rather large areas. Often a jelly-like 
 mass of exudate is formed on these lesions. Under certain 
 conditions, such rotted tissue may dry out, leaving cavities 
 in the surface of the fruit. 
 
 Bacterial spot is a common and widespread disease of the 
 vines causing what is known in the field as angular leaf spot. 
 The disease is carried with the seed and spreads in the field 
 in wet weather. Fruits become infected in the field, and the 
 disease may progress but does not spread during transit. 
 
 The disease may be controlled by seed disinfection, crop 
 rotation, and spraying with Bordeaux mixture. 
 
 Ref. (6); (62); (8). 
 
34 U. S. DEPARTMENT OF AGRICULTURE. 
 
 CUCUMBER: MOSAIC. 
 
 Cause : Unknown. 
 
 Cucumbers affected with mosaic may be variously mis- 
 shapen, often bearing large warts. They are often dis- 
 tinctly mottled in color. A common type is a combination 
 of green warts on a white or yellowish background. 
 
 Mosaic is a widespread and very destructive disease of 
 the vines which greatly reduces the yield. It is extremely 
 communicable and is spread by insects. 
 
 Usually the more severely affected fruits do not reach the 
 market. So far as known, the edibility and keeping quali- 
 ties of affected fruits are not impaired, but the market value 
 is materially lowered. 
 
 No practical control is known. 
 
 Ref. (13); (22); (31). 
 
 CUCUMBER: SCAB. 
 
 Cause: A fungus (Cladosporium cucumerinum). 
 
 The symptoms of this disease on the fruits are small, cir- 
 cular, sunken lesions covered with a greenish velvety 
 growth of mold. Drops of a red gummy exudate may be 
 formed on these spots. The disease is not simply a scab as 
 the name would imply, since the tissues are rather deeply 
 involved. 
 
 The fungus attacks the vines, and fruit infection occurs 
 in the field. Young growing parts are very subject to 
 attack. The disease is very important in the pickle crop, 
 where it becomes severe late in the season. It is favored 
 by cool, moist weather. 
 
 Ref. (12). 
 
 CUCUMBER: SUN-SCALD. 
 
 (See Sun-Scald). 
 
 EGG PLANT: FRUIT ROT. 
 
 Cause: A fungus (Phomopsis vexans). 
 
 At first fruit rot consists of small, circular or oval spots. 
 Usually the lesions are at first much lighter in color (tan or 
 gray) than the surrounding tissue. Later the lesions become 
 dark brown and sunken, and under favorable conditions 
 increase very rapidly in size. By the coalescence of such 
 lesions, much or all of the surface of a fruit may be involved. 
 Small, brown to black, pimple-like pustules or pycnidia 
 break through the surface and cover the inner and older 
 zones of affected tissue. The affected regions are brown 
 and softened. At times they are quite dry, suggesting a 
 dry rot. 
 
 Fruit rot occurs in all egg plant growing regions, but is 
 especially severe in the South. 
 
 The disease occurs on the plants in the field, where it 
 attacks leaves, stems, and fruit, and is known as leaf spot, 
 
MARKET DISEASES OF VEGETABLES. 35 
 
 stem blight, and fruit rot. The original infection of the fruit 
 takes place in the field, but the disease develops and spreads 
 in transit and often causes heavy losses. 
 
 It is not safe to ship spotted fruits. 
 
 Ref. (23). 
 
 EGG PLANT: RHIZOPUS ROT. 
 
 (See Rhizopus Rot). 
 
 LETTUCE: BLACK ROT. 
 
 Cause : Bacteria. 
 
 Black or brown spots or irregular patches on the outer 
 leaves, increasing in size under proper conditions until entire 
 leaves are involved, are the symptoms of this disease. Later 
 the inner leaves may be attacked, and a soft dark brownish 
 rot of the head may result. 
 
 This is a field disease reported from Florida affecting 
 seedlings and older plants. It may develop during transit. 
 
 Other bacterial field diseases of lettuce have been re- 
 ported from North Carolina and Louisiana. 
 
 The relation of these field diseases to the slimy soft rot 
 prevalent in the market has not yet been determined. 
 
 Ref. (60). 
 
 LETTUCE: GRAY MOLD ROT; BOTRYTIS ROT. 
 
 (See Gray Mold Rot and Cauliflower Gray Mold Rot). 
 
 LETTUCE, ENDIVE, ESCAROLE, AND CHICORY: SLIMY SOFT 
 ROT; BACTERIAL ROT. 
 
 (See Slimy Soft Rot). 
 
 LETTUCE: WATERY SOFT ROT; SCLEROTINIA ROT; DROP; 
 
 DAMP-OFF. 
 
 (See Watery Soft Rot). 
 
 LETTUCE: RUSSET. 
 
 Cause : Not known, probably non-parasitic. 
 
 This disease is characterized by small reddish to russet 
 spots or streaks which may occur on practically all of the 
 leaves of an affected head. The brown streaks usually occur 
 along the large veins of the leaves. The vascular bundles 
 in the stalk and in the petioles may also be discolored. 
 
 Russet occurs in lettuce from all regions. 
 
 Nothing is known about control of the disease. 
 
 It is advisable to sort carefully before shipping because 
 the presence of russeted heads reduces the value of a ship- 
 ment. 
 
 LETTUCE: TIP BURN. 
 
 Cause: Non-parasitic (irregular water supply). 
 
 This disease is characterized by the dead, brown borders 
 
36 U. S. DEPARTMENT OF AGRICULTURE. 
 
 of the leaves throughout the head. It is found in head let- 
 tuce from all except the Boston district. 
 
 Tip burn is a field disease probably caused by an irregular 
 water supply. The injury is most likely to occur when 
 bright warm weather follows a period of cloudy or rainy 
 weather, and is much worse on certain soils than on others. 
 The disease seems to be least prevalent on a soil with a high 
 sand and low clay content, combined with a high water- 
 holding capacity. In such a soil, lettuce becomes deep 
 rooted, and can apparently obtain water with sufficient 
 rapidity to prevent injury from too rapid transpiration. In 
 the Imperial Valley of California, this disease appears to be 
 associated with an excess of alkali in the soil. 
 
 Tip burn often predisposes affected stock to slimy soft rot 
 during transit and storage. The slimy soft rot starts in the 
 dead tissues, especially in the interior of the head where 
 moist conditions prevail. Sometimes the rot gets a foothold 
 even in the growing plant. 
 
 No effective method of control has been established for 
 tip burn. A well-regulated water supply and the use of 
 varieties properly adapted to the soil and climatic condi- 
 tions are important considerations. 
 
 Ref. (19); (20). 
 
 LETTUCE: MISCELLANEOUS DISEASES. 
 DOWNY MILDEW. 
 
 Cause: A fungus (Bremia lactucae). 
 
 The symptoms of this disease are sharply angular leaf 
 spots, yellowish to brown when viewed from above, and 
 bearing on the lower surfaces a white felt-like outgrowth of 
 mold, the spores and spore-bearing mycelium of the fungus. 
 
 Downy mildew occurs on lettuce grown under glass and 
 on the field crop where moist cool weather prevails, as in 
 the Colma district in California. In head lettuce, the inner 
 as well as outer leaves are attacked. This disease is of some 
 importance because of its direct attack on the edible leaves 
 and because of its tendency to predispose the tissues to slimy 
 soft rot. 
 
 LEAF SPOT. 
 
 Cause : A fungus (Septoria consimilis) . 
 
 This disease causes brown spots on the older leaves bear- 
 ing black points, the pycnidia of the fungus. It occurs on 
 garden varieties late in the season, and is of little impor- 
 tance. 
 
 LEAF SPOT. 
 
 Cause: A fungus (Cercospora lactucae). 
 
 Small tan-colored spots on the older leaves are the symp- 
 toms of this disease, which has been noted in the San Fran- 
 cisco market. 
 
 SHOT HOLE OR ANTHRACNOSE. 
 
 Cause: A fungus (Marssonia panattoniana). 
 
MARKET DISEASES OF VEGETABLES. 37 
 
 Small brown spots on the leaves, from which the dry cen- 
 ters often crack and fall out, are characteristic of this dis- 
 ease, which occurs on greenhouse lettuce. 
 
 Ref. (2). 
 
 MUSKMELON: (HONEYDEW AND CASABA): FRUIT SPOT. 
 
 Cause: A fungus (Alternaria). 
 
 On Honeydew melons, this disease appears first as small 
 water-soaked or chestnut-brown spots on the surface. As 
 these enlarge, they become more oval in shape and may 
 have wide water-soaked borders. Later the lesions become 
 more or less sunken and usually develop black centers. 
 Under humid conditions a velvety surface growth of mold is 
 produced on the lesions. This mold is at first gray, but soon 
 becomes dark greenish gray and later dark brown or almost 
 black. 
 
 Continued development and coalescence of these lesions 
 lead to an extensive shallow rot of the rind accompanied by 
 a cracking of the surface. The affected tissue is at first very 
 soft and watery, later becoming yellowish and very dry, 
 tough, and leathery. The rot eventually penetrates through 
 the rind into the edible pulp below. 
 
 The symptoms on the Casaba melon are essentially similar 
 to those on the Honeydew melon. On the striped Christmas 
 Casaba melon, the lesions are brown and less conspicuous 
 and the surface growth of mold is not common. 
 
 Fruit spot lesions differ from those of anthracnose in the 
 absence of acervuli and in the moldy outgrowth usually 
 present. 
 
 This disease was found very prevalent during the fall of 
 1918 on Colorado Honeydew melons, and on both the Ca- 
 saba and Christmas Casaba melons from Turlock, Cal. 
 
 The source of infection is not known. The lesions appear 
 during transit and storage and become very conspicuous in 
 the market, not only detracting from the appearance of the 
 melons but also causing an objectionable surface rot. In 
 addition, the lesions also serve as points of entry for other 
 rot-producing organisms. 
 
 No control measures are known. 
 
 MUSKMELON: SUN-SCALD. 
 
 (See Sun-Scald). 
 
 MUSKMELON (CANTALOUPE): MISCELLANEOUS DISEASES. 
 BACTERIAL SOFT ROT. 
 
 Cause : Bacteria. 
 
 Wounds and fruit spot lesions may open the way for the 
 entrance of bacteria which cause a soft rot of the tissues. 
 This rot is very soft and mushy and the tissue appears water- 
 soaked. , 
 
 FUSARIUM ROT. 
 
 Cause: A fungus (Fusarium). 
 
38 U. S. DEPARTMENT OF AGRICULTURE. 
 
 This is a rapidly progressing rot usually characterized 
 externally by a dense and profuse outgrowth of pinkish 
 white mold. The rotted tissue is rather dry, and the pink 
 mycelium may cause the entire rotted area to appear pinkish 
 in color. Other types of Fusarium rots may occur in the 
 field. These rots progress more rapidly than the rot caused 
 by Alternaria. 
 
 GREEN MOLD ROT. 
 
 Cause: A fungus (Cladosporium). 
 
 This disease occurs very frequently on cantaloupes after 
 they have been in transit a long time. It is characterized 
 by a green, velvety fungous growth, which causes a slowly 
 progressing rot. 
 
 MUSKMELON (CANTALOUPE AND HONEYDEW): 
 ANTHRACNOSE. 
 
 (See Cucumber Anthracnose). 
 
 MUSKMELON (HONEYDEW): BLACK MOLD ROT. 
 
 Cause: A fungus (Alternaria). 
 
 This is marked by a brown to black, velvety surface 
 growth of the fungus. The fungus usually invades tissue 
 killed by sun-scald and causes a rot of the underlying tissues. 
 This rot is also very common on watermelons affected by 
 sun-scald. 
 
 ONION: BLACK MOLD ROT. 
 
 Cause : A fungus (Sterigmatocystis niger) . 
 
 Black mold is characterized by black, powdery masses on 
 or between the scales. When these masses occur between 
 the scales they have a tendency to follow the veins. 
 
 Affected stock may show no symptoms other than the 
 presence of this black powder. At times sunken and dis- 
 colored areas are found underlying the powdery black 
 masses. Under dry conditions the affected tissue is papery 
 and brittle and sometimes highly colored. 
 
 Although commonly called "smut," this disease should 
 not be confused with true smut. The latter is rarely found 
 on the market except on sets, and is marked by black, pow- 
 dery masses within the scale tissues. 
 
 All varieties of onions are susceptible. The disease is 
 very common on California and Texas onions. Infection 
 occurs in the field, though the fungus continues to grow in 
 storage. 
 
 As a rot, this disease under dry conditions usually is of 
 minor importance, but as a blemish it causes very serious 
 depreciation in value of the affected stock. Under moist 
 conditions the fungus may cause severe rotting. 
 
 Since this disease does not progress very rapidly, affected 
 bulbs can probably be held for some time if they are kept 
 
MARKET DISEASES OF VEGETABLES. 39 
 
 in very dry storage at 32 to 35 F., preferably in slatted 
 crates rather than in bags. 
 Ref. (74). 
 
 ONION: GRAY MOLD ROT; BOTRYTIS ROT. 
 
 (See Gray Mold Rot). 
 
 ONION: NECK ROT. 
 
 Cause: Fungi (Botrytis; Sclerotium). 
 
 This is a semi-watery rot followed by a shrinking and 
 shriveling of the scales. The rot occurs typically as a neck 
 rot in the field, while in storage other regions of the bulb 
 also may be attacked. A gray moldy growth and hard, 
 grayish to black masses of the fungus (sclerotia) develop 
 on the outside of the scales. Neck rot is an example of the 
 gray mold rot of vegetables elsewhere described. 
 
 Neck rot has a tendency to rot all scales uniformly down- 
 ward rather than to follow certain scales as does slimy soft 
 rot. Typical neck rot is especially conspicuous in white 
 onions. In red and yellow varieties, the infection may be 
 confined to the inner scales, and external neck rot symptoms 
 may be lacking. In colored varieties, the soft rotted condi- 
 tion is often found, and the diseased flesh frequently be- 
 comes pinkish, but the gray mold growth and sclerotia are 
 less commonly found. Unlike slimy soft rot, neck rot does 
 not have a foul odor. 
 
 Infection takes place in the field, at or shortly after the 
 harvest. The fungus enters the cut necks of bulbs, and 
 gradually progresses downward. The rot develops in stor- 
 age under moist conditions. Chilled or frozen onions and 
 scallions are subject to neck rot. In chilled onions, the rot 
 is more frequent in places other than the neck. 
 
 If onions show a high percentage of neck rot in storage, 
 transit, or market, disposal for immediate consumption is 
 advised. 
 
 The disease can be controlled by prompt curing of the 
 crop and by storage in a dry place at 32 to 35 F. It is 
 destructive in onion sets as well as in table stock. 
 
 Ref. (48). 
 
 ONION: SLIMY SOFT ROT. 
 
 Cause: Bacteria (Bacillus carotovorus group). 
 
 This is a very soft, mushy rot of the scales, which pro- 
 gresses downward from the neck and is accompanied by a 
 very repulsive odor. Often it is confined to only one or two 
 scales in the interior of the bulb. Lesions may occur any- 
 where, however, especially if the tissues have been killed 
 by sun-scald or bruising. 
 
 Slimy soft rot progresses faster than neck rot, and is not 
 accompanied by a gray mold and sclerotia as is neck rot. 
 Neither does it progress uniformly downward destroying all 
 
40 U. S. DEPARTMENT OF AGRICULTURE. 
 
 scales as does neck rot, but usually follows certain scales 
 all the way around. 
 
 Slimy soft rot occurs in all onion-growing districts in the 
 United States, and is most common in onions harvested dur- 
 ing warm, rainy seasons, or in onions sun-scalded during the 
 curing process. It is also very common in Spanish onions. 
 It is claimed by growers that yellow varieties are more sus- 
 ceptible than red. Careful handling to avoid sun-scald and 
 bruising during the harvesting operation is of primary im- 
 portance as a preventive measure. 
 
 In badly affected shipments, immediate drying of the 
 stock will check the progress of the rot. This may be done 
 by dumping the sacks at once and spreading the contents. 
 
 Ref. (67). 
 
 ONION: SMUDGE. 
 
 Cause: A fungus (Colletotrichum circinans). 
 
 Smudge or anthracnose is a disease of white onions char- 
 acterized by black blotches or aggregations of minute black 
 dots on the outer scales. Each one of the minute dots is an 
 acervulus (plural, aceryuli). These acervuli are often ar- 
 ranged in concentric rings. In severe cases, the smudgy 
 spots are so extensive that the side of the onion appears 
 smoked. Generally the smudge is on the outside scales, 
 though it may appear on the inner scales as well. It should 
 not be confused with the black powder which is character- 
 istic of black mold. 
 
 It is of widespread geographic distribution, but only white 
 varieties are seriously affected. Infection takes place in 
 the field from the fungus which overwinters in the soil. The 
 disease appears shortly before the harvest, and develops 
 rapidly in the crated onions after the harvest if the weather 
 is moist. It causes very little shrinkage of affected bulbs, 
 the chief damage being due to the appearance and reduced 
 market value of affected bulbs. 
 
 Smudge can be prevented by rapid curing of the crop as 
 soon as it is harvested. If the bulbs are stored in a dry place, 
 the disease makes little progress. In a moist atmosphere, 
 the fungus penetrates from scale to scale, and causes a soft- 
 ening of the tissues. 
 
 Ref. (72). 
 
 ONION: SMUT. 
 
 Cause: A fungus (Urocystis cepulae). 
 
 Onion smut appears as dark-colored, slightly raised 
 streaks or blisters on the bulbs and leaves. The leaves are 
 often recurved and distorted. Sets may be greatly shrunken 
 with the whole exterior covered with the blisters. When cut 
 open, these ridges or pustules are found to be filled with a 
 greenish black powdery mass. Smut differs from black mold 
 in that the black powder is within the tissues of the scale, 
 not upon or between the scales. 
 
MARKET DISEASES OF VEGETABLES. 41 
 
 Onion smut is common in northern growing regions, espe- 
 cially in Wisconsin, Illinois, New York, Ohio, Iowa, and 
 Massachusetts. 
 
 The fungus persists in the soil, and infection occurs when 
 the plants are seedlings. Badly infected plants are usually 
 killed and large losses are thus caused in the field. There 
 is no progress of the disease in storage or transit. Smut is 
 uncommon in the market except on onion sets. 
 
 Control measures are planting in clean soil or the use of a 
 formaldehyde drip on the seed drill. 
 
 Ref. (71). 
 
 ONION: MISCELLANEOUS DISEASES. 
 
 BLOTCH. 
 
 Cause: A fungus (Macrosporium). 
 
 The name "blotch" has been temporarily adopted for this 
 blemish on the outer scales of red and yellow varieties of 
 onions. The symptoms are large bleached or greenish dis- 
 colored areas on the bulbs, bearing numerous fine black 
 linear marks or ridges parallel to the veins. 
 
 BLUE MOLD. 
 
 Cause: A fungus (Penicillium). 
 
 Under certain conditions in storage or transit, blue mold 
 occurs on the outside of the bulbs, and is usually associated 
 with insufficient ventilation and some predisposing injury to 
 the tissues, such as wounds, freezing, or sun-scald. 
 
 While most fruits are subject to attack by species of Peni- 
 cillium, among vegetables, only onions, sweet potatoes and 
 sweet corn are commonly attacked. 
 
 FUSARIUM ROT. 
 
 Cause: A fungus (Fusarium). 
 
 This rot usually but not always proceeds from the base 
 of the bulb. The affected region is soft and flabby and be- 
 comes shrunken and shriveled in appearance. The surface 
 may be studded with small white pads, the fruiting bodies 
 of the causal fungus. There is no development of gray mold 
 or black sclerotia as in neck rot. 
 
 GRAY MOLD SPOT. 
 
 Cause: A fungus (Botrytis). 
 
 This disease causes a bright red lesion on the neck at the 
 ground line, which results in the death of the outer leaf. At 
 times a slight outgrowth of gray mold may be formed in the 
 lighter colored center of the lesion. Gray mold spot is found 
 only on winter-grown green onions in the spring, and has 
 been noted in the Kansas City market gardens. 
 
 SUN-SCALD. 
 (See Sim-Scald). 
 
42 U. S. DEPARTMENT OF AGRICULTURE. 
 
 PARSNIP: GRAY MOLD ROT; BOTRYTIS ROT. 
 
 (See Gray Mold Rot). 
 
 PARSNIP: WATERY SOFT ROT; SCLEROTINIA ROT. 
 
 (See Watery Soft Rot). 
 
 PEA: BACTERIAL SPOT. 
 
 Cause : Bacteria. 
 
 On the pods this disease appears as greasy water-soaked 
 spots which may enlarge to irregularly circular, slightly 
 sunken watersoaked blotches with gray centers. 
 
 This is a rather widespread disease of the vines, and pod 
 infection occurs in the field. It seems likely that the spots 
 enlarge during transit. Bacterial spot was found commonly 
 in the Chicago market in the summer of 1918, and appeared 
 to predispose the stock to secondary rots. 
 
 No control is known at present. 
 
 PEA: POD SPOT. 
 
 Cause: A fungus (Ascochyta pisi). 
 
 The symptoms of this disease are rather small, definitely 
 circular and sharply depressed spots with tan-colored or 
 pinkish centers often bearing small pimples, the pycnidia of 
 the fungus. 
 
 This is a serious field disease affecting the leaves and 
 stems as well as the pods. Pod infection occurs in the field, 
 and there is probably little spread of the disease during 
 transit. 
 
 Control involves crop rotation and the use of disease-free 
 seed. 
 
 Ref. (73). 
 
 PEA: SLIMY SOFT ROT; BACTERIAL ROT. 
 
 (See Slimy Soft Rot). 
 
 PEA: WATERY SOFT ROT; SCLEROTINIA ROT. 
 
 (See Watery Soft Rot). 
 
 PEPPER: ANTHRACNOSE. 
 
 Cause: A fungus (Gloeosporium). 
 
 Slate-colored to charry black, sunken lesions are char- 
 acteristic of this disease. The margins of the lesions either 
 are darker colored or watersoaked but of the same color as 
 the healthy tissue, and wrinkled. Under moist conditions 
 salmon-colored dots or spore heaps occur, which may run 
 together and form a slimy mass. These dots are the acer- 
 vuli (sing, acervulus) of the fungus and furnish a positive 
 diagnostic character for this disease. 
 
 This disease is found frequently on peppers. Very fre- 
 quently, under market conditions, the lesions do not bear 
 
MARKET DISEASES OF VEGETABLES. 43 
 
 cicervuli but become covered with a black, velvety growth of 
 Alternaria species. 
 
 PEPPER: RHIZOPUS ROT. 
 
 (See Rhizopus Rot). 
 
 PEPPER: SLIMY SOFT ROT; BACTERIAL ROT. 
 
 (See Slimy Sjft Rot). 
 
 PEPPER: WATERY SOFT ROT; SCLEROTINIA ROT. 
 
 (See Watery Soft Rot). 
 
 PEPPER: SUN-SCALD. 
 
 (See Sun-Scald). 
 
 POTATO: BLACK SCURF AND RUSSET SCAB. 
 
 . Cause: A fungus (Rhizoctonia). 
 
 Black scurf and russet scab are skin diseases. Affected 
 potatoes are rough and dirty in appearance, or may have a 
 cracked or corroded skin. Both are field diseases caused by 
 the same fungus. 
 
 Black scurf is characterized by the presence of small 
 brown or black masses or sclerotia on the tuber, often re- 
 ferred to as "dirt which will not rub off." These masses 
 may be circular or irregular in outline and single or joined 
 into series. Washing the tuber brings these into sharp relief. 
 
 Russet scab is a corrosion of the tuber skin. In some cases 
 smooth-skinned tubers show local or general netting, either 
 slight, or so extensive as to resemble the skin of netted varie- 
 ties. In advanced stages the corrosion becomes channeled, 
 and the intersecting channels may become so deep that the 
 tuber surface suggests alligator hide. 
 
 In many cases, tubers are literally covered with black 
 scurf without any apparent russeting, while in other cases 
 the presence of the fungus seems to cause only a cracking 
 or scabbing, without any sclerotia. 
 
 Generally neither black scurf nor russet scab are serious 
 enough to affect the market value of potatoes. The former 
 occasionally is severe enough to affect the appearance of the 
 tuber. At times, in very moist cars or storage places, the 
 sclerotia germinate, and the potatoes become covered with 
 a luxuriant growth of mold which detracts from the good 
 appearance of the lot. Russet scab, however, affects the 
 appearance of the tuber more markedly, and often corrodes 
 the skin suffciently to necessitate deep paring, which is 
 attended by a waste of food. 
 
 Ref. (50); (64). 
 
 POTATO: SILVER SCURF. 
 
 Cause: A fungus (Spondylocladium atrovirens). 
 
44 U. S. DEPARTMENT OF AGRICULTURE. 
 
 Silver scurf is a skin disease which is purely superficial, 
 and does not penetrate below the cork layer. The infected 
 areas are marked by their silvery appearance, which is espe- 
 cially pronounced if the tubers are washed. In late stages 
 of the disease, the affected skin becomes wrinkled and 
 sloughs off. 
 
 Generally, affected areas occur near the stem end, but 
 they may be found over the entire surface. Diseased areas 
 vary from one-fourth inch to one inch or more in diameter. 
 
 In storage, especially under moist conditions, a sooty layer 
 composed of the spores of the fungus may be found on the 
 diseased areas. 
 
 Infected stock is fit for table use. 
 
 Ref. (43); (57). 
 
 POTATO: WART. 
 
 Cause: A fungus (Chrysophlyctis endobiotica). 
 
 In its early stages, wart is characterized by small, warty 
 outgrowths which usually occur at the eyes of the tuber. 
 These warts later become very large, and in severe cases, 
 cover or involve the entire tuber. They are rough and black 
 in color. 
 
 This disease is serious in certain parts of Europe, and has 
 recently made its appearance in the United States (Penn- 
 sylvania). It is a very destructive field disease, and may be 
 carried with diseased seed tubers. Once having gained a 
 foothold, the fungus persists for long periods in the soil. 
 
 Infection takes place in the field while the tubers are 
 growing. The disease does not progress in storage, and does 
 not spread to healthy tubers. Diseased stock is very subject 
 to secondary rots, and in this way it is a menace to healthy 
 stock. Slightly affected tubers may be used for table 
 purposes. 
 
 Precaution against the use of diseased tubers for seed 
 purposes is of prime importance in the prevention of this 
 disease. With this end in view a National quarantine has 
 been established. 
 
 Ref. (35); (63). 
 
 POTATO: COMMON SCAB. 
 
 Cause: A fungus (Actinomyces scabies). 
 
 Scab is characterized by rough corky elevations, or by 
 pits. If tubers are attacked early, the pits are deep ; if late, 
 they may be shallow and superficial. In the early stages, 
 affected tubers are marked with minute, reddish or brown- 
 ish surface lesions. Cork formation usually occurs under- 
 neath these lesions. Often the lesions coalesce and in severe 
 cases the entire tuber may be covered by a rough incrusta- 
 tion. Scabby potatoes are little if any more disposed to 
 decay than clean potatoes. 
 
MARKET DISEASES OF VEGETABLES. 45 
 
 Deep scab is an advanced stage of common scab. Often 
 insects or mites live in scab pockets. It is not known to just 
 what extent these are responsible for the Lesions. 
 
 Common scab occurs in all varieties of potatoes and is 
 most common in potatoes grown in alkaline soil. Treatment 
 of seed stock with corrosive sublimate, and planting in unin- 
 fected soil or acid soil are fair preventives of the trouble. 
 
 Wire worm or grub injury often are confused with scab 
 lesions. It frequently is difficult to differentiate between 
 them. Wireworm injury is generally marked by extensive 
 channeling in the tuber skin, while grub injury is marked by 
 deep, broad pits with protruding or overhanging rims. Wire- 
 worm and grub injuries often are points of entry for Fusa- 
 rium species. 
 
 Scab and insect injuries depreciate the value of tubers 
 for table use by making them unsightly, and by necessitat- 
 ing deep paring with attendant loss of food. 
 
 Ref. (10); (38); (39); (50). 
 
 POTATO: POWDERY SCAB. 
 
 Cause: A slime mold (Spongospora subterranea). 
 
 In the early stages powdery scab consists of pimple or 
 blister-like eruptions, one-sixteenth to one-quarter inch in 
 diameter, which are completely covered by the skin of the 
 tuber. Later these coverings rupture and expose pits, which 
 are single or joined, and fringed by the flaring, papery, 
 torn, and more or less toothed remnants of the skin. The 
 interior of these pits is at first filled with a brown powder 
 or dust, which is usually absent when the tubers reach mar- 
 ket. Often the tissues surrounding the pits become discol- 
 ored and sunken, and each pit or group of pits appears as a 
 crater in a sunken zone. 
 
 Powdery scab differs from common scab in the more 
 nearly circular lesions, smaller pits, presence of brown dust, 
 star-like rupture of the skin, and relative absence of cork 
 formation. 
 
 This disease is not as serious a menace as it was once 
 thought to be. It seems to be localized in a few sections of 
 North America, and is causing little damage. It is favored 
 by cool, moist weather. 
 
 The causal organism is introduced into the soil with dis- 
 eased seed stock, and tuber infection occurs in the field. 
 
 Affected stock is fit for table use. Its market value, how- 
 ever, is decreased because of its unsightliness, and because 
 of the waste due to deep paring. 
 
 Ref. (44); (46). 
 
 POTATO: LATE BLIGHT TUBER ROT. 
 
 Cause: A fungus (Phytophthora infestans). 
 
 Late blight tuber rot is characterized externally by de- 
 pressed, discolored areas of irregular but definite outline. 
 These may occur merely as spots or as very extensive lesions. 
 
46 U. S. DEPARTMENT OF AGRICULTURE. 
 
 The affected areas often have a metallic or purplish tinge 
 which is especially marked at the margin where the dis- 
 eased tissue joins the healthy. At times, a pinkish color is 
 apparent when the outer skin of affected areas is first re- 
 moved. The diseased tissues underlying the sunken areas 
 are browned, and unless secondary rots have set in, are quite 
 dry and firm. The tissue is merely killed, not disintegrated. 
 In cross section it is seen that the affected tissue tends to be 
 limited to the outer parts of the tuber, and that the advanc- 
 ing edge is irregular and feathery. 
 
 Under storage conditions, especially if the air is very 
 moist, secondary rots due to bacteria or fungi set in. At 
 times, in advanced cases, it is difficult to ascertain whether 
 the primary cause of rotting was freezing injury, with sub- 
 sequent bacterial and fungous infection, or late blight. In 
 such cases the deciding factors are the presence in the ship- 
 ment of clear-cut cases of late blight or of freezing injury. 
 
 Potatoes affected with late blight do not show the hollow 
 brittle regions found in potatoes affected with Fusarium 
 tuber rot, nor the shriveled and wrinkled surfaces caused by 
 Fusarium or freezing injury. The feathery edge of the 
 tissue killed by the late blight fungus also serves to differ- 
 entiate it from tissues killed by Fusarium or freezing. 
 
 Late blight tuber rot occurs most commonly in potatoes 
 grown in the Eastern and North Central States, and in the 
 coastal portions of the Pacific Northwest States. Under cer- 
 tain weather conditions, it also occurs in southern potatoes. 
 During the rainy season of 1918, late blight was prevalent 
 in Florida potatoes. It is not a hot weather disease but is 
 favored by cool, wet weather. 
 
 Late blight is one of the most important field diseases of 
 the potato, causing a severe blight of the vines in addition 
 to its attack on the tubers. 
 
 The fungus overwinters in diseased tubers, and is intro- 
 duced into the field with diseased seed stock. From dis- 
 eased seedlings produced by such seed, the fungus spreads 
 rapidly throughout the field when weather conditions are 
 favorable. Tubers are infected in the field by spores washed 
 down or spattered from the diseased vines. The disease 
 also develops in transit and storage. 
 
 Late blight can be controlled in the field by spraying with 
 Bordeaux mixture. Its development in transit and storage 
 is checked by a dry atmosphere and a low temperature (34 
 to 36 F.; 45 F. is too warm). It is highly desirable that 
 diseased tubers be sorted out as soon as they can be de- 
 tected. In case of a late blight epidemic, digging should be 
 postponed until the tops have dried up. 
 
 Affected tubers are not marketable for table use. They 
 are also a menace to sound stock in transit and storage since 
 secondary rots, such as Fusarium or slimy soft rot, very fre- 
 quently follow late blight. 
 
 Ref. (9); (18); (34); (45). 
 
MARKET DISEASES OF VEGETABLES. 47 
 
 POTATO: FUSARIUM TUBER ROT. 
 
 Cause: Fungi (Fusarium species) . 
 
 Fusarium tuber rot is generally marked by sunken, shriv- 
 eled, wrinkled, or broken areas* on the tuber surface. These 
 areas may be brown to black in color and on them may 
 appear masses of whitish or brightly colored mold. 
 
 The diseased tissue underlying such discolored and 
 shrunken areas may be dry and brittle, and may contain 
 cavities lined with a white or bright colored growth of the 
 fungus responsible for the rot; or this tissue may be watery 
 but intact, depending upon the species of fungus responsible 
 for the rot and the conditions under which the affected tuber 
 was kept. Usually, if affected tubers are kept in a dry cool 
 place, the dry, brittle, and hollow type of powdery dry rot 
 results. If they are kept in a warm moist place the soft 
 intact type of rot is usually the result. Affected tissue may 
 be gray or brown to black in color. 
 
 The rot may proceed from the stem or seed end, from the 
 eyes or from broken places in the skin, such as cuts and 
 bruises. At times the infection is confined to a mere dis- 
 coloration of the vascular ring proceeding from the stem 
 end of the tuber. This is not visible until the tuber is cut. 
 This discoloration cannot always be positively differenti- 
 ated, without miscroscopic examination and cultural test, 
 from discolprations due to freezing injury or to varietal 
 characteristics. Fusarium discoloration penetrates much 
 farther into the tuber, however, than other vascular dis- 
 coloration. In southern potatoes, this discoloration in the 
 ring can be told from a similar discoloration due to brown 
 rot by the absence of the slimy bacterial masses or droplets 
 which ooze out when tubers affected with brown rot are cut. 
 
 This stem-end infection and some lenticel and eye infec- 
 tions occur in the field. Stem-end invasion is very common 
 in potatoes produced by plants affected with Fusarium wilt. 
 Jelly-end is another type of stem-end infection which occurs 
 in the field. However, most of the tubers rotted by Fusa- 
 rium species are infected through breaks in the skin caused 
 during and after the harvest. 
 
 Tubers with areas injured or killed by freezing are very 
 subject to Fusarium rots. The rot usually starts in at some 
 point which did not heal over completely with cork or was 
 not entirely sealed with starch following the drying out of 
 the frozen tissue. At times it is very difficult to distinguish 
 between potatoes with frozen areas which were subse- 
 quently infected with Fusarium tuber rot, and potatoes 
 which were originally affected with the rot and then kept 
 under moist conditions. The end result in both cases is 
 usually a wet brown rot. This wet type of rot is especially 
 marked in the Burbank and Netted Gem potatoes from 
 Idaho. It may be practically impossible at times to deter- 
 mine the cause of the decay by examination of a single tuber 
 
48 U. S. DEPARTMENT OF AGRICULTURE. 
 
 without a microscopic examination or cultural test. An 
 examination of the entire lot, however, will reveal the pres- 
 ence or absence of typical signs of freezing injury. The 
 frozen tissue of a tuber usually is set off from the healthy 
 tissue by a more or less straight purple or brown line which 
 extends across all the tissues of the tuber, or by a gray, 
 chalky, brittle layer of starch. On the other hand, most 
 Fusarium species generally tend to rot the center -of the 
 tuber faster than the cortical tissue, leaving a shell of sound 
 tissue enclosing a rotted center. 
 
 An examination of the surface of a tuber may not be suf- 
 ficient to determine whether the tuber is affected* with late 
 blight or Fusarium tuber rot. Both produce sunken dis- 
 colored areas. The late blight tuber rot, however, causes 
 more of a metallic luster than the Fusarium tuber rot, and 
 usually the sunken area is not shrunken and shriveled. In 
 tubers affected with late blight, the diseased tissues under- 
 lying the discolored areas are solid and dry and have a 
 feathery edge, while in the Fusarium tuber rot the diseased 
 tissue, if dry, contains cavities or is watery and soft and in 
 cross-section is set off from healthy tissue by a sharp, smooth 
 edge. 
 
 Tubers affected with the soft, wet, brown type of Fusa- 
 rium tuber rot can be differentiated from tubers affected 
 with the slimy soft rot by the absence of the foul odor so 
 characteristic of all bacterial soft rots. Fusarium-infected 
 tissue is not slimy even though it is soft and disintegrated. 
 
 Deterioration of tubers due to Fusarium tuber rot is some- 
 times rapid and often complete. Infected tubers are a men- 
 ace to healthy ones. Immature tubers, cut and bruised 
 tubers, tubers with second growth knobs which are easily 
 broken off, tubers affected with other diseases such as late 
 blight tuber rot or blackleg, and tubers with frozen areas 
 are an easy prey for the Fusarium species causing tuber rot. 
 
 One or more forms of Fusarium tuber rot occur in practi- 
 cally all potato districts. Fusarium tuber rot is much more 
 common in northern than in southern potatoes. It does 
 develop, however, in southern potatoes shipped north and 
 causes a very soft, watery rot or a stem-end rot. The orig- 
 inal infection may occur in the field, in transit or in storage, 
 but in most cases the rot develops and spreads in transit and 
 storage. In a few cases, such as jelly-end rot and black field 
 rot, the disease develops in the field. 
 
 The Fusarium tuber rot in potatoes from the Central 
 Western States, especially in the Early Ohio stock from 
 Nebraska and Minnesota, and the Burbank and Netted Gem 
 stock from Idaho, is called powdery dry rot. This term 
 refers more to the appearance of the spore masses of the 
 fungus than to the diseased tuber tissues. The Fusarium 
 tuber rot in potatoes from the Eastern States is designated 
 as tuber rot or dry rot and generally is of the wet type. The 
 
MARKET DISEASES OF VEGETABLES. 49 
 
 Fusarium tuber rot appearing at the end of the tuber in the 
 long, white varieties of the Northwest, such as the Burbank, 
 is known as jelly-end, while that appearing in other parts of 
 the tuber, especially marked in the round varieties such as 
 the Rural, is known as "black field rot." These rots are 
 caused by Fusarium radicicola, which also causes a very soft 
 leaky rot and a dry, black stem-end rot of potatoes grown 
 in the southern half of the Mississippi Valley. 
 
 Wounded or bruised surfaces which have become sealed 
 with starch or cork should not be confused with Fusarium 
 infections. Generally tuber rot starts in bruises and cuts. 
 During the early storage season, it is often impossible to 
 determine whether or not a bruise or cut will develop tuber 
 rot. Later in the season the presence of soft discolored 
 tissue or cavities lined with mycelium makes a diagnosis 
 much easier. 
 
 The safest and surest methods of control are careful han- 
 dling of tubers to avoid cutting and bruising; sorting out of 
 bruised, broken, cut, diseased, and frozen potatoes; and 
 storing of tubers in a well-ventilated place at a temperature 
 between 36 and 40 F. 
 
 Ref. (7); (37). 
 
 POTATO: JELLY END ROT; BLACK FIELD ROT. 
 
 Cause: A fungus (Fusarium radicicola). 
 
 Both jelly end and black field rot are types of the Fusa- 
 rium tuber rot previously described. In jelly end rot, the 
 end of the tuber is shrunken and collapsed, while black field 
 rot is characterized by shrunken, collapsed, black to brown 
 areas occurring anywhere on the surface of the tuber. 
 
 The diseased tissue underlying the discolored or shrunken 
 surface is soft, watery, and light to dark brown or black in 
 color, or it may be rather firm and black. Unlike powdery 
 dry rot, cavities generally do not occur in the affected 
 tissues. 
 
 The moist condition of jelly end rot is not observed unless 
 the potatoes have just been dug or have been removed re- 
 cently from a car which sweated or became overheated in 
 transit. Generally, under market conditions, the disinte- 
 grated tissue dries out and resembles typical dry rot. Very 
 often stock affected initially with jelly end or black field rot 
 subsequently becomes affected with powdery dry rot, which 
 progresses rapidly in storage. 
 
 These rots occur most commonly in Nebraska, Idaho, and 
 Pacific Coast potatoes. Jelly end rot is prevalent in the long 
 varieties such as the Burkbank type, while black field rot is 
 most clearly marked in the round varieties such as the 
 Rural. Without a cultural examination it is impossible to 
 differentiate at times between jelly end rot and so-called 
 dry rot of the end of the tuber caused by Fusarium species 
 other than Fusarium radicicola. 
 
50 U. S. DEPARTMENT OF AGRICULTURE. 
 
 The original infection takes place in the field. Both dis- 
 eases develop in the field. They probably do not develop or 
 spread in transit and storage, but do open the way for other 
 Fusarium tuber rots. 
 
 Fusarium radicicola may cause in southern potatoes a very 
 watery leaky rot which involves the entire tuber and re- 
 sembles the watery soft rot of other vegetables caused by 
 Sclerotinia. This rot differs from jelly end and black rot 
 in that the whole tuber is affected and that the rot is watery 
 rather than jelly-like or firm. The diseased tissue is only 
 slightly discolored. Under certain conditions in transit, an 
 extensive mycelial growth and numerous bodies which re- 
 semble small sclerotia develop on the surfaces of affected 
 tubers. 
 
 In this leaky rot of southern-grown potatoes caused by 
 Fusarium radicicola, the original infection takes place in the 
 field. This type of rot is favored by hot weather, and is very 
 frequently associated with scald. It is probable that this 
 disease, unlike jelly end or black field rot, develops and 
 spreads rapidly in transit. 
 
 Ref. (7); (54). 
 
 POTATO: POWDERY DRY ROT. 
 
 Cause : A fungus (Fusarium trichothecioides) . 
 
 Powdery dry rot is a type of the Fusarium tuber rot pre- 
 viously discussed. In the name powdery dry rot, the word 
 powdery does not refer to the appearance of the diseased 
 tissue but to the powdery masses of spores formed by this, 
 fungus. 
 
 In this disease the affected region contains cavities sepa- 
 rated by dried brownish tissue and starch and lined with 
 whitish fluffy mycelium or powdery pink masses of spores. 
 In the early stages, the affected tissue is light brown to black 
 in color and is sharply delimited from the healthy tissue by 
 a layer of brown or black tissue. Affected tubers are much 
 lighter in weight than healthy tubers because of the exten- 
 sive hollow areas. This rot is most pronounced in the cen- 
 tral portion of the tuber, and as a result, affected tubers 
 often become more or less hollow shells. 
 
 If tubers infected with powdery dry rot are stored in a 
 very moist atmosphere, or if they become infected with bac- 
 teria, the typical symptoms are partly masked by the pres- 
 ence of soft watery tissues of chocolate color, which gener- 
 ally are more extensive than the typical dry areas. 
 
 Potatoes just taken from a car which has been in transit a 
 long time, or which was not cooled or ventilated properly, 
 show the symptoms of wet Fusarium rot rather than the 
 symptoms of powdery dry rot. However, upon exposure to 
 the air the typical dry rot symptoms soon develop. 
 
 Powdery dry rot appears to progress more rapidly at 
 lower temperatures than the other Fusarium tuber rots. It 
 occurs mainly in Idaho and other Rocky Mountain districts, 
 
MARKET DISEASES OF VEGETABLES. 51 
 
 and in western Nebraska, being especially severe in the 
 Early Ohio variety. It is prevalent in bruised or frozen 
 potatoes from Washington, Idaho, Nebraska and Colorado. 
 
 Infection takes place through breaks in the skin of the 
 tuber. These may be brought about by cuts or bruises, by 
 freezing and by attacks of other fungi. The spores of Fusa- 
 rium are usually everywhere present in the soil, on the sur- 
 faces of tubers, and in storage places, so that any break in 
 the tuber skin is very likely to become infected. 
 
 Control of this disease depends upon careful handling of 
 potatoes to minimize injury as far as possible. Because of 
 the rapid progress of the rot, it is advisable to dispose of 
 affected stock at the earliest opportunity. It is not profit- 
 able to ship severely affected stock. 
 
 Ref. (37) ; (53). 
 
 POTATO: LEAK. 
 
 Cause: Fungi (Pythium debaryanum; sometimes Rhiz- 
 opus nigricans). 
 
 Leak is marked at first by a brown discoloration around 
 wounds or bruised areas. The discoloration later becomes 
 extensive, and the entire interior of the potato may become 
 soft, and buff or light brown in color. Under pressure, the 
 affected tubers exude a brownish watery liquid, and dis- 
 eased tubers often leak badly. Potatoes affected with leak 
 are much more watery than those affected with the wet type 
 of Fusarium tuber rot. 
 
 Leak has been reported only from the Delta lands of the 
 San Joaquin Valley of California and from Idaho. It does 
 not occur in cool weather, and is entirely checked by heavy 
 frosts. 
 
 Infection takes place in the field, and tubers are infected 
 only through wounds, such as those due to fork injury or 
 the breaking off of second-growth knobs. Infection occurs 
 only in hot weather, but once the disease has gained a foot- 
 hold, it may devevlop at lower temperatures. 
 
 Leak can be controlled by careful digging and handling 
 of the potatoes and sorting out of bruised and broken tubers. 
 In addition it has been found advisable to hold suspected 
 potatoes 4 days in the warehouse before shipment so that 
 the disease, if present, may develop and be more readily 
 detected. It is not likely to be a storage trouble after the 
 warm season. 
 
 Ref. (28); (29). 
 
 POTATO: BROWN ROT (SOUTHERN BACTERIAL WILT). 
 
 Cause: Bacteria (Bacillus solanacearum). 
 
 Brown rot may be indicated externally by a slight depres- 
 sion at the point of attachment of the stolon to the tuber, or 
 by gray discolored patches on the surface. Sometimes no 
 external symptoms may be visible. Upon cutting infected 
 tubers, a moist brown discoloration and slight softening of 
 
52 U. S. DEPARTMENT OF AGRICULTURE. 
 
 the ring (vascular) tissue of the tuber is seen. White sticky 
 globules of bacteria ooze out from the cut tissues. In this 
 stage, the rot is odorless. 
 
 The rot begins in the vascular ring, causing cavities which 
 are filled with a dirty white, slimy, bacterial mass. Brown 
 rot may be followed by slimy soft rot to which the foul odor 
 of affected tubers is due. 
 
 This rot should not be confused with the ring discolora- 
 tion associated with Fusarium wilt. The latter is most 
 common in northern potatoes, while brown rot occurs only 
 in southern, especially Florida, stock. There is no bacterial 
 exudate from the bundles when a Fusarium infected tuber 
 is cut. 
 
 Infection takes place in the field and the disease is there 
 known as bacterial wilt. The infection proceeds from the 
 affected plant through the horizontal underground stems 
 (stolons) into the tubers which are enlargements of the 
 stolons. Potatoes grown in new soil are most severely 
 affected. 
 
 It is advisable not to plant potatoes in new ground. In- 
 fected stock is subject to decay and should be rapidly dis- 
 posed of. 
 
 Ref. (61). 
 
 POTATO: SLIMY SOFT ROT. 
 
 Cause: Bacteria (Bacillus carotovorus group). 
 
 This disease of the potato belongs to the class of slimy 
 soft rots described elsewhere, but, since it presents itself as 
 a special phase in southern potatoes, a separate discussion 
 is warranted. It is a soft, soupy, exceedingly foul smelling 
 rot. Unless affected tissue is discolored by other causes, 
 there is little change in color, the disintegrated tissue being 
 whitish to yellow. The boundary between the soft disinte- 
 grated and the firm sound tissue is very sharp. As the more 
 or less watery tissue dries, it becomes slimy and finally, 
 when completely dry, a mere chalky white crust. During 
 shipment the skin of affected areas is broken easily, and the 
 slime commonly is smeared over neighboring sound tubers. 
 In car-lot shipments this very materially increases the diffi- 
 culty of sorting. 
 
 Slimy soft rot very generally invades killed tissue. In a 
 wet soil, tubers often become asphyxiated, and the bacteria 
 enter the tuber through scab wounds, through lenticels (the 
 breathing pores of the tuber) , through broken places in the 
 skin, or through diseased stolons. Infection also occurs very 
 generally through bruises received during digging and han- 
 dling. If infected tubers are dug while wet, and scalded by 
 exposure to the hot sun, or if sacked with the wet soil adher- 
 ing, a procedure which may lead to heating or sweating, the 
 rot may progress rapidly from the surface inward through 
 the whole tuber. 
 
MARKET DISEASES OF VEGETABLES. 53 
 
 Brown rot may be followed by slimy soft rot as a result 
 of which large cavities are formed in the interior of the 
 tuber. The decayed tissue often is so viscous that it can be 
 pulled like very soft taffy. 
 
 Slimy soft rot is prevalent as a surface rot in potatoes 
 shipped from Florida, Louisiana and Texas. It is favored 
 by wet, hot conditions in the field, in transit or in storage. 
 After the rot has once started, the temperature is of less 
 importance than the humidity. This rot occurs also in 
 northern potatoes. Tubers affected with black-leg or with 
 scald or freezing injury are predisposed to slimy soft rot. 
 In fact, slimy soft rot commonly follows freezing injury if 
 the temperature after thawing is high enough to permit the 
 growth of the bacteria. 
 
 The control measures are careful sorting of stock which 
 has been subjected to unfavorable conditions before it is put 
 into transit or storage, and improvement of handling meth- 
 ods to avoid wounds and scald. The rot progresses and 
 spreads very rapidly in transit and storage, but can be 
 checked by rapid drying of affected stock. 
 
 POTATO: SURFACE MOLD. 
 
 Cause : Various fungi. 
 
 Under transit or storage conditions, potatoes often show 
 a superficial development of mold growth which is abso- 
 lutely non-injurious to the tubers except as it affects their 
 appearance. Various fungi are concerned, including blue 
 mold and Rhizoctonia, and their growth is favored by the 
 presence of moisture, especially the juice from nearby 
 frozen or rotted tubers. Wet, dirty tubers and cut or bruised 
 areas are likely to become covered with surface molds. 
 
 Surface molds are objectionable in bulk shipments be- 
 cause of the bad appearance of the stock. 
 
 Proper ventilation to dry the surfaces of the potatoes will 
 aid in preventing this trouble. 
 
 POTATO: HOLLOW HEART. 
 
 Cause : Rapid growth. 
 
 Hollow heart is a more or less irregular cavity in the 
 center of the tuber, varying in size and often lined by tissue 
 which is browned and glassy. 
 
 Hollow heart occurs most frequently in large, coarse, 
 rapid-growing varieties, particularly when these are grown 
 in very fertile soils. It also is common in red varieties grown 
 in the sand hills region of Nebraska. 
 
 Hollow heart and black heart may be confused since 
 cavities occasionally develop in tubers affected with black 
 heart ; but these differ from those of hollow heart by their 
 association with discolored tissue. 
 
 Usually hollow heart cannot be detected until the affected 
 potatoes are cut. It does not affect their keeping quality. 
 
 Affected stock is very undesirable for table use. 
 
 Ref. (49). 
 
54 U. S. DEPARTMENT OF AGRICULTURE. 
 
 POTATO: GROWTH CRACKS; SECOND GROWTH. 
 
 Cause : Unfavorable growing conditions. 
 
 Second growth and misshapen tubers are marked by a 
 development of knobs on the tuber's surface, and growth 
 cracks by wide, deep fissures, which are usually covered 
 with the normal protective cork layer of the tuber. 
 
 These malformations occur in all varieties and in all local- 
 ities, but are most pronounced where there is considerable 
 fluctuation in the water supply of the growing crop. 
 
 Second growth tissues are immature, and are subject to 
 peeling, bruising, and freezing injury. These knobs are 
 often broken off, opening a way for Fusarium infection. 
 
 Growth cracks ordinarily are not subject to tuber rot in- 
 fection, whereas mechanical injury such as cuts, splits, and 
 bruises, which are due to careless handling, do not develop 
 the normal layer of cork, hence become infected very 
 readily. 
 
 Tubers showing these deformities are of inferior grade, 
 since a considerable waste in paring is necessitated. 
 
 POTATO: IMMATURITY. 
 
 Cause : Premature death of vines in the field, or prema- 
 ture digging of the crop. 
 
 Immaturity is characterized by excessive peeling of the 
 skin, by a greenish tint under the skin, and by a tendency 
 to excessive wilting and flabbiness during transit and 
 storage. 
 
 This trouble occurs mainly in late varieties of the North 
 and in southern potatoes dug for early marketing. 
 
 Immature tubers are subject to bruising, therefore to 
 Fusarium tuber rot infection, to freezing injury, and to 
 excessive shrinkage if they are shipped in overheated cars. 
 They are not high grade stock and often are bitter in taste. 
 
 POTATO: NET NECROSIS AND INTERNAL BROWN SPOT. 
 
 Cause: Unfavorable field conditions (possibly mosaic 
 disease). 
 
 Net necrosis is characterized by fine, extensive brown 
 streaks which follow the vascular tissues and form a net- 
 work. The discoloration begins at the stem end, where it is 
 often localized ; or, in later stages, it may extend throughout 
 the whole tuber. The discolored tissues are dead. 
 
 It occurs in many varieties, and is favored by poor soil 
 conditions and by hot weather. 
 
 Internal brown spot is marked by brown or yellow re- 
 gions of dead tissues scattered throughout the tuber. The 
 affected regions may be small or large, even one-half inch 
 in diameter. They may be scarce or numerous, and are 
 isolated and not connected as in net necrosis. 
 
 The disease occurs in all varieties, and is favored by an 
 inadequate water supply during the growing period. 
 
MARKET DISEASES OF VEGETABLES. 55 
 
 Neither net necrosis nor internal brown spot should be 
 confused with freezing injury, which sometimes produces 
 very similar symptoms, but usually is otherwise distin- 
 guishable. 
 
 These internal discolorations are not decay and do not 
 impair the food value of the tuber, but affected portions 
 usually are rejected in the preparation of potatoes for the 
 table. 
 
 Ref. (49); (50). 
 
 POTATO: FREEZING INJURY. 
 
 Cause : Exposure to low temperatures in the soil or dur- 
 ing harvest, transit, or storage. 
 
 The symptoms of freezing injury are varied and complex 
 and may be general, appearing in all the tissues of a tuber, 
 or local and restricted to sharply limited regions of the 
 tuber. They depend upon the variety, maturity, and indi- 
 viduality of the potato affected, upon the varying predispo- 
 sition of the several tissues of the tuber to freezing injury, 
 upon the temperature to which the tuber was exposed, and 
 upon the rate of fall of the temperature as well as the dura- 
 tion of the exposure. The symptoms also depend upon the 
 interval between the time of injury and examination of the 
 affected tuber, and may or may not depend upon the rate of 
 thawing and the conditions under which this takes place. 
 
 Thoroughly frozen potato tissue no longer possesses the 
 natural crispness or brittleness of the sound potato. Frozen 
 tissue looks dull and does not cut readily nor with snap. 
 This is due to the formation of ice in the tissues. In the 
 freezing process, the cell water passes out of the cells into 
 the intercellular spaces, the spaces between the cells, where 
 it forms ice crystals. The extent to which the cell water 
 leaves the cells depends upon the point to which the tem- 
 perature is lowered, upon the rate at which this takes place, 
 upon the duration of the exposure, and upon the nature of 
 the potato. 
 
 The symptoms presented by thawed potato tissues are 
 very perplexing. Sometimes in case of severe freezing, the 
 tissues become turgid, blister-like, and swollen, and the skin 
 may be discolored. At other times they are quite firm and 
 remain intact and, contrasted with healthy tissue, merely 
 appear dull and colorless. If only a portion of a tuber was 
 severely frozen, usually a purplish band marks the border 
 of the uninjured tissue. When such a tuber is cut, the 
 border between healthy and injured tissue generally is 
 marked by a sharp purplish to dark brown line. However, 
 this line is not always present. 
 
 If no infection sets in, the more or less watery thawed 
 tissue dries down to the consistency of a rather moist mealy 
 mass or a shrunken, dull, grayish, very tough and leathery 
 granular mass which is composed of shrunken cells and 
 starch. Very frequently bluish to black colors develop. In 
 
56 U. S. DEPARTMENT OF AGRICULTURE. 
 
 this stage the dried-out starchy remnants of the tissue are 
 separated from the uninjured tissue by a dark brown corky 
 layer. 
 
 Very frequently the starchy or corky layer is not formed 
 before infection with Fusarium takes place, or it is subse- 
 quently broken and admits the fungus. Severe freezing 
 injury generally affects all tissues straight across the tuber, 
 while Fusarium rot develops most rapidly in the pith of the 
 tuber, leaving a shell of cortical tissue. This characteristic 
 sometimes is of service in differentiating freezing injury and 
 Fusarium tuber rot. 
 
 Thawed tissue, especially when in a warm damp atmos- 
 phere, is predisposed to slimy soft rot. In fact, most se- 
 verely frozen potato tissue is dead and sooner or later 
 becomes infected with the bacteria which cause this rot. 
 The bacteria get into the watery tissue, which is an excellent 
 growing medium for them, through breaks in the skin, and 
 cause a slimy, mushy, or soupy rot which has a very offen- 
 sive odor. Frequently the much wrinkled skin of such tubers 
 bursts, and the neighboring potatoes are smeared with the 
 slimy disintegrated tissue which dries out grayish and 
 chalky when exposed to the air. 
 
 It is very difficult at times to differentiate freezing injury 
 from injury due to scalding. This is especially true when 
 the first or last freezes of the season occur. 
 
 The severe general type of freezing injury is marked by 
 a killing of all the cells of the potato. The less severe type, 
 popularly known as chilling, is definitely localized and 
 restricted to the most susceptible tissues. It is known as 
 freezing necrosis. It appears first in the stem end, and at 
 times only the conducting tissues are killed and appear yel- 
 lowish-brown to black. Very often the conducting tissues 
 in the pith also are killed and appear as a net resembling 
 net necrosis. The storage tissues also may be affected, either 
 in extensive regions, or in small pockets. Starchy tissues so 
 affected are grayish to steel blue, even black in color, gran- 
 ular, and very tough and leathery. 
 
 Sometimes the thawing tissues are pinkish to red in color 
 when freshly cut. These colors change quite rapidly in the 
 air, becoming gray, brown, or dirty red. These colors should 
 not be confused with the pinkish color of the vascular ring 
 or pith tissue of some of the red varieties of potatoes. At 
 times white potatoes which have not been exposed to low 
 temperatures also have a pink color. Potato tissues when 
 freshly bruised and exposed to the air often are reddish in 
 color. 
 
 Potatoes subjected to freezing temperatures may show 4 
 none of the symptoms enumerated above but only a tend- 
 ency to excessive wilting and flabbiness. The cut tissue may 
 appear glassy and abnormally moist. When cooked they 
 may turn black in spots or may have a sweet taste. This 
 
MARKET DISEASES OF VEGETABLES. 57 
 
 condition also is frequently referred to as chilling injury. 
 When potatoes that have become sweet following exposure 
 to low temperatures are kept at normal temperatures the 
 sweet taste disappears. This, is due to the fact that the 
 increased respiration due to rise in temperature oxidizes the 
 excess of sugars which accumulated at temperatures of 29 
 to 34 F. At these tempertures the rate of respiration is cut 
 down more than the rate of digestion of starch into sugar 
 and consequently the sugars accumulate. 
 
 It is very difficult at times to differentiate immature 
 tubers from those showing the less severe types of freezing 
 injury. In both cases the tissues may have a greenish yellow 
 color, and may be flabby and bitter in taste. Immature 
 tubers are also bruised easily by impact or pressure, which 
 causes regions in the tuber to resemble chilled tissue so 
 closely that a diagnosis is excedingly difficult. It also is 
 exceedingly difficult to differentiate between thawed, dried- 
 out tissues and bruised tissues. 
 
 It seems in fact that the presence of ice in the tissues is 
 the only positive proof of freezing injury. All other char- 
 acteristics enumerated as symptoms of freezing and chilling 
 injury can also be brought about by other causes. 
 
 Slightly affected stock without extensive, discolored, 
 killed regions is suitable for food even though it is not as 
 palatable as the uninjured. It shrinks excessively in transit 
 and storage. 
 
 Guarding against the exposure of potatoes to tempera- 
 tures under 32 F. will prevent this type of injury. Losses 
 during transit may be avoided by careful sorting to elimi- 
 nate field frozen tubers previous to shipment, and the use 
 of all proper precautions to prevent freezing injury during 
 hauling, loading, and rail shipment. This involves proper 
 lining and preheating of the car, installation of false floor- 
 ing and ends, and an adequate heating apparatus regulated 
 during transit so as to avoid both freezing and black heart 
 injury. 
 
 Ref. (33a). 
 
 POTATO: BLACK HEART. 
 
 Cause : High temperature or insuffcient aeration. 
 
 The symptoms of black heart vary, depending upon 
 whether the potatoes are exposed to high temperatures with 
 an adequate air supply, or to high or normal temperatures 
 with an insufficient air supply. In the former case, no ex- 
 ternal symptoms develop ; in the latter, both external and 
 internal symptoms appear. 
 
 The external symptoms of black heart are moist areas on 
 the surface which may be purplish at first but turn brown 
 and black in a short time. The internal symptoms are a 
 dark gray to purplish discoloration which later becomes 
 jet-black. The discolored areas are usually sharply set off 
 from the healthy tissue. 
 
58 U. S. DEPARTMENT OF AGRICULTURE. 
 
 Generally the discoloration is restricted to the heart of 
 the tuber, but frequently it radiates to the exterior as well. 
 It may also appear on one side of a potato if this was ex- 
 posed to a stove in a railroad car or in the storage house. 
 The discolored regions may appear in zones in the periph- 
 eral parts and may be absent or less evident in the center. 
 In advanced stages, the affected tissue dries out and forms 
 cavities. In case cavities develop, these may be differenti- 
 ated from true hollow heart by their black lining of killed 
 tissue. 
 
 Exposure of potatoes in the field or in storage or transit 
 for a day to temperatures of 90 to 104 F. causes this 
 injury. Potatoes lying in a very hot soil or lying on the soil 
 after digging may show it. More generally the injury is 
 caused in stove-heated cars or by storing potatoes at 45 to 
 50 F. in piles deeper than 6 feet. In stove-heated cars, the 
 injury usually is most severe near the stove and at the top 
 of the load. 
 
 Black heart injury predisposes affected tissues to slimy 
 soft rot. The heated, killed and watery tissues offer excel- 
 lent growing conditions for bacteria. 
 
 Black heart does not impair the food value of non-affected 
 tissues. 
 
 Prevention of this injury in cars involves proper ventila- 
 tion, protection of the load near the stove with tin sheeting, 
 and careful attention to the fire. The temperature should 
 never go over 60 or 70 F. 
 
 The injury can be prevented in storage places by provid- 
 ing proper ventilation and by storing tubers in piles not 
 deeper than 6 feet. 
 
 Ref. (1); (68). 
 
 POTATO: SCALD. 
 
 Cause : Exposure to the hot sun. 
 
 Scald on potatoes may appear first as large blisters which 
 soon become sharply depressed or as slightly bleached areas 
 with a very irregular and lobed margin of a darker metallic 
 color. Upon cutting such a tuber, it is found that a shallow 
 surface layer of tissue has been killed. This killed tissue is 
 dull gray in color, and is separated from the uninjured tissue 
 by a brown and very irregular line. The killed tissue, if not 
 infected, dries out and becomes tough and leathery. 
 
 In many cases, more of the tuber is involved, both in sur- 
 face area and depth of the killed tissue. This type has been 
 tentatively named "deep scald," and shows much more dis- 
 coloration than the ordinary scald. Bluish black patches 
 often surround the lenticels, and the killed tissue darkens 
 very rapidly when cut surfaces are exposed to the air. 
 
 Scald differs from late blight tuber rot in that the affected 
 tissue is not brown in color, and in the sharp line of demarca- 
 tion between the dead and the living tissue. Scald differs 
 from freezing injury in its much more irregular surface out- 
 
MARKET DISEASES OF VEGETABLES. 59 
 
 line and in the more irregular plane of separation between 
 killed and sound tissue. At certain seasons, it may be very 
 difficult to make this differentiation positive without rather 
 careful inspection of car lots. Freezing injury, however, 
 should be accompanied by other unmistakable symptoms. 
 
 Scald of potato is probably caused by exposure of newly 
 dug tubers to the hot sun in the field. 
 
 Scald is of the highest importance from the market point 
 of view. The killed tissue is very subject to the attacks of 
 rot-producing organisms such as Fusarium and especially 
 the bacteria of slimy soft rot. In the Chicago market in the 
 summer of 1918, there were enormous losses due to slimy 
 soft rot following scald in shipments of potatoes from the 
 South and the entire Mississippi Valley. 
 
 It is not advisable to ship potatoes showing scald because 
 of their extreme predisposition to slimy soft rot during 
 transit. 
 
 POTATO: SALT INJURY. 
 
 Cause : Contact of potatoes with the floor or walls of a 
 car in which fertilizers, salt, or salted hides have been 
 shipped. 
 
 Usually the side of the potato in contact with the floor or 
 wall is flattened, and the injured tissue is soft and flabby 
 and at times semi-watery. At times the injured tissue is firm 
 and leathery. Before the air has free access to the tissue it 
 usually is colorless. After a short exposure to the air if not 
 infected the injured tissues become brown to black, and 
 begin to dry out. The exterior of the injured region gener- 
 ally is black. Frequently the injured tissue has a distinct 
 salty taste, and salt injury may be thus diagnosed. 
 
 Tubers affected with salt injury are predisposed to slimy 
 soft rot, and generally become infected and soupy if not 
 removed promptly from the car. 
 
 POTATO: SUNBURN. 
 
 Cause : Exposure of tubers to light, either in the field, or 
 during harvest, shipment and storage. 
 
 Sunburn is marked by a green discoloration of the surface 
 layers, and in severe cases, of the interior portions of the 
 tuber. 
 
 Sunburn occurs in potatoes of all varieties upon prolonged 
 exposure to the light. It is common in eastern stock shipped 
 in midsummer. 
 
 Affected stock is bitter and unfit for food. 
 
 POTATO: BRUISES, CUTS, AND SPLITS. 
 
 Cause: Mechanical injury. 
 
 Bruises may be superficial or internal. The most common 
 type of bruise occurs in immature potatoes whose tissues 
 are very tender and crisp, and consequently are easily 
 broken either by pressure or by friction. Often an immature 
 
60 U. S. DEPARTMENT OF AGRICULTURE. 
 
 tuber is gouged by rubbing against the container or by being 
 walked upon. In either case, the result is a loss of water 
 by the injured cells, leaving a solid, grayish, starchy deposit. 
 At times this deposit is black, and externally the bruised 
 areas often appear black. These types of bruising are very 
 common in potatoes grown under irrigation. The injury 
 due to gouging is more severe than peeling or feathering 
 though it usually is due to the same causes. 
 
 Often potatoes are bruised or crushed by impact or by 
 the weight of the load. In addition to the injuries above 
 described, impact or pressure may cause symptoms which 
 may be wholly internal or may be indicated externally only 
 by small, slightly sunken spots. At times these internal in- 
 juries resemble those due to freezing and consist of small 
 pockets of grayish, starchy masses, the remnants of rup- 
 tured, dried-out cells. 
 
 Most of the cuts in potatoes are caused by digging imple- 
 ments, and by the pernicious custom of handling potatoes 
 with steel shovels or forks. Cuts may be broad and shallow 
 or very deep. 
 
 If the cut or bruised tissue has an opportunity to dry out 
 rapidly the injury may be sealed by a grayish granular 
 deposit of starch, and later by a brown layer of cork. Very 
 often, however, especially under moist conditions, Fusarium 
 gets a foothold before the bruised or cut tissue is healed. It 
 may also enter through subsequent breaks in the dry starch 
 layer. In very hot weather, especially in southern potatoes, 
 slimy soft rot gets a start in bruises and cuts. Shallow, 
 broad, or smooth cuts are less subject to infection than those 
 which are deep and ragged. 
 
 Potatoes often are fractured by pressure or by impact. 
 Careless throwing about of potatoes, heavy loading, walking 
 upon potatoes, and similar rough treatment, are responsible 
 for these fractures or so-called splits. These may be visible 
 externally or they may be wholly internal. In either case 
 the surfaces of the fracture are lined with a deposit of starch 
 or a brown layer of corky tissue. At times freshly dug 
 potatoes develop splits if they dry out too rapidly. 
 
 Bruised, cut, or split potatoes are suitable for food, though 
 the injuries necessitate very appreciable losses in paring. 
 Their presence, however, lowers the market value of a 
 shipment. 
 
 These mechanical injuries generally are ports of entry for 
 fungi and bacteria which cause tuber rots. In most cases of 
 Fusarium tuber rot, the infection starts in such injuries. In 
 the early part of the shipping or storage period, it is impos- 
 sible without a cultural test to determine whether a me- 
 chanical injury will remain merely an injury or develop a 
 tuber rot. However, as the season progresses, the rot symp- 
 toms become more pronounced. 
 
 This type of injury with its frequently disastrous conse- 
 quences could be prevented if it were constantly borne in 
 
MARKET DISEASES OF VEGETABLES. 61 
 
 mind that potatoes consist of living cells and should not be 
 handled like stones. 
 
 POTATO: ENLARGED LENTICELS. 
 
 Cause : Excessive water supply during the growing season. 
 
 This is marked by flat, pimple-like swellings, which occur 
 at the lenticels of tubers. These swellings are formed by 
 proliferation of cells lining the cavity of lenticels. Normally 
 these cells remain dormant but they may enlarge and divide 
 if potatoes are grown in very wet soil or if the soil becomes 
 waterlogged after the tubers are formed. If this process 
 continues long enough a mass of cells protruding above the 
 tuber surface is formed. 
 
 At first these cells are quite soft, whitish in color, and 
 quite easily rubbed off. Later they harden and become 
 brown and corky. 
 
 Potatoes showing enlarged lenticels are objectionable 
 because of bad appearance of the stock. Their food value 
 is not impaired, since the swellings are superficial. 
 
 POTATO: FLEA-BEETLE DISEASE. 
 
 Cause: The larva of the flea beetle (Epitrix cucumeris 
 Harr.). 
 
 In the simplest cases flea-beetle injury is marked by corky 
 pimples or raised places on the tuber. At times the surface 
 of such pimples is slightly broken. In the more Complex 
 and advanced stages the surface of the tuber is a mass of 
 pimples and of channels or furrows formed by breaking of 
 the skin. The margins of such furrows and channels fre- 
 quently are elevated and swollen so that the whole furrow 
 stands above the surface of the tuber. This type of injury 
 frequently is known as worm tracks. 
 
 By cutting into the pimples or furrows brown, tough 
 splinters of corky tissue are found extending perpendicu- 
 larly into the tuber tissue. Sometimes these splinters are a 
 fourth of an inch in length. Their presence serves to differ- 
 entiate the simple, pimple stage of flea-beetle injury from 
 slight nematode injury, and the furrowed type from other 
 tuber diseases such as scab, grub injury, or wire-worm 
 injury. 
 
 Flea-beetle injury is most frequent in Colorado potatoes. 
 It injures the appearance of potatoes and generally -necessi- 
 tates very deep paring. 
 
 POTATO: NEMATODE DISEASE. 
 
 (See Nematode Disease). 
 
 RADISH: BLACK ROOT. 
 
 Cause: A fungus (Rheosporangium aphanidermatum). 
 
 This disease of radish roots is characterized by blackened 
 regions of varying size which may be rather superficial, or 
 may extend deeply into the root. The darkened tissue is 
 
62 U. S. DEPARTMENT OF AGRICULTURE. 
 
 firm and not disintegrated. The lesions are often cracked 
 or fissured on the surface as a result of root growth, and 
 may be accompanied by some disfiguration of the root due 
 to checked growth. 
 
 This disease is of widespread occurrence. Both red and 
 white varieties are susceptible. The fungus persists in the 
 soil and often causes damping-off of seedlings. 
 
 Badly affected roots often are found in the market, but 
 are not considered edible, and their presence lowers the 
 value of the bunch. 
 
 Control involves crop rotation or soil sterilization. Badly 
 affected roots should not be sent to market. 
 
 Ref. (16). 
 
 RADISH: MISCELLANEOUS DISEASES. 
 
 DOWNY MILDEW. 
 
 Cause: A fungus (Peronospora parasitica). 
 
 Downy mildew causes angular spots on the leaves, 
 bounded by the larger veins. These spots are yellow in color 
 when viewed from above, and the under surface is covered 
 with a white felt-like outgrowth of mold. 
 
 This disease often is found in the market but is of no 
 importance since the root is not attacked. 
 
 WHITE RUST. 
 
 Cause: A fungus (Cystopus candidus). 
 
 The symptoms of this disease on the leaves are small, 
 irregular lesions bearing on the under surface smooth, pure 
 white, porcelain-like cushions or blisters. These rupture, 
 allowing the spores to escape, and the lesions are then 
 recognizable by the torn edge of the empty pustule. Often 
 these lesions cause marked distortion in the leaves and other 
 affected parts. 
 
 Since this disease does not occur on the roots, it is of no 
 importance in the market. 
 
 ROOT ROT. 
 
 Cause: A fungus (Rhizoctonia). 
 
 This disease is marked by a rather large brown circular 
 lesion on the side of the root in which the tissue is rotted 
 as in watery soft rot. 
 
 This has been found occasionally in the market. 
 
 NEMATODE DISEASE. 
 
 (See Nematode Disease). 
 
 RADISH; SLIMY SOFT ROT; BACTERIAL ROT. 
 
 (See Slimy Soft Rot). 
 
 RUTABAGA: DRY ROT. 
 
 (See Radish Root Rot). 
 
MARKET DISEASES OF VEGETABLES. 63 
 
 RUTABAGA: GRAY MOLD ROT; BOTRYTIS ROT. 
 
 (See Gray Mold Rot) . 
 
 RUTABAGA: SLIMY SOFT ROT; BACTERIAL ROT. 
 
 (See Slimy Soft Rot). 
 
 RUTABAGA: WATERY SOFT ROT; SCLEROTINIA ROT. 
 
 (See Watery Soft Rot). 
 
 RUTABAGA: NEMATODE DISEASE. 
 
 (See Nematode Disease). 
 
 SALSIFY: WATERY SOFT ROT; SCLEROTINIA ROT. 
 
 (See Watery Soft Rot and Beet Watery Soft Rot). 
 
 SPINACH: SLIMY SOFT ROT; BACTERIAL ROT. 
 
 (See Slimy Soft Rot). 
 
 SQUASH: RHIZOPUS ROT. 
 
 (See Rhizopus Rot). 
 
 SWEET POTATO: BLACK ROT. 
 
 Cause: A fungus (Sphaeronema fimbriatum). 
 
 Black rot is characterized by greenish to nearly black, 
 circular, depressed spots, varying in size from y% to 2 inches 
 in diameter. At times the spots are very irregular, occur- 
 ing in bruises and injured places. The lesions are shallow, 
 rarely penetrating to the heart of the root, and the affected 
 tissue is quite firm and tough. Often at the center of the 
 spots small, black bodies are developed, which appear at 
 times as dense masses of small, black bristles. These are the 
 fruiting bodies or pycnidia of the fungus. Wetting the sur- 
 face of the lesion will bring out better these distinguishing 
 characteristics. 
 
 Black rot is of common occurrence in all sweet potato 
 regions. The roots become infected in the field, often 
 through wounds. The diseased areas may enlarge in stor- 
 age or transit, where overheating and lack of ventilation 
 favor the progress of the disease. "Generally, affected stock 
 is culled out and is not sent to the markets. 
 
 Affected stock is unfit for table use since the diseased 
 tissue is very bitter. When cooked, the entire root has a 
 bitter flavor. Diseased sweet potatoes also are unsuitable 
 for seed purposes, since black rot is spread by planting in- 
 fected seed roots. 
 
 Ref. (24); (27); (70). 
 
 SWEET POTATO: SOIL ROT. 
 
 Cause: A slime mold (Cystospora batata). 
 The symptoms of this disease are small, circular, sunken 
 spots about one-half inch in diameter in which the tissue 
 
64 U. S. DEPARTMENT OF AGRICULTURE. 
 
 has dried out and cracked. The lesions may appear as cir- 
 cular pits or depressions from which the diseased tissue has 
 fallen out. There may be some constriction of the root 
 where such lesions are located. 
 
 Infection occurs in the field and the disease does not pro- 
 gress in storage. 
 
 The economic importance of soil rot is due to the fact that 
 it reduces the yield and disfigures the roots. 
 
 Ref. (69). 
 
 SWEET POTATO: SCURF. 
 
 Cause: A fungus (Monilochaetes infuscans). 
 
 Scurf is marked by small, circular, dark clay-colored spots 
 on the skin of the root, which may unite to form large 
 blotches. The spots are only skin-deep. In advanced 
 stages, the skin turns to a deep brown color and becomes 
 wrinkled and rough. 
 
 Scurf occurs in practically all sweet potato growing 
 regions. 
 
 Infection takes place in the field, but the spots may de- 
 velop in storage. The disease does not spread from one root 
 to another. The market value of diseased stock is slightly 
 reduced because of its unsightliness. 
 
 Ref. (24); (27). 
 
 SWEET POTATO: SOFT ROT. 
 
 Cause: A fungus (Rhizopus nigricans) . 
 
 This rot is one of those elsewhere described as Rhizopus 
 rot. Soft rot develops very rapidly, and unless checked, 
 soon involves the whole root. In the early stages, the 
 affected tissue is soft, watery, and stringy, and yields a 
 brownish-yellow liquid when compressed. The early stage 
 is also attended by an odor of vinegar or acetic acid. Under 
 warm, moist conditions, the characteristic mycelium and 
 sporangia may appear on the outside of the root. The 
 affected tissue eventually becomes dry, shrunken, and yel- 
 lowish brown. At this stage an aromatic odor may be 
 detected. 
 
 Infection, which takes place through wounds, occurs 
 either in the field, in transit, or in storage and is favored by 
 high temperature and humidity. The rot progresses and 
 spreads very rapidly in transit and storage. Infection may 
 set in at the end or the middle of the root. In the former 
 case, it is called soft rot ; in the latter, if encircling the root, 
 ring rot. 
 
 Control consists of careful handling of the roots to avoid 
 wounds, careful sorting, proper curing, and storage in a dry 
 atmosphere at a temperature of 50 F. When wet weather 
 prevails during harvest, the shipment of roots not properly 
 dried often results in severe losses. An additional control 
 measure is the disinfection of storage houses and cars with 
 copper sulphate or formaldehyde. 
 
 Ref. (24); (27). 
 
MARKET DISEASES OF VEGETABLES. 65 
 
 SWEET POTATO: STEM ROT. 
 
 Cause : Fungi (Fusarium batatatis and F. hyperoxy- 
 sporum). 
 
 In stem rot the end of the root is light and shriveled, and 
 the interior has a deep brown color and a peculiar cinna- 
 mon odor. Usually, however, stem rot is not plainly visible 
 externally, and the disease manifests itself merely by a dis- 
 colored ring, and at times by a secondary ring, visible in 
 transverse sections of the root. If the outer part of the root 
 is carefully removed, the discolored parts appear as a net- 
 work of brown fibers surrounding the heart. 
 
 Stem rot is of widespread occurrence in all sweet potato 
 districts. 
 
 This disease causes a wilt of vines in the field, and re- 
 duces the yield. Infection of the roots takes place in the 
 field, and the disease progresses only slightly in storage. 
 Stem rot is found infrequently in the market, and is de- 
 scribed here principally to avoid confusion with freezing 
 injury, which it somewhat resembles. 
 
 Ref. (24). 
 
 SWEET POTATO: MISCELLANEOUS DISEASES. 
 
 DRY ROT. 
 
 Cause: Fungi (Fusarium species). 
 
 This disease is comparable to the Fusarium tuber rot of 
 the Irish potato. It is marked by shrunken areas showing 
 discolored flesh, and usually starts at one end of the root. 
 Dry rot is not common or of much importance. 
 
 FOOT ROT. 
 
 Cause : A fungus (Plenodomus destruens) . 
 
 This is a storage rot of some importance. It follows a 
 blighting of plants in the field. It is a firm brown rot with 
 pimple-like protuberances on the surface. Foot rot may 
 enter roots through wounds and bruises and thus cause some 
 loss in storage. 
 
 Ref. (27). 
 
 NEMATODE DISEASE. 
 
 (See Nematode Disease). 
 
 TOMATO: ANTHRACNOSE. 
 
 Cause: A fungus (Colletotrichum phomoides). 
 
 In its early stages, anthracnose is characterized by small, 
 circular, sunken spots of the same color as the sound tissue. 
 These lesions enlarge rapidly, become watersoaked and 
 more sunken, and bear pinkish spore heaps which often 
 coalesce to form a slimy layer. These spore heaps or acer- 
 vuli turn black at times and resemble the pycnidia of Phoma, 
 so that anthracnose may be mistaken for Phoma lesions. 
 However, the spore heaps never are as definitely rounded as 
 
66 U. S. DEPARTMENT OF AGRICULTURE. 
 
 the pycnidia, and the pycnidia never are pink. The centers 
 of anthracnose lesions are at first light brown, and do not 
 become as black and charry as those of Phoma rot. 
 
 Anthracnose is common on northern-grown tomatoes, 
 especially New Jersey stock. Green fruit is rarely affected. 
 
 The original infection takes place in the field. The dis- 
 ease develops in the field, and may also spread and develop 
 in transit and storage. Often this fungus destroys the entire 
 fruit. 
 
 It is advisable not to pack or ship infected fruit because 
 it rots rapidly and is a menace to healthy fruit. 
 
 Ref. (30). 
 
 TOMATO: BUCKEYE ROT. 
 
 Cause : A fungus (Phytophthora terrestria) . 
 
 No better description of this disease can be given, so far 
 as the appearance of the fruit on the vine or in transit is 
 concerned, than is implied by the name "buckeye." In color 
 and in its surface appearance, the diseased tissue resembles 
 a horse chestnut very closely. The color is grayish to brown, 
 and the surface is uneven, being sunken in places. The rot 
 at first is firm and even hard. The border is irregular and 
 not sharply defined, and often merges into water-soaked, 
 slightly bleached, green tissue. At times there appear 
 widely separated concentric rings of more or less irregular 
 wavy outline. These rings, however, are by no means a con- 
 stant accompaniment of the disease. Under moist condi- 
 tions the lesions generally are covered by a white, fluffy 
 growth of mold. 
 
 In case concentric rings are found in buckeye rot, they are 
 farther apart and less regular in outline than in soil rot. In 
 soil rot, the mycelium is brown and may produce sclerotia, 
 while the mycelium of buckeye rot is white and produces no 
 sclerotia. The absence of white, glistening or black spo- 
 rangia differentiates buckeye rot from Rhizopus rot. 
 
 This disease occurs most commonly in southern tomatoes 
 during rainy weather. The original infection takes place in 
 the field, and occurs only on fruit which has been in contact 
 with the soil or close enough to it to be spattered during 
 rains. 
 
 As in the case of soil rot, buckeye rot can be controlled 
 in the field by staking the vines to keep them off the ground. 
 At harvest it is advisable to sort out diseased fruit because 
 it is unsuitable for food and is a menace to healthy stock 
 since the fungus passes through the wrappers from diseased 
 to healthy fruit. 
 
 Ref. (56); (59). 
 
 TOMATO: NAIL-HEAD SPOT. 
 
 Cause: A fungus (Alternaria solani). 
 
MARKET DISEASES OF VEGETABLES. 67 
 
 In the early as well as the later stages, nail-head spot is 
 marked by small, dry, slightly though abruptly sunken scab- 
 like spots which are brown to black in color. 
 
 These spots or lesions generally are mere blemishes, and 
 cause little damage. The lesions may be circular or ellipti- 
 cal and at times may coalesce to form a large, irregularly 
 shaped area. At times the spots on ripening fruits are sur- 
 rounded by a green zone due to delayed ripening of the 
 bordering tissue. The tissue underlying the spot is not 
 affected, and the diseased tissue can easily be removed from 
 the sound tissue underneath. As the lesion ages, it often 
 cracks and opens the way for the entrance of secondary rots 
 such as Phoma. 
 
 The small size and the slightly sunken, flat and scab-like 
 nature of the lesions of nail-head differentiate these from 
 the lesions of other tomato fruit diseases, most of which, in 
 contrast, are large or water-soaked, often deeply sunken 
 and involve more rotting of the tissue. 
 
 Nail-head spot is a warm-weather disease, and is preva- 
 lent on fruit from the Gulf States. It is a serious field dis- 
 ease, attacking leaves, stems and fruits, and is known by the 
 growers as early blight. The fruit is infected before it 
 leaves the field, and the spots are visible when the fruit is 
 packed. The spots may enlarge slowly in transit and 
 storage. 
 
 Spraying will control the disease in the field. In packing 
 it is advisable to sort out spotted fruit because its presence 
 lowers the market value of a shipment and affected fruits 
 are predisposed to rots. 
 
 Ref. (56); (60). 
 
 TOMATO: PHOMA ROT. 
 
 Cause: A fungus (Phoma destructiva). 
 
 In its early stages, Phoma rot is marked on the green fruit 
 by minute, slightly sunken circular spots with a brown or 
 black border and a lighter center. Later the center of the 
 spot becomes covered with black pimple-like bodies. These 
 are known as pycnidia (singular pycnidum). In the early 
 stages, spots on ripe fruit are water-soaked and concave. 
 Later, as they enlarge, the centers become brown to charry 
 black, leathery and firm, and covered with pycnidia. The 
 borders are slightly sunken and water-soaked. The lesions 
 increase indefinitely and quite rapidly in size but remain 
 more or less circular and concave. 
 
 The lesions generally occur at the stem end of the tomato, 
 and the disease is often known as stem-end rot. The spots, 
 however, are not confined to this part of the fruit, as the 
 fungus may attack the fruit wherever it is bruised or in- 
 jured. The fungus may also enter through nailhead spots. 
 Until the lesion becomes very large, the underlying brown 
 or black tissue is quite firm. 
 
68 U. S. DEPARTMENT OF AGRICULTURE. 
 
 Without a microscope it is quite difficult at times to differ- 
 entiate the various rots of mature tomato fruits caused by 
 Phoma, Colletotrichum, and other fungi. This is especially 
 true when secondary rots have set in and covered up or con- 
 fused the typical clear-cut symptoms. 
 
 It appears, however, that anthracnose and other fruit rots 
 are more common on over-ripe fruit, and occur in southern 
 stock later in the season than does the Phoma rot. The 
 slimy, orange-pink spore masses of anthracnose aid in dif- 
 ferentiating it from Phoma rot. In Phoma rot, slimy spore 
 masses appear very frequently at the openings of the pycni- 
 dia, but these are whitish rather than pink in color. 
 
 This disease is most marked in southern winter-grown 
 tomatoes; that is, the Cuba, Florida, and California crops. 
 It was exceedingly destructive to Cuban tomatoes during 
 the winter of 1917-18, and to Florida tomatoes during April 
 and May of the same season. 
 
 The disease occurs on the vines, where it is known as 
 Phoma blight or black spot. It is not known definitely 
 whether the original infection of the fruit destroyed in tran- 
 sit occurs in the field or in the packing house. The disease 
 develops in transit and in the ripening rooms, and is favored 
 by a warm, moist atmosphere. 
 
 Affected fruit is subject to infection with bacteria and 
 other fungi. 
 
 No satisfactory control of the disease in transit and in the 
 ripening rooms has been worked out. 
 
 Ref. (32); (56); (60). 
 
 TOMATO: SOIL ROT. 
 
 Cause: A fungus (Rhizoctonia). 
 
 In its early stages, soil rot on green or ripe fruit is char- 
 acterized by firm, brown spots which may be marked with 
 concentric rings. Later they increase in size and generally 
 a brown, firm mat of mold covers the older lesions. On 
 mature fruit in the market, soil rot lesions are large, brown, 
 water-soaked areas not sunken and not concentrically 
 marked. 
 
 Soil rot progresses and spreads very rapidly in transit and 
 storage, the fungus passing from one fruit to another 
 through the wrappers. The most striking characteristic 
 under these circumstances is the plentiful development of a 
 coarse, white, and later, brown mycelium with small brown 
 sclerotia. The growth of the hyphae is of a peculiar radiat- 
 ing type, resembling densely crowded spokes of a wheel, 
 and is often further characterized by concentric zones. Very 
 often the mycelium, the sclerotia, and the paper wrapper 
 form a thick, dry and hard mat, or the hyphae may hold the 
 wrapper quite firmly to the fruit so that shreds of it remain 
 when the fruit is unwrapped. Examination of decayed fruit 
 in the market often reveals the original soil rot lesion with 
 its firm, brown and concentrically marked center surrounded 
 
MARKET DISEASES OF VEGETABLES. 69 
 
 by water-soaked but firm tissue. Later there appears the 
 coarse white mycelium which turns brown and forms scler- 
 otia. The water-soaked areas are often referred to by the 
 trade as "water blisters." 
 
 The fact that this rot is not limited to the blossom-end of 
 the fruit, and is accompanied by a mycelium, differentiates 
 it from blossom-end rot. It may follow blossom-end rot, 
 however. Its solid mat of brown mycelium and its large 
 lesions differentiate it from nail-head spot. The brown mat 
 of fungus and the more regular and more closely arranged 
 markings also differentiate soil rot from the buckeye rot. 
 Furthermore, in the field, soil rot always shows these con- 
 centric rings while buckeye rot may not. Soil rot differs 
 from Phoma rot by the absence of a black center with black 
 pycnidia and from anthracnose by the absence of the 
 orange-pink spore heaps. 
 
 Soil rot is especially severe on Florida tomatoes during 
 rainy weather. It also occurs in early shipments of Cali- 
 fornia tomatoes. 
 
 The original infection takes place from the soil in the 
 field. Fruits touching the ground or hanging low enough 
 to be spattered by the soil during rains are infected. The 
 rot develops and spreads in the pack. 
 
 This disease can be controlled in the field by staking the 
 plants. It is advisable to sort out diseased fruit in the pack- 
 ing house, since affected fruit is unmarketable, unfit for 
 food, and a menace to sound fruit. 
 
 Ref. (56). 
 
 TOMATO: BLOSSOM-END ROT. 
 
 Cause: Non-parasitic (probably irregular water supply). 
 
 In the early stages this disease appears as a small spot at 
 the blossom-end, or it may involve the whole blossom sur- 
 face of the fruit. At this stage the spot looks like a bruise, 
 is dark green in color and water-soaked. Later it becomes 
 darker, and the affected tissue collapses and becomes firm 
 and leathery. Sometimes the collapse is so sharply marked 
 that the lesion appears as a distinct depression. Generally, 
 however, it results only in a flattening of the end of the fruit. 
 The lesions are very shallow and dry ; this, together with the 
 restriction of this injury to the blossom-end, serves to differ- 
 entiate blossom-end rot from the buckeye rot of green toma- 
 toes and the soil rot of both green and ripe fruits with which 
 it might be confused. 
 
 Blossom-end rot is a field disease, and occurs in all tomato 
 growing districts. 
 
 Affected tissue is predisposed to secondary rots, which 
 develop in the field, in transit, and in storage. The non- 
 parasitic injury is, in fact, commonly followed by fungous 
 rots. 
 
 Blossom-end rot has not been successfully controlled. 
 Regulation of the water supply, and the use of varieties 
 
70 U. S. DEPARTMENT OF AGRICULTURE. 
 
 suited to the soil and climate, are important points to con- 
 sider. 
 
 It is not advisable to put badly affected fruit on the mar- 
 ket. Slightly affected fruit, if not infected by fungi, can be 
 used for food. 
 
 Ref. (3). 
 
 TOMATO: MOTTLING. 
 
 Cause : Unknown, probably mosaic. 
 
 This disease is characterized by a more or less extensive 
 brown discoloration of the surface of the fruit in which the 
 affected areas show great diversity of pattern, such as cir- 
 cular spots, blotches, loops, and streaks. The affected areas 
 are somewhat sunken and on green fruits the brown color 
 may be absent. The affected tissue is firm and hard. The 
 entire thickness of the wall and even portions of the septa 
 (partitions) are involved. It seems that portions at least 
 of the affected tissues are dead. At any rate, diseased fruits 
 will not ripen properly in the ripening rooms, and the 
 browned or sunken areas commonly become infected with 
 various fungi. * The disease resembles in some ways the 
 mosaic disease of cucumbers. 
 
 In shipments of California tomatoes received in Chicago 
 during the fall of 1918, this disease was undoubtedly the 
 most important loss-producing factor, the loss amounting in 
 some cases to 50 per cent or more. 
 
 No control is known. Since the symptoms are evident on 
 the green fruits, it is advisable to sort out affected stock 
 before shipment, as it is a total loss at destination. 
 
 TOMATO: BLACK ROT. 
 
 Cause: A fungus (Alternaria). 
 
 The most striking symptom of this disease is the conspicu- 
 ous, black velvety growth of the fungus on the lesions. The 
 disease generally occurs on ripe fruit, where it causes a 
 slowly progressing rot. The fungus probably gains entry 
 through wounds and growth cracks. 
 
 TOMATO: CATFACE. 
 
 Cause : Unknown, probably varietal. 
 
 In this disease the blossom end of the fruit is badly mis- 
 shapen or puckered, probably due to the imperfect develop- 
 ment of an area which at maturity is represented by an 
 irregular leathery scar. Occasionally secondary rots occur 
 in the malformed areas. The presence of catface in ship- 
 ments lowers their market value. 
 
 TOMATO: GROWTH CRACKS. 
 
 Cause : Probably arrested and resumed growth. 
 These are rather deep ruptures or cracks radiating from 
 the stem end. Occasionally they are arranged concentric- 
 
MARKET DISEASES OF VEGETABLES. 71 
 
 ally about the stem end. They seldom, if ever, occur in the 
 blossom half of the fruit. 
 
 These cracks are actual wounds. Either before or after 
 the fruit leaves the field, they 'are very likely to become in- 
 fected with rot-producing organisms. From the market 
 point of view, growth cracks assume a very great impor- 
 tance because rots so frequently start in them. 
 
 TOMATO: RING ROT. 
 
 Cause: A fungus (Melanconium). 
 
 A large, circular, flattened lesion, very conspicuous be- 
 cause of its broad, concentric rings, is characteristic of this 
 disease. The background color is brown and the center and 
 the margin may be slightly elevated. Under moist condi- 
 tions acervuli (singular acervulus) , the fruiting bodies of the 
 fungus, appear. The spores which exude from them fre- 
 quently germinate and the resultant white mycelial growth 
 covers the center of the lesions. The rotted tissue is firm, 
 but affected fruits are worthless. Ring rot has been found 
 to a limited extent in Cuban tomatoes. 
 
 Ref. (72a). 
 
 TOMATO: FUSARIUM ROT. 
 
 Cause: A fungus (Fusarium). 
 
 The differentiating symptom of this disease is a heavy, 
 compact, pinkish-white growth of the fungus on the lesions. 
 The advancing edge of the lesions frequently is free from 
 visible fungous growth and is water-soaked and shrunken. 
 The fungus probably attacks the fruit through wounds. 
 
 TOMATO: RHIZOPUS ROT. 
 
 Cause: A fungus (Rhizopus nigricans). 
 
 The general features of this disease have been taken up 
 under the discussion of Rhizopus rot. It is a very soft, leaky 
 rot. Affected fruit has an acid odor and when ripe usually 
 has a bleached appearance. This rot rarely is found on 
 green fruit. 
 
 The fungus attacks the fruit through breaks in the skin. 
 These may be due to careless handling and so minute as to 
 be invisible to the unaided eye, or they may result from skin 
 pricks, nail injury, or mashing in packing or transit. The 
 disease spreads in transit, the fungus growing through the 
 wrapper from diseased to healthy fruit. 
 
 Ref. (56). 
 
 TOMATO: FOUL-SMELLING ROTS. 
 
 Cause: Bacteria and fungi. 
 
 The various tomato rots that are accompanied by foul 
 odors have not been studied sufficiently to be differentiated 
 and named. 
 
 TOMATO: SUN-SCALD. 
 
 (See Sun-scald). 
 
72 U. S. DEPARTMENT OF AGRICULTURE. 
 
 TURNIP: GRAY MOLD ROT; BOTRYTIS ROT. 
 
 (See Gray Mold Rot). 
 TURNIP: SLIMY SOFT ROT; BACTERIAL ROT; SOFT ROT. 
 
 (See Slimy Soft Rot). 
 
 WATERMELON: ANTHRACNOSE. 
 
 Cause: A fungus (Colletotrichum lagenarium). 
 
 In its early stages, anthracnose is characterized by small 
 circular raised welts on the rind, dark green in color. As 
 these increase in size, the centers turn brown, become 
 sunken, and under moist conditions the pink acervuli of the 
 fungus are formed. As a lesion enlarges, the center becomes 
 more sunken, often turns black, and eventually the surface 
 cracks, exposing the rotted tissue or a cavity underneath. 
 The fungus causes a rather slowly advancing dry rot of the 
 rind tissue, and finally penetrates the edible pulp. Under 
 extremely dry, hot conditions, such as occur in California 
 during the melon harvest, the lesions may remain in the 
 blister or nail-head stage. 
 
 Anthracnose is a serious disease of the vines and fruits in 
 the field. The fungus is spread with the seed, overwinters 
 in the soil, and spreads in the field during rainy weather. 
 This is the same fungus which causes cucumber and musk- 
 melon anthracnose. 
 
 Many fruits are rendered worthless in the field. The dis- 
 ease is also present in almost every car of melons shipped 
 north as a result of field infection which may or may not 
 have been detectable at the time of loading. The lesions 
 enlarge during transit and not only seriously impair the 
 appearance of the fruit, but open the way for the entrance 
 of other rot-producing organisms. 
 
 Anthracnose is prevalent throughout the southern melon 
 regions and the Ohio Valley. It is the source of great losses 
 in the field, in transit, and in the market. 
 
 The disease can be controlled in the field by crop rotation, 
 use of disease-free seed, and spraying with Bordeaux mix- 
 ture. 
 
 Ref. (58). 
 
 WATERMELON: STEM-END ROT. 
 
 Cause: A fungus (Diplodia). 
 
 This is a rapidly progressing soft rot of the stem end of 
 the melon, marked externally by a brown discoloration and 
 shrivelling followed by the development of abundant black 
 pycnidia or a dark, gray, moldy outgrowth of the fungus. 
 Whitish spore masses are often discharged from the pycni- 
 dia. The disease usually affects the stem-end of fruit, but 
 occurs also at wounds and, in the field, as a blossom-end rot. 
 
 While the rot is rather common in the field, diseased 
 fruits are not often shipped,, and it seems quite likely that 
 
MARKET DISEASES OF VEGETABLES. 73 
 
 infection in the case of the stem-end rot found in the market 
 takes place through the end of the stem after it is cut. The 
 rot then develops with extreme rapidity during transit. 
 
 This is the most important rot of watermelons, and is 
 rather general in southern grown stock, causing very heavy 
 losses in some cars. 
 
 Stem-end rot as it occurs in transit can be prevented by 
 proper treatment of the melons at the time of loading. After 
 a tier of melons is in place, the ends of the stems are cut off 
 and a paste made of starch and copper sulphate is applied 
 to the freshly cut surfaces. This prevents infection by the 
 fungus. 
 
 Ref. (42); (51). 
 
 WATERMELON: MISCELLANEOUS DISEASES. 
 BLOSSOM-END ROT. 
 
 Cause: Unknown (not parasitic). 
 
 This disease appears as a flattened, dry, leathery, black- 
 ened spot about as big as a silver dollar, at the blossom-end 
 of the fruit. The tissues underneath are sound unless the 
 killed area becomes infected with some fungus such as the 
 Diplodia of stem-end rot, which is a common secondary 
 invader. 
 
 While the cause of this trouble has not been demon- 
 strated, it is quite likely that it is due to an unbalanced 
 water supply as in the similar disease of tomatoes. Although 
 of minor importance in the market, it may .open the way to 
 rot-producing fungi. 
 
 Ref. (51). 
 
 CHEMICAL INJURY AND ABRASION. 
 
 Cause : Contact with the walls or floors of cars. 
 
 This injury consists of large brown sunken areas or 
 gouged channels in the rind. It is most common in cars 
 previously used for chemicals such as fertilizers, especially 
 where some shifting of the load has occurred. Sometimes 
 fungi gain entrance through these injuries, and cause decay. 
 
 Compared with stem-end rot, this trouble is not of com- 
 mon occurrence. 
 
 Ref. (51).