CALIFORNIA AGRICULTURAL EXTENSION SERVICE CIRCULAR 103 JANUARY, 1937 ALMOND CULTURE IN CALIFORNIA MILO N.WOOD The Bureau of Plant Industry, United States Depart- ment of Agriculture in cooperation with the College of Agriculture, University of California Cooperative Extension work in Agriculture and Home Economic College of Agriculture, University of California, and United States Department c riculture cooperating. Distributed in furtherance of the Acts of Congress of T and June 30, 1914. B. H. Crocheron, Director, California Agricultural '. ?nsion Service. THE COLLEGE OF AGRICULTURE UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA CONTENTS PAGE Introduction 3 Characteristics and habits of growth 3 Acreage and yields of almonds 5 Climatic requirements 12 Heat requirements 12 Hardiness and temperature 12 Atmospheric humidity and rainfall 17 Soil requirements 17 Varieties 20 Choice of varieties 20 The relation of varieties to the market and to the grower 22 The utilization of almond kernels as affecting demand for varieties 23 Groups of varieties from the marketing standpoint 24 Varieties recommended for planting in California 25 Pollination 29 Rootstocks 35 Propagation and top-working 40 Establishing the orchard 40 Orchard operations 45 Cultivation 45 Intercrops 46 Covercrops 47 Irrigation 48 Drainage 54 Fertilization 54 Pruning 56 Rejuvenation of old trees 62 Almond diseases 63 Parasitic diseases 63 Nonparasitic diseases 70 Insects and other pests of almonds 71 Summary of spray programs 79 Crop harvesting and handling 79 Marketing 96 ALMOND CULTURE IN CALIFORNIA' MILO N. WOOD 2 INTRODUCTION The almond (Amygdalus communis), like many other orchard fruits, is of obscure origin. The so-called wild almonds, found very early in the Eastern Hemisphere, were probably the ancestors of the first cultivated varieties. At any rate, almond growing early became an important branch of agricultural endeavor. At present the almond is grown to some extent in many of the warmer regions of the world, especially around the Mediterranean Sea, where both bitter and sweet nuts are produced in large quantities. Attempts have been made to grow the almond in nearly every agricul- tural region. In our own country the edible almond has been widely tested, but most of the early plantings failed. Because of its exacting climatic requirements, this nut can be grown profitably only in the most favored districts. At present practically all the almonds grown commer- cially in the United States come from California. CHARACTERISTICS AND HABITS OF GROWTH The almond tree somewhat resembles the peach in manner of growth and in character of leaves and blossoms. The differences, however, can be recognized even by the inexperienced. The almond tree is one of the earliest to bloom in the spring and commonly produces blossoms in pro- fusion before the foliage develops (fig. 1) . The first leaves appear about the time the last petals fall, although this close sequence depends some- what on the variety and the season. The leaves develop rapidly, and the tree is soon in full foliage. The resemblance of the fruit to the peach is soon apparent. Its thin, leathery hull 3 corresponds to the thick, fleshy portion of the peach, but it is nonedible and splits open when mature, exposing the nut inside (fig. 2). 1 In 1918, the California Agricultural Experiment Station published Bulletin 297, The Almond in California, by E. H. Taylor. This bulletin was revised in 1925 by G. L. Philp and published as Circular 284, under the same title. The present circular retains such information from these two publications as is now considered useful and adds much new material to bring the subject up to date. 2 Milo N. Wood, Pomologist, Division of Fruit and Vegetable Crops and Diseases, Bureau of Plant Industry, United States Department of Agriculture. 3 Botanically the hull is the mesocarp and exocarp of the pericarp. [3J California Agricultural Extension Service [Cir. 10; Fig. 1. — Almond trees in full bloom. Note the profusion of blossoms. '*'.*- P nod 1 1 ■,y . =:■ ■: n - ;%, ■■■v^ *tf «* Fig. 2. — Almonds on the tree, showing bearing habit. Note the splitting of the hulls. Almond Culture in California ACREAGE AND YIELDS OF ALMONDS The almond is grown commercially in various districts in California. The Pacific Ocean, the prevailing winds, and the mountain ranges cause the thermal or heat belts to run north and south rather than east and west, so that latitude does not limit crop production as in other parts of the United States. Almonds are grown from Shasta County in the north to Riverside and San Diego counties in the south, this belt being approxi- mately 700 miles long, a distance equal to that from the southern bound- ary of New York to central Georgia. The main producing areas are in EACH DOT EQUALS 400 ACRES ; COUNTIES WITH LESS HAVE ONE DOT. Fig. 3. -Almond-growing districts in California. The dotted areas show the main districts. California Agricultural Extension Service [Cir. 103 the great Sacramento and San Joaquin valleys, extending eastward and westward into the adjacent foothills. Orchards are found also in various smaller valleys (fig. 3). The total bearing and nonbearing acreage of almonds in California is about 85,000 acres. The separation of bearing from non-bearing acre- TABLE 1 Almond Acreage, Production, Value, and Yield Per Acre in California Year Bearing acreage Production in the shell Total value Value per ton Value per pound in the shell Average yield per acre / 2 3 4 5 6 7 1914 1915 1916 1917 1918 14,947 18,602 20,470 28,383 29,242 30,100 35,044 41,184 51,496 56,922 60,962 68,021 73,644 61,104 70,201 71,856 71,516 71,070 70,897 72,300 71,804 72,000f 61,771 tons 2,250 3,500 3,400 4,000 5,100 7,250 5,500 6,000 8,500 11,000 8,000 7,500 16,000 12,000 14,000 4,700 13,500 14,800 14,000 12,900 10,900 9,100 10,332 dollars dollars 440 360 320 290 260 300 400 300 320 340 480 200 176 165 186 180 208 289.70 cents 22.00 18 00 16 00 14 50 13 00 15 00 20 00 15 00 1600 17 00 24 00 10 00 8.30 8 25 8 30 9 00 10 40 14 40 pounds 301 376 332 282 349 1919 3,190,000 1,980,000 1,920,000 2,465,000 2,860,000 2,400,000 3,000,000 4,800,000 3,840,000 4,760,000 2,256,000 2,700,000 2,604,800 2,310,000 2,399,400 1,962,000 1,892,800 2,784,705 482 1920 314 1921 1922 291 330 1923 386 1924 262 1925 1926 220 434 1927 1928 393 399 1929 131 1930 377 1931 1932 1933 416 395 357 1934 304 1935 Average! 253 337 9 * Dashes indicate data not available. t Estimated. t All averages for seventeen years (1919-1935 inclusive). Sources of data: Col. 2: 1914-1920: Compiled from California Almond Growers' Exchange Minute Book, various 1921-1926: Kaufman, E. E. California crop report for 1928. California State Dept. Agr. Special Pub. 96:1-68. 1929. 1927-1933: Blair, R. E., and E. E. Kaufman. Acreage estimates for California fruit and nut crops 1927-1932. California State Dept. Agr. Special Pub. 117:1-32. 1932. Cols. 8, 4, and 5: U. S. Dept. Agr. Yearbooks of Agriculture 1931, 1932, 1934, and 1935. age is difficult because opinions differ as to the proper age and size of a tree and number of crops it should bear before it is really in the bearing- class. The bearing acreage is now estimated at 70,000 to 80,000 acres. The California Crop Reporting Service (1936) places it at 71,804. The data in table 1 show the changes in bearing acreage for the last twenty-two years (1914-1935). Although in certain periods new plant- Almond Culture in California 7 ings have been extensive, most of the increase in bearing acreage has been gradual. The data show, however, a great development, the acreage for 1935 being approximately five times that for 1914. The industry on the whole, therefore, has expanded enormously. The annual production of almonds in tons is given over a period of twenty-two years in table 1, column 3. The average for the last seventeen years (1919-1935) is 10,332 tons annually, or 20,664,000 pounds in the TABLE 2 California Almond Crop Compared with United States Imports Season Imports in kernel form Imports in the shell converted to kernel weights* Total imports kernel weights Weights of kernels of California production t Total U. S. supply kernel weights California crop as per cent of U. S. supply 1921-22 tons 12,851 11,700 12,021 9,877 9,759 8,067 9,098 8,694 9,503 6,238 3,905 2,317 1,414 1,635 tons 963 722 479 628 614 80 140 261 904 9 2 24 3 1 tons 13,814 12,422 12,500 10,505 10,373 8,147 9,238 8,955 10,407 6,247 3,907 2,341 1,417 1,636 tons 2,700 3,825 4,950 3,600 3,375 7,200 5,400 6,300 2,116 6,075 6,660 6,300 5,805 4,905 tons 16,514 16,247 17,450 14,105 13,748 15,347 14,638 15,255 12,522 12,322 10,627 8,641 7,220 6,541 per cent 16 3 1922-23... 23.5 1923-24 . . 28.4 1924-25 . 25 5 1925-26 24 5 1926-27 46.9 1927-28 36 9 1928-29 1929-30 41 3 16.9 1930-31 1931-32 1932-33 . 49.3 82.7 73.0 1933-34 80.5 1934-35 75 * Converted on the assumption that the nuts contained 33)^ per cent kernels, t Converted on the assumption that the nuts contained 45 per cent kernels. Source of data: Compiled from: Federal-State Market News Service. Almond market information bulletin No. 122:1-10. Sacramento, California. July 6, 1934. (Mimeo.) shell. The largest figure for the period was 16,000 tons (32,000,000 pounds) for 1926, and the lowest 4,700 tons (9,400,000 pounds) for 1929. Since most almonds are retailed as kernels, it is interesting to convert their weights in the shell to the weights of the kernels after shelling. The Federal-State Market News Service has made this calculation for both imported and California almonds. The data in table 2 show that from 1922 to 1934 the imports of almonds decreased markedly. There was also a decrease in the total supply of kernels used in the United States during the last five years as compared with the first five years of this period. The percentage of the total supply of kernels for the United States pro- duced by California has greatly increased, however, during the period. Although exact figures are lacking, the world production is exceed- ingly large ; and the total for California is so small, by comparison, as California Agricultural Extension Service [ Cir - 103 to have no widely felt influence on the world market. When foreign mar- kets are good, most of the foreign almonds may be consumed abroad at a good price. When markets abroad are dull and low prices prevail, for- eign countries may export to the United States in great quantities, which may affect the price of domestic almonds. This circular will not consider the tariff and other factors affecting prices, but will merely note that with almonds the world price depends more upon the world's supply than upon the relatively small California production and that the TABLE 3 Classification of 149 Orchards According to Yield for 1925 Average yields Number of orchards Average cost of production per pound Acreage Per cent of acreage pounds 44 43 29 19 14 cents 35.3 14 .6 10 7 9.8 6 8 1,755 35 1,278.85 803 98 525 00 214 00 per cent 38 250 to 500 28 500 to 750 18 750 to 1,000 11 1.000 and over 5 Source of data: Adams, R. L. Cost of producing almonds in California. A progress report. California Agr. Exp. Sta. Bui. 422:49. Table 20. 1927. climatic limitations are so great that there is much less danger of over- production than with most other crops in the United States. The yield per acre is important in determining whether an orchard is profitable. The cost of production per pound of nuts is always higher in the low-producing orchards. The average yield per acre of almonds in California — much lower than is generally realized — is obtained in table 1, column 7, by dividing the total yields in pounds by the total number of bearing acres. For seventeen years the average annual yield was 337.9 pounds. According to Adams' data 4 the average yield per acre is slightly higher. From 1921 to 1925 it was computed to be 505 pounds. Adams segregated 149 orchards, comprising 4,577 acres, on the basis of different yields (table 3). In these orchards, high yields are the exception. Data collected by the writer from 1920 to 1930, including many poor orchards along with the good ones, show that the average annual yield per acre from 35,174 acres was only 183 pounds. According to all the records available, the average yield is very low ; and if such yields are multiplied by the price per pound, the average income per acre is so low that there has been no average profit. Such fig- 4 Adams, R. L. Cost of producing almonds in California. A progress report. Cali- fornia Agr. Exp. Sta. Bui. 422:1-52. 1927. (Out of print.) Almond Culture in California 9 ures, however, indicate the worst rather than the normal possibilities. To apply to all conditions, the yields must be segregated so as to average separately the young orchards, the old orchards, and the low-producing orchards. The averages as given, therefore, are useful mainly in show- ing that there is a large acreage just coming into bearing, or a large acreage growing almonds where they should never have been planted, or both. Many almond orchards, in fact, are on a paying basis, and a consider- able acreage produces well. Occasional orchards have produced over 1% tons ; some as much as a ton ; a large number % of a ton ; and a still larger number % ton or more per acre. In general, a really profitable orchard must produce at least % ton per acre but in certain larger orchards where the overhead is low, a profit may be made on a smaller yield. Clearly, however, almond orchards should not be planted where very low yields will prevail year after year. Several factors besides yield affect profit or loss — for example, initial investment and expense of developing the orchard before it comes into bearing; expense of upkeep after the orchard begins to bear commer- cially ; demand, prices, and costs of marketing. To some extent the grower controls certain factors affecting the cost of production. Lack of data and the variability of individual orchards and management make it difficult to give average cost data that will be generally applicable. Even in the few cases where fairly complete costs have been obtained for certain localities, the factors involved are so com- plex that the grower must interpret each item with special reference to similar items in his own orchard and must allow for conditions that may be different. Average costs of production for limited areas are valuable in showing what items may be considered in figuring out profits or losses for orchards in the locality. The data in table 4 give a five-year record obtained in Butte County for seven common varieties arranged in order of decreasing net profit or increasing net loss per acre. The number of records, number of acres, and period covered give a fairly good cross section of the industry in the district. The data were obtained, however, only on fifteen, sixteen, and seventeen-year-old trees and are therefore not applicable to younger or older ones, as a grower having trees of dif- ferent ages from those given must remember in applying the data to his orchard. The data show clearly the relation of price per pound, yield per acre, costs of labor, harvesting, materials, interest, and depreciation to profit or loss. The amount of interest (at 6 per cent) indicates that the value placed on the orchards is moderate ; from that important stand- point the growers have the advantage over those on high-priced land. 10 California Agricultural Extension Service [ Cir - 103 - I _t^t^ — 5 0) OT3 >- m a>% <-, 03 bt>-~ -0_ as o3 3 O > > Tt> OS »0 ©~*© OS 00 -h t- -<»< CO-* >0 t» t-- SS OlNWX CO c© oec a rH«t»» OO TJ-CO o^ t- oeos n wmNw 1-1 so ■O CO co a NlSM | O- o ® o -S 8 ^ if?! > > « CO I CT5 OO O OO CO 188 lOiO O CO >o 00 CO I^CO COO 1 CNaco | -«f co ss s J3 OS £ X5 > 5s h£ II 8S « o3 ; 33 03 y3 «j Oi-J O SI** 0Q c o^ 3 o gfi X-S ws o3 • Hco 3co =) . T & flt* .ssw © a as 93°"S i° 5-° Almond Culture in California 11 The total cash costs per acre are fairly uniform for the several varieties. The yield per acre and the price per pound were important in relation to profit or loss. The Nonpareil variety, though fifth in yield was the most profitable because it was highest in price, as is generally the case because of its thin shell, high percentage of kernel, and good quality. The I. X. L. variety, though second in price, was produced at a loss be- cause of low yield. The Peerless, a hardshell variety was the highest yielder, but next to the lowest in price. It was produced at a profit, how- TABLE 5 Average Cost of Production by Varieties for the Three-Year Period 1928-1930 Texas Nonpareil I.X.L. Ne Plus Ultra Drake 29 220 17 1,255 67 29 346 08 608 89 11 101 73 550 67 13 54 51 705.76 30 Total acreage Yield, pounds per acre 352 11 648.69 Dollars per acre Income 162 93 114 00 48 93 149 87 105 69 44.16 116 28 96 23 20 05 120 57 103 48 17.09 92.18 102 23 -10 05* Cents per pound Income Cost 12 8 8.98 3.82 21 4 15 1 6 3 21 1 17 48 3.62 17 08 14.66 2.42 14.19 15.76 -1 57 * The minus sign indicates loss. Source of data: Farm Management Specialist Agricultural Extension Service. Third annual report and three-year summary of almond efficiency study for Stanislaus County, 1930. p. 8. Table 6. California Agr. Ext. Serv. 1930. (Mimeo.) ever, because of its heavy yield in the district. The Nonpareil, Peerless, and Texas were the only varieties produced at a profit over the five-year period, whereas the Drake, Ne Plus Ultra, I. X. L., and Bidwell brought a loss. In table 5 are given cost data for a three-year average in another dis- trict, under conditions somewhat different from those in table 4. The Texas variety, being the heaviest yielder and the nuts being produced at the lowest price per pound, was the most profitable per acre of the five varieties even though it was sold at the lowest price per pound. The Non- pareil brought the highest net profit per pound, but ranked second in profit per acre because it yielded much less than the Texas. All the varieties were produced at a profit in the district except the Drake, which involved a loss. These data show the cost per acre to be somewhat less than that shown for Butte County (table 4). 12 California Agricultural Extension Service [ Cir - 103 The data in tables 4 and 5, though useful, were obtained from a small number of orchards and do not take all conditions into consideration. They are presented as the best obtainable and should be considered as giving an indication of the costs and returns that might be expected under similar conditions. Factors affecting costs of production, prices, and markets are further treated in a bulletin by Wellman and Braun. 5 CLIMATIC REQUIREMENTS The exacting climatic requirements of the almond limit its commercial production to very small portions of our country. Even within tested almond-growing districts, only well-adapted sites should be planted. The early plantings were made before much information was available re- garding the factors limiting production. Although the extensive com- mercial plantings in many sections, especially in California and Utah, often brought financial loss, they demonstrated that many sections could not grow almonds profitably and that only in favored localities with a suitable climate could success be expected. The information thus ob- tained has not always been considered in establishing orchards in recent years. Probably one-third of the present acreage will prove so unprofit- able that such orchards will have to be discontinued. HEAT REQUIREMENTS The almond requires a rather large number of heat units, and is well adapted to the hot interior valleys of California, where the nuts grow and mature satisfactorily. Because of the comparatively dry atmos- pheric conditions in these valleys the trees are less subject to diseases than along the coast. Although good crops have sometimes been obtained in the coastal districts, most of the plantings there have disappeared ; almonds should not be grown commercially where cool, foggy summers prevail. HARDINESS AND TEMPERATURE The almond tree, being about as hardy as the peach, can be grown over a wide area. The production of a crop, however, is an entirely different matter : the almond blooms so early that its blossoms are liable to frost injury — probably the most important factor in limiting the commercial production to well-defined areas. The degree of frost that will cause damage varies with the stage of development of the flower or young fruit and with the duration of the frost. Buds and blossoms weakened by lack of moisture, severe attacks 5 Wellman, H. R., and E. W. Braun. Almonds. California Agr. Exp. Sta. Bui. 453: 1-34. 1928. (Out of print.) Almond Culture in California 13 of the red spider, or early defoliation during the preceding summer, may be more susceptible to frost than vigorous buds and blossoms. Studies of healthy almond trees at the University Farm, Davis, showed the first differentiation of fruit buds of the I. X. L. variety on August 18, 1915 ; but the flower was not completely developed in the bud until February 18, 1916. Development proceeded unchecked through the winter even though the trees were apparently dormant. Evidently the leaves should remain on the tree until late in the fall so that food materials may be elaborated and stored for the buds to use in their normal development through the winter. If the leaves turn yellow or drop soon after harvest, the trees are generally unable to store enough food materials for their normal requirements, and the buds are insufficiently nourished during the winter. In the spring such buds are apparently unable to endure light frosts, continued cold weather, or sudden changes in temperature. The most tender stage in the blossoming and development of the young fruit seems to be shortly after the dropping of the calyx or husk. The blossom becomes more and more tender as it opens. Blossoms with petals exposed but not yet opened have been known to withstand 24° F for a short time, and those with petals beginning to fall have withstood 28°. In other cases, blossoms with petals falling have been killed by temperatures of 30° to 31°. The duration of the cold has an important bearing on the injury sustained. Often blossoms can withstand 26° or 28° for a short time ; but after a number of hours, damage occurs. Furthermore, blos- soms of some varieties such as the Nonpareil will withstand more frost in the early opening stage than others ; for example, the Peerless. The almond, blossoming so early, is often subjected to much more severe frosts than most other orchard crops. The greatest injury is apt to occur when the frost follows one or more days of warm weather. When the temperature remains low during both day and night, frosts that might otherwise kill the flowers or the setting fruits may do no harm. Adequate air drainage and freedom from frost are closely related (fig. 4). The lands along the lower foothills immediately above the floor of the valleys and the lands along the built-up banks of rivers are less subject to frost because the cold air flows from them to the lower lands adjacent. For this reason, almonds should not be planted on the lower lands of even the larger valleys. An exception may be a locality thor- oughly tested as to frost occurrence for a long period of years and proved frost-free because of some peculiar situation favoring air currents or air drainage, such as might exist near a natural draw in the hills where the settling of the cold air in some portions of the adjacent valley might be prevented. Such locations are generally confined to very small areas. 14 California Agricultural Extension Service [Cm. 10; Sometimes an opening or draw in the hills may drain the cold air from considerably higher elevations beyond, and thus greatly increase the danger from frost. This is common where canyons drain the cold air from the high Sierras to the valleys below. Elevated lands opposite draws in the hills above them must be carefully avoided unless known to be reasonably frost-free. In the larger valleys, even a gentle slope may result in proper air drainage provided there is a sufficiently long slope Fig. 4. — Almond orchards on rolling hills. On elevations of this nature the air drainage is good, and the orchards are comparatively free from frost. The draws to the right and left of the picture remove the cold air. Because of frost hazard, it is not safe to plant almonds on the lower land. Sloping lands like this also drain rapidly, with little danger of the soil becoming water-logged. Cultural operations, however, on such slopes are more difficult and expensive than on level land. below the orchard to carry off the cold air. Rows of trees or ridges often obstruct air currents and therefore interfere with proper air drainage. Variable weather conditions, especially as regards temperature in the spring after growth begins, sometimes injure the young fruits. Most of the dropping of fruits the size of peas or larger, however, is probably due to improper pollination. Frost injury is most apt to occur during clear nights with a dry atmos- phere, which favor the radiation of heat. Moist, cloudy nights tend to prevent a rapid fall of the temperature. Since winds or air currents mix warm air with the cold, frost seldom occurs in windy weather. Growers have attempted to prevent injury from frosts in three ways: (1) by irrigating, (2) by stirring up the air, and (3) by raising the temperature. Irrigation for Frost Prevention. — In recent years growers have been interested in applying water by irrigation during the time frosts occur as a possible means of raising the temperature. Observation seems to indicate that irrigation during light frosts has raised the temperature Almond Culture in California 15 enough to prevent injury. Irrigation facilities must be such, however, that the entire orchard can be irrigated in a few hours. From a practical standpoint the method is applicable to only a few orchards and cannot be generally recommended. Stirring Up the Air to Prevent Frost. — Recently there has been con- siderable experimenting with large and powerful fans which draw the warm upper air down and mix it with the colder air along the ground. Whether warm and cold air can thus be mixed sufficiently to raise the temperature throughout the orchard probably depends on the depth of the cold layer near the ground and the height of the warm air. At present this method of frost prevention is only in the experimental stage and is not to be generally recommended. Orchard Heating. — Heating is practicable in many orchards in Cali- fornia. Although somewhat expensive, and having limitations, it has become a common practice. As the temperature in the orchard can thus be raised only a few degrees, the method is limited to locations in which only light frosts occur. If a locality has frosts that damage almond blos- soms once in five years or less, it does not pay to equip the orchard for heating. If frosts occur more often, heating may be worth while when conditions are such that a reasonably heavy crop can be secured. The cost of fuel at the present price is not important if the orchard need be heated only one or two nights ; but if heating is necessary for several successive nights a financial loss may result. In one instance on record an almond orchard was heated on 17 successive nights. Although the crop was heavy, the owner lost money because of the amount of fuel oil used. Localities in which it pays to heat can be determined only by experience or from temperature records taken over several years. Among the types of fuel used have been briquettes, almond hulls, and oil. The types of heaters vary from tin cans to expensive devices (fig. 5) . As almond hulls are usually wasted, many growers have tried to utilize them in orchard heating, with various degrees of success. The dried hulls, saturated with oil, are commonly burned in a cylindrical type of heater similar to No. 17, figure 5, but larger in diameter and perforated. This sheet-iron type has the advantage over cylinders made of screen because the hulls burn more slowly. Almond hulls used for fuel are less expensive than oil but also less convenient to use. In California and other states, oil has been the most common fuel for orchard heating. Oil with a specific gravity test of 20 to 25 degrees Baume is considered best for the purpose. Probably it should be as free from impurities as possible. Formerly growers feared that sulfides or other compounds resulting from burning oil containing sulfur would 16 California Agricultural Extension Service [ Cir - 103 damage the stigmas of the blossoms and prevent the proper setting of fruit. Experiments conducted during one season by the writer, however, showed no harmful effects from burning such oil at blossoming time. The length of the period of bloom during which intermittent heating may be necessary may be two or three weeks or longer, according to the Fig. 5. — Names of some orchard heaters: 1 . Pomona. 2. Kittle. 3. Scheu Jumbo Cone Louvre. 4. Scheu Baby Cone Louvre. 5. Scheu Double Stack. 6. Bolton. 6s. Bolton (with spider). 7. Troutman. 8. Canco. 8s. Canco (with spider). 9. Dia- mond. 10. Dunn. 11a. Citrus, 9-gallon, low stack. 11b. Citrus, 9-gallon, medium stack, lie. Citrus, 9-gallon, high stack. 12a. Citrus, 6-gallon, low stack. 12b. Citrus, 6-gallon, medium stack. 12c. Citrus, 6-gallon, high stack. 13. Karr. 14. Jessen, large. 15. Jessen, medium. 16. Jessen, small. 17. Low Delivery. 18. Baby Double Stack. 19. Citrus Gas Flame. (From Bui. 442.) district, the season, and the variety. During this time accurate thermom- eters or thermostats with warning signals should be provided to notify the grower when the fires should be lighted. Crops have been lost because of inaccurate thermometers, and fuel has often been wasted because the grower has burned it before the temperature dropped to the danger point. If an orchard is to be heated, the equipment should be adequate. 6 From 75 to 100 pots of the lard-pail type to the acre is advisable. 6 Young, Floyd D. Frost and the prevention of damage by it. U. S. Dept. Agr. Farmers' Bui. 1096:1-48. 1922. Schoonover, Warren E., and F. A. Brooks. The smokiness of oil-burning orchard heaters. California Agr. Exp. Sta. Bui. 536:1-67. 1932. Almond Culture in California 17 ATMOSPHERIC HUMIDITY AND RAINFALL Too much humidity in the air during the growing and ripening season is detrimental. Foggy or damp weather is especially harmful in the spring or during the ripening period. Such weather not only prevents the proper maturing of the nuts and dehiscing of the hull, but promotes such diseases as brown rot and shot-hole fungus. Growers often ask how much rainfall will produce almonds without irrigation. The average amount of rainfall that will maintain the trees and enable them to bear regular crops depends on its annual variations, its distribution throughout the year, the time and intensity of the rains, the character of the weather following, and the ability of the soil to re- ceive and retain moisture. Where the winter rainfall has been well dis- tributed and other conditions are favorable, good almond crops have sometimes been borne without irrigation. Under most conditions, how- ever, the annual rainfall has not sufficed to produce maximum crops in old bearing orchards. In some sections it varies greatly from year to year. Often it falls so that a large proportion is lost in the surface runoff. In many places the soil cannot hold sufficient water for the requirements of the trees throughout the summer, much of the winter rainfall being lost in the underground drainage. Under some conditions, a heavy and well- distributed rainfall may suffice to produce good almond crops ; but in most districts, orchards are liable to suffer from inadequate rainfall, and irrigation is necessary or at least advisable for growing maximum crops. SOIL KEQUIREMENTS The almond, a deep-rooted tree, probably draws heavily upon the plant- food elements of the soil. Colby's analyses 7 of fruits and nuts show that the almond leads in the total quantity of mineral matter withdrawn from the soil per ton of fresh fruit. As Colby further states, "The stone fruits fall much below the almond in total ash (mineral matter) excepting the olive, the ash of which, however, is largely silica (nearly eight-tenths), an ingredient so plentifully distributed in all soils that it is of no pecuni- ary value." Colby's conclusions, based on the data in table 6, are made, however, solely by comparing the amount of each element found in each pound of fruit and do not indicate the number of pounds of fruit re- moved per acre. The amounts removed could be calculated by using these data and the acre-yield data of the different crops when available. Apri- cots, for example, remove much less of the food elements per ton of fruit than almonds do ; but the yield may be so much heavier for apricots than 7 Colby, George E. California walnuts, almonds, and chestnuts. California Agr. Exp. Sta. Rept. 1895-1897:142-159. 1898. (Out of print.) 18 California Agricultural Extension Service [Cir. 103 for almonds that actually more food elements are removed per acre. These data are given only as the best obtainable. Almonds are grown with varying degrees of success upon soils of all possible types, from the lightest sands to heavy adobe. Where other con- ditions are especially favorable, almond orchards succeed fairly well even upon soils far from ideal. The heaviest yields are obtained, however, where the soil is deep, fertile, and well drained. With poor soil, the grower is handicapped from the start. Light Soils. — Almond orchards are grown extensively upon light sandy soils and upon rolling sandy lands. Sandy loams are considered TABLE 6* Soil Ingredients Removed in 1,000 Pounds of Fresh Fruit or Nuts Fruit Almond (hulled) Almond (not hulled) . Walnut (hulled) Walnut (not hulled) . . Chestnut (hulled) .... Chestnut (not hulled) Prunes (green) Apricots (green) Olives Potash pounds 5.49 9.95 1 56 8.18 3.72 3 67 2.66 2.83 8.55 Lime pounds 1.72 1 04 1.81 1.55 0.71 1 20 0.13 0.18 2.32 Phosphoric acid pounds 4.33 2.04 2 78 1 47 1.89 1.58 0.53 0.71 1.18 Total ash pounds 15.00 17.29 7.50 12.98 8 20 9.52 4.03 5.16 94.63f Nitrogen pounds 16 40 7.01 10.20 5 41 8 00 6.40 1.48 2.29 5 85 * Colby, George E. Annual report of the California Agricultural Experiment Station 1895-1897:158. 1898. t 80.7 pounds of which is silica. favorable for almonds. Often, however, sandy soils are deficient in food material and require special attention in supplying organic matter and in keeping up their fertility. Sandy soils are easy to cultivate and do not bake on the surface, but often they are difficult to irrigate. Heavy Soils. — While the almond does well in moderately heavy soils and sometimes even on adobe, very heavy soils are not desirable. The reason is not so much the quality of the soil itself as the difficulty of maintaining a proper amount of moisture. It may be difficult, for ex- ample, to get irrigation water down through adobe, although moderately heavy soils, especially if loamy, can be irrigated satisfactorily. Heavy soils require special irrigation and cultivation and the addition of or- ganic matter. Deep-rooted plants such as alfalfa loosen such soils and aid the water to penetrate. Often the water must be run on them for a long time to insure proper penetration. Some varieties of almonds, for example the Sultana, stand heavy or adobe soils better than others and some rootstocks are better adapted to heavy soils than others. Because some of the best old orchards on heavy soils are on bitter-almond roots, Almond Culture in California 19 such stock is generally considered preferable for almonds planted on heavy soils. Depth of Soils. — Deep soils are especially favorable to the almond. In the digging of pits, cellars, and wells, almond roots have been found as deep as 12 feet ; but generally in pulling up orchard trees most of the roots have been found comparatively near the surface. Probably most of the feeding roots are within the top few feet. Deep soils are desirable be- cause they permit of extensive distribution of the roots and provide a large volume of soil to hold moisture and supply plant-food material to the trees. The soil, therefore, should be at least 6 feet deep, and probably 10 or 12 feet would be better. Substrata. — The type of substratum is of great importance. Com- pacted substrata, whether hard clay, sandstone, or calcareous layers, are undesirable, especially when near the surface ; they hinder root growth, proper drainage, and the water supply. If an impervious substratum occurs near the surface, the soil above it dries out quickly in hot weather and becomes saturated in wet weather. Such soils need frequent, careful, light irrigations. Even the best of care cannot always prevent extremes in moisture conditions, especially with old trees. Impervious layers, if comparatively thin, may well be broken up with dynamite so that the roots may grow into the soil below, especially if the deeper soil is good, llardpan should be avoided when too thick, too near the surface, or underlain with poor soil. At best, hardpan causes difficulties. Alkali Soils. — Though the almond will withstand a little alkali or other salt, there is no evidence to indicate its exact tolerance. It is prob- ably less tolerant than is generally supposed. Although most almond orchards are on slightly alkaline or neutral soil, they will not thrive if the soil contains alkali in quantity. Lands containing large amounts of alkali 8 should therefore be avoided. Organic Matter. — The presence of a good supply of organic matter in the soil is important. Besides affecting the supply of plant-food materials and aiding the growth of beneficial soil organisms, organic matter im- proves the mechanical condition of the soil and the penetration of mois- ture. As California soils commonly are deficient in humus, the addition of organic matter is usually desirable. Drainage. — Soils should be well drained. Almond roots and even peach roots are somewhat exacting in their moisture and aeration require- ments. In soils waterlogged for any considerable time the trees will suffer or even die. Often trees suffer from improper soil-moisture conditions rather than from the lack of fertility of the soil itself. A fluctuating 8 Hibbard, P. L. Alkali soils, origin, examination, and management. California Agr. Exp. Sta. Cir. 292:1-14. 1931. 20 California Agricultural Extension Service [Cir. 103 water table is detrimental to the almond, except perhaps at a depth greater than 10 feet. A rise in the water table in summer for any consid- erable period is generally believed to be injurious. Moisture in the Soil. — Because the almond tree can live from year to year under adverse moisture conditions, many erroneous opinions arose as to the possibility of growing a profitable crop where available soil moisture was lacking. The almond became known in California as a "tough" tree and was planted on a commercial scale even under desert conditions. Although many such plantings have disappeared, several thousand acres are grown today where available moisture is lacking for long periods each year. Except during wet seasons and in a few localities where the rainfall is heavy and well distributed, good almond crops can- not be expected without irrigation, even on satisfactory soils. VARIETIES The early plantings of almond trees consisted of foreign varieties intro- duced by eastern nurserymen and by the United States Department of Agriculture. Two California nurserymen, Felix Gillet of Nevada City and John Rock of Niles, as well as various growers also were responsible for several introductions. Except for a few such as the Jordan, Marcona, Tarragona, and Valencia, which were generally not adapted to Cali- fornia conditions, the introduced varieties produced poor nuts, from the marketing standpoint. Later, seedlings were grown in California, and those thought most suitable were selected. Over one hundred varieties thus originated have been grown commercially in California. Unfor- tunately the extensive plantings produced inferior nuts that competed strongly in the market with the great quantities of poor almonds im- ported from foreign countries. There was, however, a strong demand for some of the better introduced varieties, such as the Jordan, which pos- sesses a large, smooth, attractive kernel, popular with the confectionary trade. Because of its prestige, extensive attempts were made to grow the Jordan in California, but all such plantings failed. An exceedingly shy bearer, the tree does not produce a satisfactory yield in California. The nut has a very hard shell, difficult to crack, and the percentage of kernel is low in proportion to the shell. Because other foreign varieties tested in California likewise proved unprofitable, the plantings of them have practically disappeared. CHOICE OF VARIETIES One of the most important problems is a wise choice of varieties. As ex- perience has shown, the grower is limited to the varieties originated in California. These are described in detail in a United States Department Almond Culture in California 21 of Agriculture bulletin 9 from which are quoted the following paragraphs regarding certain fundamental considerations : While a few of the California varieties have proved valuable, most of them are relatively worthless, and their dissemination and cultivation have resulted in much disappointment and loss. Unsatisfactory conditions in the industry have resulted because of the failure of growers to appreciate the fact that in the choice of a variety for cultivation all of the factors relating to both production and marketing must be taken into account. None of these can be disregarded without loss to the grower. A variety is not satisfactory unless it fulfills the requirements of the grower, the dealer, and the consumer. The ideal almond variety from the producer's standpoint is one that bears regularly and well. The tree should be vigorous, hardy, reasonably resistant to diseases and to insect infestation, and of a moderately upright sym- metrical habit of growth, with a head somewhat open in the center. The blooming period should be rather long and should coincide with the period of least danger from frost in the district. Blossoms should be produced in profusion. Self -fertility of a variety would be desirable but to date no self-fertile variety has been discovered. The variety should be inter-fertile with the better commercial varieties. The nuts should be well distributed about the tree and along the branches ; they should ripen at the same time; should, when ripening, remain attached to the tree with sufficient tenacity to prevent dropping during ordinary winds, but not be so firmly attached as to make harvesting difficult ; dehiscence of the hulls should be complete enough to make hulling easy, and there should be no "sticktights." The nuts, like the tree, should also be reasonably resistant to insect attacks and diseases. Some of the requirements of the dealer and consumer are as follows: The nuts should be attractive and uniform in appearance, with a bright-colored, soft, smooth, well-sealed shell, easy to crack, and yet free from a spongy or crumbly shell. The kernels should be single, plump, large, attractive in shape, free from pubescence, with a good flavor, and preferably with sufficient oil content to satisfy all branches of the confectionary trade. When the necessity of taking all of these requirements into account is realized, it is not difficult to see why most of the varieties grown in California, whether native in origin or imported, have proved unsatisfactory. In many instances varieties have been widely advertised and extensively planted because they possessed one or at most a few of the desirable qualities, such as a heavy bearing tendency, a thin shell, or an attractive appearance. The fact that they possessed defects so marked as to render them practically worthless was overlooked. It is not strange that under these circumstances many orchards were operated at a loss. Inferior nuts can be disposed of profitably only during periods of abnormal demand. In normal or depressed times the market for such nuts disappears, and they can be disposed of only with great difficulty, if at all. At best, they bring prices which do not give adequate returns to the grower. No existing variety is satisfactory in all respects ; but, until better varieties can be originated 10 the grower must manage as well as he can. 9 Wood, Milo N. Almond varieties in the United States. U. S. Dept. Agr. Dept. Bui. 1282:1-141. 1925. (Out of print.) 10 A breeding project is being conducted cooperatively by the U. S. Department of Agriculture and the University of California. Although some of the new originations possess outstanding merits, several years of trial will be necessary before they are grown commercially. 22 California Agricultural Extension Service [Cm. 103 Among the most important and valuable varieties are the Nonpareil, I. X. L., and Ne Plus Ultra, which are often known as the Hatch varieties because they were originated by A. T. Hatch of Suisun, California. Other varieties now grown extensively are the Drake, Texas, Peerless, Lewell- ing, and Languedoc. Although a small acreage of the Eureka has been planted, the number of trees now in bearing is limited. The production of inferior varieties has decreased greatly, and now amounts to only about 5 per cent of the total tonnage. This reduction in production of inferior quality nuts has helped solve the earlier problem of marketing nuts that compete on an unfavorable basis with foreign importations of the same class. THE RELATION OF VARIETIES TO THE MARKET AND TO THE GROWER Obviously the demand for nuts depends upon their uses. Though the quantity needed for particular purposes varies from year to year, the several uses remain rather stable. As yet no one variety can satisfy all trade demands; the market requirements are for several types of almonds. The grower derives most profit from the varieties that are adapted to particular trade requirements while presenting the fewest or least serious problems of production. In the United States, almonds have long been sold in the shell to the consumer, especially during the winter holiday season. For this purpose the appearance of the shell is important, and often the qualities of the kernel have been neglected. The so-called "soft shell" varieties are most in demand for sale in the shell, such as the Nonpareil, I. X. L., Ne Plus Ultra, Drake, and Peerless. The Nonpareil often presents a rather poor appearance but has a very soft shell, a smooth, light-colored, and shapely kernel, and the nut is easily cracked with the fingers. The I. X. L. is pop- ular because of its large, bright, smooth shell free from blemishes, and its well-shaped, high-quality kernel ; but the kernel is frequently gummy. The Ne Plus Ultra has large size and a fine-appearing shell, but the kernel is rough, pubescent, and also subject to gumminess. The Drake, being fairly large, with a reasonably attractive shell and a good-flavored kernel has become popular in many markets, competing with the im- ported Tarragona. Unfortunately it tends to produce double kernels. The Peerless is popular in certain markets because of its large size and handsome shell. The shell is so hard and thick, however, that the kernel constitutes a relatively small proportion of the nut. The demand for the Peerless is fairly good in most years. Recently the year-round market for nuts has improved, and the holiday demand is less in proportion to the annual consumption than formerly. The proportion of shelled nuts used has also increased tre- Almond Culture in California 23 niendously. At present, probably not more than 50 per cent of the total quantity of almonds reaches the consumer in the shell. When almonds are sold as kernels, the cracking- qualities of the nut and the appearance and quality of the kernel are the most important considerations. THE UTILIZATION OF ALMOND KERNELS AS AFFECTING DEMAND FOR VARIETIES The use of almond kernels in specially prepared or manufactured forms bears an important relation to the demand for certain varieties. Below are given some of the more important uses and the varieties most desired in each case. Blanched Salted Almonds- -Blanching is one of the oldest and most widely known processes used in the preparation of the nuts for consump- tion. The pellicle or "skin" of the kernel is first removed. The nuts are then cooked in an oil bath or roasted slightly, and salted. Almonds thus prepared make a very fine food product. There is great variation in the suitability of varieties. The imported Marcona is in great demand for blanching and in some markets brings a premium price. Most processors consider the Nonpareil kernel as somewhat inferior to the Marcona for this purpose. The Nonpareil kernel must be dried to a certain moisture content if the product is to be crisp. Of the California varieties the Drake is well liked for blanching and salting because of its excellent flavor. Its double kernels are its chief objection. The blanching, salting, and roasting of almonds is discussed in a manual by the California Almond Growers' Exchange. 11 Roasted Almonds. — In roasting almonds, the kernels are not blanched, but are roasted in the pellicle or skin without salting. Roasted almonds are used in ice cream, chocolate preparations, and confectionary prod- ucts. Nonpareil, Drake, Texas, and Ne Plus Ultra kernels are much used for this purpose. Toasted Almonds. — Kernels roasted and salted are called toasted al- monds. As with the roasted product, the pellicle is not removed. Toasted almonds are used in the same way as salted almonds, and the demand is considerable. The Nonpareil, Drake, Texas, and several other varieties have been used for this purpose. Almond Paste. — Almond paste, one of the oldest and best known of almond products, is made of blanched kernels which are ground, cooked, mixed with sugar and water, and sometimes with oil of bitter almonds and various flavoring materials. No satisfactory substitute has been 11 California Almond Growers' Exchange. Manual of special instructions for large-scale blanching, salting, roasting, and toasting of California almonds. 30 p. California Almond Growers' Exchange, San Francisco, Calif. 24 California Agricultural Extension Service [ Cir - l° 3 found for almond paste in the baking trade, especially in the making of macaroons. Many firms have their own special methods of preparing almond paste, and some have built up valuable reputations for their products. The paste is often marketed in sealed tins to housewives as well as to the large bakeries and confectionaries. Frequently the cheaper va- rieties of almond kernels are used in order to keep the cost of the paste as low as possible, although nuts with a good oil content are preferred. A variety that lacks oil may be mixed with some variety with a high oil content, or almond oil may be added. Almond Powder. — In making almond powder, the kernels are blanched, ground, and mixed with sugar but not cooked. The powder keeps readily in cans or paper cartons. Its convenient, usable form appeals to the housewife. Almond Butter. — Almond butter consists of ground roasted almond kernels to which salt is added. A high-quality product, it will keep a long time in vacuum-sealed glasses or cans. Because it costs more to produce than does peanut butter, with which it must compete, the market is lim- ited to a discriminating trade. The low-priced varieties are often used for this purpose in order to lessen the cost of manufacture. Almond Confection. — For almond confection the kernels are ground after roasting and mixed with sugar ; often a little salt is added. Before use, the confection is made into a paste with water or almond oil. Sugared Almonds. — Raw almond kernels are blanched, sometimes roasted slightly, soaked for a short time in sirup, and then dried rapidly. The resultant sugared almonds appeal to many persons. Although this use is not common, it may be developed further. Almond Oil. — Oil of both bitter and sweet almonds is used in large quantities. It is usually a foreign product — especially the oil of bitter almonds ; California almonds are not yet used to any great extent for this purpose. Cosmetic and Pharmaceutical Preparations. — From early times the almond has been widely used in medicines and cosmetics. At present more almonds are used in cosmetics than is generally realized. Oil of almonds, almond meal, and other forms are extensively employed in the manufacture of almond soap, face creams, and perfumes. GROUPS OF VARIETIES FROM THE MARKETING STANDPOINT California commercial almond varieties may be classified according to their use in satisfying the various market requirements. Varieties marketed both shelled and unshelled are sometimes called dual-purpose nuts. The highest-priced nuts such as the Nonpareil, Almond Culture in California 25 I. X. L., and Ne Plus Ultra are in this group. The Drake is also well liked because it blanches well. These varieties were the most important in establishing the California almond industry. Varieties suitable for sale in the shell only are the Peerless, Bidwell, Garwood, Almendro de la P, and others whose shell is handsome in size and color. These nuts are hard-shelled, and usually the kernels possess some objectionable features. Because of the small percentage of kernel to the shell, they cannot be sold profitably in kernel form. The market for this type of nut is not so important as formerly, because of the in- creased demand for almond kernels. The Peerless has been the outstand- ing variety in this class and has sold rather successfully. Any large increase in production of the Peerless, however, might easily result in an oversupply. Among the varieties marketed almost entirely as kernels are the Texas, Languedoc, Lewelling, and others. The increasing demand for such nuts has built up an extensive trade in these varieties. During the past few years there has been an increasing demand for small kernels. About 50 per cent of the domestic and nearly all the imported almonds used in our country are retailed as kernels or in manufactured products. Nuts of the Texas type are not suited to blanching because of the difficulty of removing the skin of the kernel. Among the varieties which show some promise, but for which the mar- kets are limited, or which can be grown profitably only in certain locali- ties and should be planted cautiously are the Eureka, Batham, Ballard, Long I. X. L., and a few others. Varieties possessing good qualities from the consumers' standpoint, but not grown profitably in California because of the cost or difficulty of production include the Jordan, Marcona, Klondike, and Princess. VARIETIES RECOMMENDED FOR PLANTING IN CALIFORNIA Though no variety is ideal, the grower should plant those best suited to the market and the locality. The following are among the best : Nonpareil. — The Nonpareil, generally considered the best all-around California variety, is a good nut from the marketing standpoint, both for sale in the shell and as kernels. It bears fairly regularly and seems adapted to practically all the almond-growing districts in California. It has not, however, yielded so well as some other varieties in a few localities where water has been lacking. Because of its paper shell, the percentage of kernel to the nut is high. It has led all the varieties as to price. The tendency to establish prices on a kernel basis — that is, the proportion of kernel to shell — keeps the variety in the top price class. Though it does 26 California Agricultural Extension Service [Cm. 103 not bear such heavy crops as some others, its regularity of bearing and its high price have made it one of the most profitable nuts for most orchards (fig. 6). I. X. L. — The I. X. L. is a desirable nut from the marketing stand- point. In shape the kernel somewhat resembles that of the Mareona. The growers, however, find the I. X. L. a light bearer and often unprofitable. Fig. 6. — Some common almond varieties. Beginning at the upper left they are : Languedoc, Nonpareil, Tarragona, Texas, I. X. L., Jordan, Drake, Ne Plus Ultra, and Peerless. (From Bui. 297.) Apparently it produces best in the foothill districts and in a few favored valley locations. It is rather exacting as to its cultural requirements ; the kernels are often subject to gumminess ; and the variety is intersterile with the Nonpareil. It should be planted extensively only where already profitable (fig. 6). Ne Plus Ultra. — Ne Plus Ultra became popular partly because of its value as a pollinizer for the Nonpareil. The attractive shell and large size of the nut and kernel built up a market for it. The kernel approaches the Jordan in shape, but is less highly rated in the market. In many respects the Ne Plus Ultra is even more particular in its requirements than the I. X. L. The size of the nut and the plumpness of the kernel are greatly Almond Culture in California 27 affected by the supply of soil moisture. The kernel is often defective when moisture is lacking, and the nuts frequently are gummy when the soil becomes even slightly waterlogged. Often gumminess takes place even under the best environmental conditions. Both the nuts and the tree may be injured by shot-hole fungus, especially when weather con- ditions encourage infection by the fungus before the shell of the nut is Fig. 7. — Some common almond varieties. Beginning at the upper left they are: Harriott, King, Stuart, Eureka, California, La Prima, Lewelling, Princess, and Batham. (From Bui. 297.) formed. Because of its limitations care should be taken in selecting the Ne Plus Ultra for extensive plantings (fig. 6). Drake. — Although the Drake fills a certain place in the market and is widely planted in California, it is less profitable than has been generally supposed. The tree is scraggly and spreading, and difficult to train to shape. It has a marked tendency toward alternate bearing, producing a heavy crop one year and a light one the next. It is subject to attack by disease. With the exception of the Gordon, the Drake is the variety most susceptible to brown rot, which is increasing in prevalence. When planted mainly as pollinizers for other varieties, the Drake trees can be kept down to a minimum number (fig. 6) . 28 California Agricultural Extension Service [Cir. 103 Texas. — The Texas was once considered rather worthless because the small nut presented a poor appearance. With the increasing demand for almond kernels and the perfection of cracking machinery, however, the variety has become outstanding, the only question being whether the demand for small kernels of the Texas type will be permanent. The nuts are rather undesirable for blanching because the pellicle of the kernel is difficult to remove and the slightly bitter flavor of the kernel is objec- tionable to many. Their sale, accordingly, is limited to particular chan- nels. From the growers' standpoint the variety has many desirable quali- ties. It blooms late and frequently escapes frost when the earlier varieties are damaged. In most localities it yields regularly and well. Its main fault is that the nuts ripen late and in some districts are occasionally caught by early fall rains (fig. 6) . Peerless. — Although there is considerable demand for the Peerless, extensive plantings would probably result in an oversupply. The nuts knock and hull easily ; but when ripening, they drop so easily that winds may scatter them, making it necessary to harvest them very early or to pick them from the ground, an expensive and annoying process. While blossoming, the variety is especially subject to frost injury. Slight frosts that may not harm the blossoms of other varieties often damage the Peer- less. Apparently the variety has thrived in the Winters and Chico dis- tricts. It seems to do best on rich deep soils. Because of its thick, heavy shell, a given quantity of nuts is heavy, and in suitable districts the yield is often high. The percentage of weight of the kernels, however, is very small. If sold on a kernel basis, the nuts would not prove profitable even under the best conditions. The Peerless is of value as a pollinizer for the Nonpareil. It should be grown only in sections where it yields especially well (fig. 6). Eureka. — Apparently the Eureka tree withstands adverse conditions, such as shortage of water and poor soils, better than most varieties. Be- cause of the small size of the nut, many growers claim that the cost of harvesting is proportionately high. While there is some demand for it at present the Eureka should be planted sparingly (fig. 7). The grower is rather limited as to choice of varieties. Ordinarily he should plant heavily of the Nonpareil, and in suitable districts he should plant some I. X. L. A few trees of the Ne Plus Ultra and other varieties just discussed would complete the orchard. In the few localities not suited to the Nonpareil, the grower must select other varieties. In any case, suitable pollinizers must be provided. Almond Culture in California 29 POLLINATION Pollination must take place before almond blossoms can set fruit. No almond variety will produce nuts in commercial quantities when self- pollinated. Almond varieties, therefore, are said to be self -sterile or self- unfruitful. Each must be cross-pollinated with another variety. A few varieties are intersterile, and will not pollinate each other — for example, Texas and Languedoc, and Nonpareil and I. X. L. A problem in pollen distribution therefore arises. Distribution of Pollen. — Almond flowers are adapted to insect pollina- tion. When bees and other insects visit almond blossoms, the pollen adheres to their bodies and is carried from blossom to blossom and from tree to tree. The grower can arrange for proper pollen distribution by providing a suitable mixture of cross-fertile varieties and an ade- quate number of bees. The number of hives of bees that should be placed in the orchard depends upon the size of the trees, the length of the blos- soming season, the weather, and the number of bees to the hive. If the flowering period is long, with abundant sunshine and little wind, one hive would probably serve several acres. Cold, wind, or rain, on the other hand, prevent bees from working, and when such weather prevails dur- ing this period, a large number of bees may be required to pollinate the orchard adequately. In general, one hive per acre is considered ample, even in adverse years. Most almond growers find it inconvenient to keep bees and a beekeeper is usually hired to move his colonies into the orchard during the blossoming period. He is commonly paid a certain amount per hive and also gets the honey made from the almond blossoms, which is bitter and can be sold only to the confectionary trade. For more details in regard to bees and pollination the reader is referred to Extension Cir- cular 62. 12 There seems to be much misunderstanding regarding the relation of wind to pollination. Although wind is important in transferring pollen of the so-called "wind-pollinated" plants such as the walnut, chestnut, pecan, pistachio, and filbert, it is of only minor importance in the almond. The writer's experiments showed that strong winds carried considerable almond pollen from row to row. In a few instances pollen grains were carried as far as 60 feet ; but being rather heavy, they generally dropped rather abruptly. At considerable distances, very little pollination was accomplished. In nearby trees, sometimes 5 to 10 per cent of the blossoms were pollinated by strong winds. Although wind-pollination sometimes produces light crops, and is helpful in special instances, it is usually 12 Philp, Guy L., and G. H. Vansell. Pollination of deciduous fruits by bees. California Agr. Ext. Cir. 62:1-27. 1932. 30 California Agricultural Extension Service [ Cir - 103 insufficient to cause the setting of commercial crops. In many cases wild bees and other insects have caused the setting of almond crops attributed to wind-pollination where hives of bees were not present. Factors Necessary to Insure Pollination. — Almond varieties are self- sterile and, therefore, more than one variety must be planted in the orchard. Except such intersterile varieties as the Nonpareil and I. X. L., or the Texas and Languedoc, any variety will pollinate any other one, provided the flowering periods are nearly the same so that the pollen of ■m®£k 'ii • 4< I > r *"; *-\y « "" E F ° Fig. 8. — Variation in time of blossoming of seven almond varieties. Note the varieties in bloom, that will pollinate one another. The early varieties are now in full foliage. From left to right : A, I. X. L. ; B, Languedoc ; C, Lewelling ; D, No Plus Ultra ; E, Texas ; F, Reams ; and G, King. Characteristic growth habits of these varieties are also shown. one variety is produced while the pistils of the other are receptive. In other words, to insure cross-pollination one must plant interfertile varie- ties that bloom at about the same time. Blossoming habits vary with the variety, location, soil and soil mois- ture, season, and climatic factors. Good pollinizers should produce viable pollen in profusion and have a rather long flowering period. Although the season, climate, and other factors have a great influence, some varie- ties tend to produce more bloom than others. The Sultana, for example, produces only a few scattering blossoms. Though a variety having light bloom may set enough fruit, it cannot be considered useful for pollina- tion. The Bidwell, Princess, and I. X. L. tend to produce rather scant bloom, whereas the Harriott, Ne Plus Ultra, Lewelling, Long I. X. L., Bigelow, Walton, Trembath, Texas, and Reams usually have an abun- dance of blossoms. The relative time of bloom is primarily a varietal characteristic. Though the season and climate exert a marked influence, varieties in an orchard or in a locality tend to bloom in approximately the same order year after year (fig. 8) . Within a given variety, young trees bloom later than old, the difference in time varying from a few days to as much as Almond Culture in California 31 three weeks. One must consider this variation when determining what varieties to plant together for pollination. Only trees of the same ag'e can be compared exactly. For this reason and because of climatic, soil, and soil-moisture effects, varieties blossoming at nearly the same time may Fig. 9. — Chart showing order of blossoming of almond varieties. The earliest variety is the Harriott to the left of the letter A. Follow- ing the direction of the arrows the varieties bloom in succession until the Sultana is reached, which is the latest flowering variety given. The lines originating at A, B, C, D, and E drawn from the inner to the outer circles divide the varieties into groups which bloom close enough together to pollinate one another, even in the most unfavor- able seasons. The dotted lines drawn from the center of the figure to the inner circle, dividing the circle into segments 1, 2, and 3, sepa- rate the varieties into groups, any variety of which will pollinate an- other variety in the group during the best of seasons — that is, when the bloom of all varieties comes close together. The heavy arcs drawn within the inner circle indicate the varieties which pollinate one another in the average season in the average locality. not always follow the same sequence. Ordinarily, for example, Ne Plus Ultra blooms slightly earlier than I. X. L. ; but sometimes the reverse is true. Though varieties may bloom near enough together to insure cross- pollination in a single season, one must take blossoming records over several years before deciding what varieties to plant together for inter- pollination. 32 California Agricultural Extension Service [Cir. 103 In California, almonds bloom from the last of January to the last of March or early April. The order of blooming of 44 varieties is shown in figure 9, from which the varieties that bloom at a proper time to pollinate each other can be determined. The average blossoming period of 21 almond varieties for several years at the University Farm, Davis, California, is shown in figure 10. In data collected over a series of years to show averages, however, the periods of coincidence of bloom of different varieties is often srreater FEBRUARY MARCH YEARS averaged Harriott 8 Ne Plus Ultra . . 8 Big White Flat. 7 I.X.L 8 Eureka 1 California 8 King 8 Klondike 7 Jordan 8 Lewelling 8 Peerless 8 Princess 8 Nonpareil 8 Drake 8 Silver Shell ... 7 Dickinson 3 Golden State ... 7 Languedoc 8 Texas 8 Sellers 7 Reams 8 Fig. 10. — Average blossoming dates of certain almond varieties at Davis, Cali- fornia, 1914 to 1921 inclusive. The beginning of full bloom in each case is indicated by F. (From Bui. 346.) than it is during individual years. If varieties are selected according to the average date of bloom, mistakes may be made. It is better, there- fore, to select varieties for pollinating purposes from yearly records, one of which is given in figure 11. To illustrate : according to the average blossoming dates in figure 10, even the Harriott and Reams, or Ne Plus Ultra and Reams would pollinate each other. In reality this would happen only in extreme years. The facts are more nearly represented in figure 11. As figure 9 shows, for any variety selected for planting, several polli- nating varieties can be had. The difficulty lies in obtaining for pollination purposes varieties that stand high commercially. New varieties are there- fore needed. fl io \? 14 ifi fl ?(i n M n ?f 2i 4 a 18 hoi iz lu ife la tc ?2 14 mm KBC -1 Almond Culture in California 33 Seasons have a marked effect on the relative time of bloom. When a cold dormant period is followed by a warm, sunny blossoming season, early and late varieties bloom somewhat close together. In districts hav- ing such seasons the Qrake or even the Texas pollinates the Nonpareil. Such seasons are especially marked in St. George County, Utah, which has few pollination troubles even when early and late-blossoming varie- ties are grown together. In most years, certain sections of the interior Period of Effective Klojjcn\ina of Ahnoitclj- University Yzxxi\~\ c lY]. FEBRUARY Harriott NePluj Ultra I.X.L Peerlej./ Jordan Princes j Jewelling California. King Nonpareil Golden Jfcvte brake Lang ue doc Texa ¥'' ' V'.-" ! ' r '"■' ! " m w '> V £>3i)j|j ' . /, f \ / 1 ■ l it HI rf is f f *H ilB^iips BBPil*.' & m ^*~** ;J3 • ' ' -V . , V-_ •..■'• " -' : '* - : < r i [ : - ■ Fig. 14. — Almond tree on almond root. This particular root has been very vigorous and has grown faster than the top. Though the best unions are generally believed to be smooth, with scion and stock of nearly the same diameter, this orchard, now sixty-five years old, is still bearing well. The diameter of the stock at the ground is 36 inches. ous, and have better foliage than those on peach roots ; they also produce fewer sticktights. The almond root tends to grow deeper than the peach and probably withstands drying out of the soil at the immediate surface better. Although somewhat sensitive to fluctuations of the water table near the surface, it responds readily to proper moisture conditions and also withstands drought better than any of the other stocks mentioned. It makes good growth on limestone soils and the trees in such soils are thrifty. One must remember, however, that there are all kinds of almond roots, according to the kind of seed from which the roots are grown. Often mixed types of seed have been planted, and the resulting trees Almond Culture in California 39 budded to the desired varieties regardless of the vigor of the stock. In some eases only the thrifty, vigorous stock is used, the rest being de- stroyed. This is apparently the best practice. The bitter-almond stock is often recommended as superior to the sweet almond. Experiments indicate that there is as much variation among the bitter-almond stocks grown from seed from different trees as among Fig. 15. — Method of cleft grafting commonly used in top-working almonds. the seedlings from sweet almonds. It was once believed that rodents would not eat the roots grown from bitter seed ; in reality, both bitter- and sweet-almond stocks are attacked by gophers. Many growers still prefer bitter stock, and, though definite proof is lacking, there may be some truth in the supposition that it is the best of all stocks. The stock must be carefully selected because of the variation in rootstocks grown from miscellaneous seed. Probably a satisfactory stock can be selected from either the sweet or the bitter almond (fig. 14). The methods used in rootstock selection are mostly the result of theory, as, unfortunately, experimentation has not yet proceeded far enough to yield dependable information on the various factors that affect rootstock habits. 40 California Agricultural Extension Service [Cir. 103 PROPAGATION AND TOP-WORKING Almond trees when grown from seed will not reproduce true to variety and are therefore propagated by budding desirable varieties on seedling roots according to the usual nursery practice for the peach and other stone fruits. Generally the grower purchases the nursery trees instead of raising them, because trees can usually be grown more cheaply by a nurseryman, and there is a saving in the time required for the trees to come into bearing. Those interested in the details of propagating their own trees should consult the publications cited in the footnote. 13 Top-working is commonly performed for the purpose of changing trees of undesirable varieties to more desirable ones. The general practice is to cleft-graft or bark-graft the large branches at a convenient height from the ground, using one, two, or more scions according to the size of the branch (fig. 15). By cutting back the branches one may force out suckers that can be budded. ESTABLISHING THE ORCHARD The main steps in establishing an almond orchard include choosing and grading the land, installing the irrigation and drainage systems, laying- out the orchard, selecting the trees, planting, and caring for the young trees. Importance of Selecting a Suitable Site. — The success of a commer- cial almond orchard will be largely determined by the selection of the land with reference to frosts, soil, irrigation facilities, and drainage con- ditions. These and other important factors are discussed elsewhere in this publication. Grading the Land. — Where irrigation is to be practiced, the land should be graded before the trees are planted. Properly graded land saves much in time and expense of irrigating. The type of grading will depend upon the irrigation system to be used and upon the type of soil ; this will be discussed further in the section on irrigation. The expense of grading depends largely upon the amount of soil to be moved and the ease with which the work may be done. Installing the Irrigation and Drainage Systems. — The irrigation sys- tem should be installed before the trees are planted. As the importance of irrigation for almonds was unfortunately not realized until lately, the installation of irrigation systems in established orchards may involve 13 Hansen, C. J., and E. E. Eggers. Propagation of fruit plants. California Agr. Ext. Cir. 96:1-52. 1936. Eeed, C. A. Nut tree propagation. U. S. Dept. Agr. Farmers' Bui. 1501:1-46. 1926. Almond Culture in California 41 difficulties. The different systems and methods of installation are dis- cussed in connection with irrigation. In establishing an orchard one should insure proper drainage as well as proper irrigation. Almonds should not be planted under poor drain- age conditions. Commonly, open ditches are used; but in some cases pipe or tile are advantageous. Many almond orchards are on well-drained soils needing no special provision for drainage. Laying Out the Orchard. — Although most of the almond orchards in California are planted on the square system, in some cases the hexagonal (equilateral triangle) or the quincunx system has been used. The or- chard may be staked for each tree, or only the base lines may be staked and the trees located by means of a steel tape or marked wire. In the latter case the trees are planted directly in the proper place without previously staking for each tree. The different ways of laying out the orchard and the different planting systems are explained in the publi- cations cited in the footnote. 14 Selecting the Nursery Trees. — The grower should purchase the nurs- ery trees from reputable individuals, who are certain that the varie- ties are true to name. If possible the trees should be selected in the nursery, choosing those which are vigorous and stocky with a good root system, and which are free from disease. It pays to select them on the ground if possible. This initial investment is only a small part of the cost of establishing an orchard and bringing it into production, and any saving made by planting inferior trees will probably prove to be an expensive mistake. In California, inspection by the local agricultural commissioners insures the grower against planting diseased almond trees. Planting the Trees. — In California the planting is usually done in January and February, although sometimes not until March. The roots of the young trees should not be allowed to become dry between the time they are dug in the nursery and planted in the orchard. When received from the nursery they may be "heeled-in" — that is, the roots of the bundles may be placed in trenches and covered with soil until planted. The almond trees may well be set out in the orchard early in the winter whenever the weather permits. To secure a uniform and vigorous stand of trees, care in preparing the ground and in setting out the trees is essential. The holes should be dug- deep and wide enough to accommodate the roots. Extra long roots may be shortened, interfering and cross roots cut out, and broken or dam- u Wickson, E. J. California fruits and how to grow them. 10th ed. p. 85-92. Pacific Rural Press. 1926. Coe, Francis M. Planning, planting and caring for the young orchard. Utah Agr. Exp. Sta. Cir. 83:1-32. 1930. 42 California Agricultural Extension Service [Cir. 103 aged roots trimmed. It is important to get the soil well firmed around the roots, either by packing it there while planting the tree, or by run- ning on water soon after planting. Almond trees should be set at the same depth they grew in the nursery. Sometimes they have died because the nursery trees were planted too deep, especially in heavy soils. Planting Distances. — One of the most perplexing problems is what distance apart to plant the trees. The grower should plant as many trees per acre as possible in order to secure the earliest maximum yield but at the same time have them far enough apart to avoid a reduction in the maximum yield per tree when they become old. The optimum planting distance depends on the variety, the nature and fertility of the soil, irrigation, and the cultural practices. As far as the top is concerned, upright trees such as the Texas, Languedoc, and Klondike can be planted closer together than wide-spreading trees such as the Drake, while the Nonpareil is intermediate in its spreading habit. Trees on rich, deep soils grow larger in a given time than similar trees upon poor soils; therefore, on rich soils fewer trees should be planted per acre. In poor, shallow soils, or in soils deficient in moisture, the trees should not always be spaced with regard only to the tops and sunlight. Under such condi- tions, especially if soil moisture is lacking, the roots may need consider- able more space than the tops ; and if the trees are planted close, they may exhaust the soil moisture before the season is over. The planting distance used should assure plenty of sunlight. If planted too close, old trees grow too high towards the light, which is available only from above. Such trees, if properly pruned, have a greater tend- ency to send out numerous water sprouts than trees whose tops have room to expand laterally. After the tops interlock and shut out the sun- light from the lower portions, the smaller branches and fruit spurs in these parts gradually weaken and die, and eventually most of the crop is produced in the tops, where sunlight is available. The excessive up- right growth of the trees with the fruit production forced to the top not only increases the cost of harvesting, pruning, and spraying, but re- duces the possible bearing surface. Planting distances cannot be stated arbitrarily, because of varying conditions. Those most suitable for young bearing trees are not satis- factory for old ones. Planting distances in the older orchards vary from 16 to 35 feet, the majority of trees being set 25 feet apart on the square. In many of the newer orchards trees are 24 or 26 feet apart. On good, rich soils where irrigation is practiced, the young almond trees may wisely be set twice as close together as the permanent trees will be. Be- cause of the large number of trees, this method increases the production Almond Culture in California 43 per acre while the orchard is young. By the time the trees are so large that some must be removed, considerably more nuts will have been pro- duced than would otherwise have been the case. A young orchard planted in this manner is usually profitable, whereas if the trees are widely spaced, loss results during the first few years. Furthermore, the perma- nent trees can be spaced sufficiently to allow ample room when they are old without losing the use of the ground while they are young. When the trees begin to crowd each other, alternate diagonal rows are taken out. This plan removes the same proportion of each variety, if the varieties are planted in single rows ; and growers are well satisfied with it. Trees are now being planted 15 feet apart, making the permanent trees 30 feet apart on the square. Sometimes the trees are planted 14 or 16 feet apart. The plan is open to the objection that growers sometimes fail to pull out the filler trees when they begin crowding. Trees are removed with less difficulty, however, when the spacing of both the temporary and the permanent trees is planned for than when the distances are too great for young trees and too small for the old trees. The number of trees per acre planted at various distances under the square system is as follows : Feet between Trees per Feet between Trees per trees acre trees acre 15 193 29 51 16 170 30 48 17 151 31 45 18 134 32 42 19 120 33 40 20 109 34 38 21 99 35 35 22 90 36 33 23 82 37 31 24 75 38 30 25 70 39 28 26 64 40 27 27 60 50 17 28 55 60 12 Inter planting. — Orchard trees that require several years to come into commercial bearing are often interplanted with different types of fruit trees that will bear sooner. Thus some income is derived from the tem- porary early-bearing fillers before the permanent trees mature. The almond begins to bear fairly early and little is gained by such inter- planting. Some orchardists have followed the plan in order to find out whether the almond or some other fruit was the more profitable. Almonds have been interplanted with peaches, apricots, plums, prunes, walnuts, chestnuts, and even citrus trees. Such plantings are not recommended. 44 California Agricultural Extension Service [Cir. 103 It is difficult to irrigate and keep the soil moisture correct for two types of trees. The almond generally does well with less irrigation than most of the other orchard trees ; and either the interplanted trees suffer, or the almonds develop troubles from too frequent irrigation. Almonds and citrus trees interplanted are especially bad in this regard. Probably the peach comes nearest to giving satisfaction, but there may be practical difficulties involved in applying water, especially near harvest time. To increase the income from the young almond orchard it is better to plant the trees closer together; that is, the interplants should be almonds rather than other fruits. Caring for the Young Trees. — Before the young trees come into bear- ing they should be properly trained and pruned to form a suitable head and establish a good bearing surface according to methods discussed in connection with pruning. They should be irrigated so that they do not lack soil moisture. Usually clean culture is practiced to keep down weeds. The young trees should be protected from sunburn and injury. Borers may cause considerable trouble if the bark is killed by sunburn ; but usually the young twigs and foilage will supply sufficient shade. Some- times tree protectors are used, but young trunks thus protected become tender. If installed, the protectors should be left on all summer. Coating the trunks with whitewash is one of the easiest and most successful ways of preventing sunburn, especially if twigs are also grown to furnish shade. Because of numerous inquiries regarding the making of white- wash, the following formulas are given : 1. Slake 40 pounds of lime in boiling water. Strain, and to the liquid add 15 pounds of salt previously dissolved in warm water. Add 3 pounds of ground rice boiled to a thin paste ; stir it in while hot. Add % pound of Spanish whiting and 1 pound of glue (dissolved by soaking in cold water and then warmed over a slow fire) . To this mixture add 5 gallons of hot water. Stir well and let stand for a few days before using. Apply hot. 2. Slake 5 pounds of quicklime. While the lime is slaking add V2 pound salt and % pound sulfur. Allow the whitewash to stand several days before using. Dilute to the consistency of paint, and apply with a brush. 3. Six pounds of whiting, 1 pound of casein spreader and water to make the mixture the consistency of paint. To this add V3 P m t of raw linseed oil. When painted on tree trunks this preparation is very lasting. Sometimes spraying is necessary to protect the young trees from in- sects and diseases, as described in another section. Ordinarily, however, young trees will not need much spraying except in localities badly in- fested with insects and diseases. Almond Culture in California 45 ORCHARD OPERATIONS Though treatments of established orchards necessarily differ somewhat because of variations in soils, climate, and other factors, certain princi- ples are always applicable. A description of the best procedure in almond orchards should be of some value to experienced growers and of especial value to prospective ones. CULTIVATION Methods of cultivation for almond orchards are in general those in use for other orchard fruits. In many cases cultivation has been neglected or done carelessly because of the widespread belief that the almond with- stands mistreatment and needs less attention than other orchard trees. Nothing could be further from the truth. Although almond trees will often continue to live, profitable crops cannot be obtained under adverse treatment. Veihmeyer and Hendrickson 15 note that a certain amount of cultiva- tion is required in orchards, but that all such operations should have some definite purpose. They list the following objects of cultivation, which apply to the almond as well as to other orchard trees : "To remove noxious weeds and weed competition ; to facilitate subsequent orchard operations, such as irrigation, harvesting, brush removal, and spraying ; to incorporate covercrops and manures ; to prepare the soil as a seed bed for covercrops ; to facilitate the control of certain pests ; and to aid in the absorption of water where tillage or other orchard operations have produced an impervious condition of the soil." Cultivation in almond orchards has often been carried to the extreme. In cases where it is neglected, weeds deplete the soil moisture to the detri- ment of the trees, especially when irrigation is not practiced. In instances where cultivation is overdone, it apparently burns out the humus or organic matter, and thus injures the physical structure of the soil. Con- tinued cultivation at the same depth in some soil types may cause plow sole, which usually interferes with the penetration of the water. The results given in the publication just cited indicate that under most California conditions, comparatively little moisture is lost through direct evaporation from the soil surface ; the greatest loss is by trans- piration through the leaves of trees and weeds. According to these work- ers, cultivation to destroy weeds is important, but cultivation solely to form a mulch on the soil surface (which has up to this time been thought 15 Veihmeyer, F. J., and A. H. Hendrickson. Essentials of irrigation and cultivation of orchards. California Agr. Ext. Cir. 50:1-24. Eevised 1936. 46 California Agricultural Extension Service [Cir. 103 to prevent evaporation of the soil moisture) is of little or no value. Con- sequently, when the land has been plowed and brought to a good state of tilth, little or no cultivation will be needed through the remainder of the summer, except to kill weeds and to leave the soil in such condition that furrows or ridges can easily be made if another irrigation is neces- sary. Cultivation too soon after the soil is put in good condition not only may be a useless expense, but may lower the humus content of the soil as previously mentioned. The number and types of cultivations required vary with the soils, season, irrigation practices, size of trees, slope of land, depth of soil, and other factors ; no hard and fast rule can be given. The usual method of soil management in almond orchards is as fol- lows : The orchard is plowed or disked in the spring. Plowing varies from 4 to 8 inches in depth, but is often less. After plowing, the soil may be harrowed. Its type and condition will determine whether one should harrow or possibly roll in order to firm it and break up clods. Subsequent cultivations are according to weed growth. If there is a covercrop, care must be taken, especially where irrigation is not possible, to turn it under before it seriously reduces the amount of moisture in the soil. Disking or plowing should be deep enough to turn under the covercrops or weeds completely, in order to facilitate their decay. In plowing or disking one should avoid injuring the tree roots, espe- cially the larger ones, because such injured places invite crown gall. In soils badly infested with crown-gall organisms, growers often hoe by hand near the tree trunks to avoid injuring the large roots with cultivat- ing implements. The depth of cultivation is commonly varied from time to time to pre- vent plow sole. INTERCROPS In intercropping, the object is to obtain some income before the trees bear. Although not generally to be recommended, intercropping may be used provided the orchard can be irrigated and provided the water is applied to benefit the almond trees rather than the intercrop. Some grow- ers plant intercrops in narrow strips between the rows, leaving consid- erable space between the intercrop plants and the tree rows. Then the intercrop can be irrigated without materially affecting the young trees. •Root crops, strawberries, grains, Egyptian corn, nursery stock, peas, beans, alfalfa, and clovers have been grown between rows of almond trees. Tomatoes are not recommended : although they will thrive with the water supply suitable to young almond trees, they may introduce the verticillium disease. Almond Culture in California 47 COVERCROPS Covercrops, or green-manure crops, differ from intercrops in that they are not removed from the land but are turned under to improve the soil. Covercrops add organic matter to the soil, improve its physical structure, render it more suitable for beneficial soil organisms, and assist in the absorption and penetration of rain and irrigation water. They can usually be grown readily where irrigation is practiced. The difficulty in growing covercrops on nonirrigated lands is that they com- pete with the trees for soil moisture. In dry seasons heavy covercrops cannot be grown on nonirrigated lands. Even in wet seasons, the cover- crop on such soils should be turned under early to prevent it from com- peting with the trees for moisture. In many almond-growing districts of California the difficulty in finding covercrops that will grow well during cold weather in winter has limited their use. Since localities vary as to their climates, some covercrops grow better in certain almond districts than in others. The following facts pertain to covercrops in California. Bur clover (Medicago hispida) is a valuable covercrop. It grows wild in many sections of California, often reseeding itself year after year, especially when the soil moisture is sufficient in the fall. Early rains or the early application of water by irrigation is necessary to get a proper covercrop. Hulled bur-clover seed is often difficult to obtain. As a cover- crop it is seeded at the rate of 20 pounds to the acre. If the burs are planted, more pounds per acre are necessary than of seed. Bur clover is well adapted to the Sacramento and San Joaquin valleys and should be tried out elsewhere. Bitter clover (Melilotus indica) , a yellow clover sometimes called sour clover, often makes a good winter growth under California conditions. It must be planted early in the fall, usually during September. By Feb- ruary it should be 2 or 3 feet high. It is probably the most widely grown covercrop used in California. Usually 20 to 25 pounds of seed is sown per acre. Fenugreek (Trigonella foenum graecum) has long been grown as a covercrop in the southern California coastal regions. Though well adapted to the warmer areas of the coastal sections, it has also thrived in the interior valleys, where it should be regarded as one of the valuable covercrops. It is one of the few legumes that succeed well when sown late, even as late as December. It is also one of the few legumes that can be used on nonirrigated land. While it has been grown upon light, sandy, gravelly, or loamy soils, it is best suited to heavy soils or adobe. It often makes a good growth during February and March. Seed can be sown in 48 California Agricultural Extension Service [Cir. 103 late September, October, or even in December — about 30 pounds to the acre. The vetches, like the clovers and alfalfa, are valuable in adding nitro- gen to the soil. The common vetch (Vicia sativa) has been tried as an orchard covercrop in California. "When planted late it sometimes makes a good stand, but often the results are discouraging. Purple vetch (Vicia atropurpurea) has been found to make a good winter growth. It does especially well in the coastal regions of California. The small-seeded horse bean (Vicia faba var. minor), very promising as a winter covercrop, 16 grows well on heavy silt or clay loams. Seed sev- eral years old germinates well. It is best suited to coastal sections. It is planted at the rate of 80 to 200 pounds per acre. Grain, though sometimes planted as a covercrop, is not recommended. The other plants already mentioned are more suitable. Native weeds of various kinds frequently make satisfactory cover- crops. Mustard makes a heavy growth in practically all almond districts in the state. Its seed remains viable for a long time and may stay in the soil for years awaiting proper germinating conditions. It is easily estab- lished and grows well during late winter. Although it is a serious pest in grain fields, many orchardists in the Sacramento Valley are using it as a covercrop. Five pounds of seed per acre is ample. Alfalfa is sometimes but not often used as a covercrop. Kennedy notes that legumes make a satisfactory green manure crop in certain seasons, but the same legume does not make the most satisfac- tory crop when grown continuously. He advises, therefore, a ten-year rotation using the following crops two years each and in the order given : bitter clover, purple vetch (Vicia atropurpurea) , tangier pea (Lathy r us tingitanus) , 17 small-seeded horse bean, fenugreek. Other rotations also could be used. IRRIGATION Almonds in California need irrigation fully as much as some other or- chard trees. Only in recent years, however, have almond growers realized this fact although publications on the subject have been numerous for a long time. Although young trees may appear to grow well without irri- gation, they often grow more rapidly and produce better foliage when irrigated. It is the older bearing trees, however, that generally show pronounced benefits. The effects of irrigation upon them are especially 16 Kennedy, P. B. The small-seeded horse bean. California Agr. Exp. Sta. Cir. 257: 1-23. 1923. 17 Kennedy, P. B. The tangier pea, Lathyrus tingitanus. California Agr. Exp. Sta. Cir. 290:1-15. 1925. Almond Culture in California 49 Fig. 16. — Orchard irrigated by pumping water from the drainage ditch in the background into the higher irrigation ditch, from which the water is dis- tributed to the orchard. As the water is lifted only a few feet, the cost of pump- ing is very low. Water from drainage ditches should not be used for irrigation if it is known to contain a harmful amount of salts. Fig. 17.— Furrow method of irrigating almond orchard. Before the orchard was planted, the land was properly graded. The water is carried through under- ground pipes. The concrete outlets shown provide a convenient means of con- trolling the water. Underground systems of piping, though expensive to install, are out of the way of orchard operations, so that the water can be applied easily and cheaply. 50 California Agricultural Extension Service [ Cir - 103 marked where the rainfall is light, as in many of the almond-growing districts. Almond orchards are generally irrigated with water supplied by gravity or from wells, but in a few cases, the water is obtained by pump- ing from drainage ditches (fig. 16). The application is by the furrow Fig. 18. -The basin method, one of the common ways of irrigating almond orchards in California. system (fig. 17) , but the simple basin and contour check methods are also used (fig. 18). The different systems of irrigation are explained in sev- eral bulletins to which the reader is referred. 18 As irrigation should supplement rainfall, judgment should be used in the frequency of application and the quantity of water used. The determining factors are the amount and distribution of rainfall, the season, locality, character of the soil and subsoil, topography of the land, cultural methods, and size of the trees. When the rainfall is heavy and especially when some of the rains occur late, less irrigation may be needed than when the rainfall is light or early. If the dry season is long (often from February to November), 18 Fortier, Samuel. Orchard irrigation. U. S. Dept. Agr. Farmers' Bui. 1518:1-27. 1927. Brown, J. B. The contour check method of orchard irrigation. California Agr. Ext. Cir. 73:1-19. 1933. Huberty, M. R., and J. B. Brown. Irrigation of orchards by contour furrows. Cali- fornia Agr. Ext. Cir. 16:1-16. Eevised 1932. Christiansen, J. E. Measuring water for irrigation. California Agr. Exp. Sta. Bui. 588:1-96. 1935. Almond Culture in California 51 more irrigations will generally be needed than if heavy rains last until late in April. A deep soil takes up and retains water either from rainfall or irriga- tion much better than a shallow soil. Deep soils can be heavily irrigated at each application and, as a rule, need fewer applications per season. Fig. 19. — A small irrigation ditch made of cement and small rock is useful in distributing water over porous soils. The shallow soils, whose water-holding capacity is limited, require care- ful and frequent irrigations. If the soil is underlain by hardpan or layers impervious to water, the drainage may be poor unless there is consider- able slope. Whenever impervious layers are present, free water must be prevented from accumulating above the hardpan. If the substrata are gravelly or porous, the water sinks through the soil rapidly. Often much of it is wasted, and certain plant food materials may be leached away. Such soils generaly require frequent and rather light irrigations. Sandy soils absorb water readily, whereas compact soils take it slowly, especially when dry, and require lengthy applications. Jointed pipe is often useful in sandy soils where the seepage losses from open ditches or furrows would prevent uniform distribution of the water. Small concrete ditches placed rather close together are used by some growers 52 California Agricultural Extension Service [Cir. 103 to prevent loss of the water in porous soils and to prevent erosion of the ditches. The water is distributed from various points along the concrete flume and allowed to flow through furrows in the soil until the next lower flume is reached. Figure 19 shows a small concrete ditch made of cement and small stones. The topography of the land has an important relation to the moisture supply. Steeply sloping or sharply rolling lands not only drain rapidly Fig. 20. — Erosion on a hillside after a heavy rain. Contours, ridges, or strips of grass can be used to prevent erosion in orchards planted on such slopes. This hillside is already planted with young almond trees, although they do not show- clearly in this picture. but may have considerable surface runoff. Irrigation and cultural oper- ations are more difficult and expensive on rolling than on level land and irrigation may probably best be accomplished there by contour systems. On steeply sloping lands erosion may take place during heavy rains (fig. 20), and means must be taken to prevent it. 19 Contour planting, leaving strips of grass, and terracing can be used to prevent erosion. Flumes or jointed pipes are sometimes useful in carrying water across depressions in the land (fig. 21) . Cultural methods have a direct bearing upon the amount of irrigation necessary. Cultivation to break up compact surface soils and promote the absorption of water is customary. The growing of intercrops or 19 Eamser, C. E. Farm terracing. U. S. Dept. Agr. Farmers' Bui. 1669:1-21. 1931. Mattoon, Wilbur R. Stop gullies, save your farm. U. S. Dept. Agr. Farmers' Bui. 1737:1-14. 1934. Almond Culture in California 53 (•overcrops, which require much irrigation, influences the quantity and frequency of application of water, although the size of the trees is prob- ably the most important factor because of the soil water removed by the transpiration of the leaves. The larger the trees the more water re- quired. Even in winter when the trees are dormant there is always some activ- ity in them and if the rainfall is deficient irrigation may be necessary to prevent the soil and roots from drying out. Fig. 21. — Wooden flumes of this type are convenient in carrying water across uneven ground. Available soil moisture is especially important throughout the grow- ing season. The grower will find the soil auger useful in determining the moisture conditions in the soil. In addition, the wilting of weeds will generally indicate a need for water before it is shown by the leaves of the trees. Water should always be applied before the trees show the effects of drought. In years of insufficient rainfall, although the surface of the soil is moist, the soil underneath may be dry. When this condition occurs, irrigation in late winter to fill the soil reservoir is a desirable practice. Frequent copious applications of water must be guarded against, especially when old nonirrigated orchards are suddenly brought under irrigation. Such trees sometimes show unfavorable symptoms if water is applied frequently in large amounts. Raising the water table to a marked extent in the summer, especially in old deep-rooted orchards, should be avoided, for it may result in root rot, sour sap, root fungus, diseases, and the growth of numerous water-sprouts. After a time, dying at the tips may occur ; but this symptom is often due to other causes. In deep, well-drained soils there is, of course, less trouble from excessive applications of water than in shallow soils. 54 California Agricultural Extension Service [ Cir - 103 Water should not be allowed to stand too long around the trunks when the basin method is used for irrigation, because under such condi- tions the crowns and trunks sometimes develop such troubles as rot, gummosis, sour sap, rot, and softening of the bark. Irrigation aids considerably in controlling red spiders, which do not thrive when the leaves transpire moisture readily, but which often be- come extremely troublesome when the normal transpiration is curtailed. To a certain extent, sticktights can be prevented by proper irrigation. A large percentage of the almond hulls do not open, or at least hulling is difficult if the soils are dry for a considerable time before harvest. Whether one should irrigate when the hulls begin to split depends upon whether or not the soil is dry. If the trees and nuts show the need of water, one should not hesitate to apply it, though the irrigation may somewhat delay the ripening of the nuts. Some irrigation water contains harmful minerals and salts which, when applied to the soil over a period of years, may greatly injure the trees. In some sections boron in the irrigation water has affected or- chards, 20 but to date very few almond orchards have been thus damaged. In recent years, water pumped from wells has contained various salts that injured almond trees in some localities. Common table salt (sodium chloride) has often caused considerable damage. Water from drainage ditches should be used only if free from harmful salts. Irrigation affords an effective means of increasing yields ; in practi- cally all instances the bringing of nonirrigated trees under irrigation has greatly increased the crop. DRAINAGE The effect of drainage upon the almond has been mentioned under soils. Good drainage is very important, especially in irrigated orchards. Nat- ural drainage depends upon the character of the soil and subsoil, the presence of hardpan, and the slope of the land. One should obtain well- drained land for the orchard rather than try to correct defects later. FERTILIZATION Barnyard manure usually produces larger yields, improves the soil texture and fertility, and increases the vigor of almond trees. In a few instances, however, especially on impoverished sandy soils, heavy appli- cations have had harmful effects, first seen in a yellowing of the leaves 20 Scofield, Carl S., and L. V. Wilcox. Boron in irrigation waters. U. S. Dept Agr. Bui. 264:1-65. 1931. Eaton, Frank M. Boron in soils and irrigation waters and its effect on plants with particular reference to the San Joaquin Valley of California. U. S. Dept. Agr. Tech. Bui. 448:1-131. 1935. Almond Culture in California 55 and in unthrifty twig- growth. The reason why barnyard manure may produce these results is not known. On light impoverished soils, care should be taken not to apply it in great quantities. On the whole, harm- ful effects are rather exceptional when compared with the benefits ; and barnyard manure applied in moderation is probably the best method of fertilizing an orchard, although in most almond-growing districts it is difficult to obtain. Commercial fertilizers have been applied to almond orchards with varying results. Upon poor soils especially, some benefit might be ex- pected ; but in practice this has not always resulted. To be profitable the use of fertilizer must increase the yield sufficiently to more than offset the cost of the material and its application. In some instances nitrogen has been apparently beneficial ; but thus far there are no data showing benefits from potash or phosphoric acid. 21 Almond hulls as a fertilizer have been considered of doubtful value because of the tannin they contain. Whether or not they are detrimental to the soil is a question. Some growers who have scattered the hulls in their orchards with manure spreaders for several successive years report considerable benefit, both in tree growth and yield and in improving the soil texture. Further trials will be necessary before there is definite in- formation regarding- their fertilizing* value. If used, the hulls should probably not be applied too thickly. Sufficient moisture, too, is neces- sary to cause them to decay properly. Some growers have covered their yards with several inches of almond hulls each year to keep down weeds. At first the applications seemed to accomplish the purpose ; but after a few years, when the hulls had decayed, grass and weeds grew abun- dantly. Colby 22 reported that one ton of almond hulls contained 23.65 pounds of potash, 2.35 pounds of phosphoric acid, and 6.00 pounds of nitrogen. The use of lime to correct soil acidity and to improve the texture of heavy soils is sometimes desirable if it is not too expensive. Most almond orchards, however, are on neutral or slightly alkaline soils. The addition of lime may prove injurious to almond orchards on peach root. The cir- culars cited in the footnote contain material of interest on fertilizers for California soils. 23 21 Proebsting, E. L. Field and laboratory studies on the behavior of NH 4 fertilizers with special reference to the almond. Amer. Soc. Hort. Sci. Proc. 33:46-50. 1936. 22 Colby, George E. Fruits, tanning materials, hops, etc. California Exp. Sta. Rept. 1898-1901:261. 1902. (Out of print.) 23 Hoagland, D. R. Fertilizer problems and analysis of soils in California. Cali- fornia Agr. Exp. Sta. Cir. 317:1-15. Revised 1934. Hibbard, P. L. Commercial fertilizers and soil fertility in California. California Agr. Ext. Cir. 57:1-38. Reprinted 1933. 56 California Agricultural Extension Service t ClR - 103 PRUNING Young- nonbearing almond trees are pruned to shape the tree and to secure the right number and correct spacing of the scaffold or main branches. Bearing trees are pruned to thin out undesirable branches, to regulate the amount of light admitted to the trees, to encourage the proper development of buds and foliage, to secure the most desirable bearing surface, and to remove dead or diseased twigs or branches. Pruning properly begins with the planting of the young nursery tree in the orchard and continues throughout the life of the tree. When planted, the tree is generally cut back to a whip about 27 inches long. In rare cases, if good laterals occur where wanted, they may be saved and shortened to 8 or 10 inches. As a rule, all the laterals are cut off nursery trees, leaving stubs % inch long. The framework branches must be grown from dormant buds or from adventitious buds around the wounds caused by removing the laterals. In the spring, the trees should be gone over carefully and the branches desired for the framework selected. At this time the growth is only a few inches long, and the undesirable shoots are easily subdued by pinching out their terminals. This procedure will encourage the development of the framework branches, which should be allowed to grow untouched. The undesirable shoots should not be re- moved entirely, because their leaves manufacture plant food and by shading help to prevent sunburn of the trunk. If a tree is allowed to grow the first summer without this attention, three to five of the uppermost buds will develop into strong branches by the end of the growing season, while only short twigs will develop from the buds lower down on the trunk. These low, short twigs cannot be used as framework branches and in that case, it will be necessary to select the three framework branches all arising from practically the same point on the tree (fig. 22), a condition which in later years results in crowding of the branches and the formation of water pockets. In the best type of head, the branches are spaced as far apart as possi- ble along the trunk (6 inches to a foot or more apart). The height and spacing of the main branches in the young tree determine their position in the old tree. Because the trunk does not lengthen, the framework branches in the old tree will be the same height from the ground and the same distance apart as on the young tree ; but, because of their larger diameter, the main branches of the old tree will appear closer together than the}^ do when the tree is young. By remembering this, the grower when pruning the young tree will be able to visualize the relative posi- tion of each branch on the older tree and will therefore be able to secure Almond Culture in California 57 better spacing of the branches than otherwise. The ideal is to have three branches (more will cause crowding) spaced at least 6 inches apart and arranged spirally around the trunk, forming equal angles of about 120 degrees. Fig. 22. — Improper framework on young tree. The branches for the framework are too close together. When the tree reaches bearing age it will suffer from weak crotches and water pockets. These undesirable conditions can be avoided by proper pruning methods. The best way to get strong secondary branches where they are desired is to pinch out, during the summer, the tips of all poorly placed shoots to check their growth and stimulate the growth of shoots that are suit- ably placed. 58 California Agricultural Extension Service t ClR - 103 Fig. 23. — One-year-old Nonpareil tree before pruning. At the time of planting, the laterals were saved and headed at A. (From Cir. 284.) Almond Culture in California 59 Pruning One-Year-Old Trees. — The first winter's pruning- may be done at any time after the leaves fall, approximately one year after planting. If summer pinching has been done as directed, very little Fig. 24. — Same tree as figure 23 after pruning. The tree was thinned to lat- erals, which were headed moderately. Often the laterals should not be headed if a desirable shape can be secured without shortening them. (From Cir. 284.) pruning will be needed. Often the three scaffold branches can be cut back to a lateral, leaving them from 15 to 30 inches long. This length is determined by the variety of almond and by the growth the tree has made. 60 California Agricultural Extension Service [Cir. 103 A variety with a spreading habit of growth such as the Drake will be headed back more severely than an upright variety such as the I. X. L. If the trees grow very vigorously during the first summer, they may need heading when they have grown 15 to 30 inches. In this case a secondary branching may be secured during the first summer, and the first winter's pruning will be only a thinning out, since enough framework branches Fig. 25. — Six-year-old Nonpareil tree, moderately pruned. (From Cir. 284.) have been secured. If the trees grow very poorly during the first season, they should receive no pinching out in the summer and little or no prun- ing the first winter so that they may have as much leaf surface as possible to build up the tree and make a strong, healthy growth the second season. Figure 23 shows a Nonpareil tree, before pruning, after one season's growth. At the time of planting, the laterals were saved and headed at A. Figure 24 shows the same tree after pruning. Often, however, well- spaced laterals develop the first season, and it is not necessary to cut back in order to secure the five to seven branches up to shoulder height which are desirable in the mature tree. Pruning During the Second Season. — During the second season un- desirable branches that may grow at the expense of the desirable fram- Almond Culture in California 61 work should be removed. Since the almond makes numerous lateral branches, the framework branches usually need no heading the second season. If no pinching has been given during the second spring and summer, the water-sprouts and ill-placed branches must be removed. Occasion- ally, when a tree has made an unsymmetrical growth, a water sprout may serve to advantage as a framework branch if growing in the proper Fig. 26. — Left: Improper way of cutting a large branch. Where a stub is left, healing-over does not take place properly, and wood-destroying fungi may then cause the stubs as well as the main branches or trunk to decay. The stub shown in this picture has become infected by wood-decaying organisms. Eight: Proper way to remove a large branch so as to leave no stub. Proper healing over is taking place. It is desirable to protect the cut surface with paint or other preparation to prevent checking and decay of the wood. position to fill a vacancy. Generally no heading is necessary, especially if the tree at this time has five to seven branches and sufficient spread. Pruning During the Third and Fourth Years. — In the third and fourth years, if the trees have been pruned according to the suggestions given above, the only work necessary will be a thinning out with no head- ing. Such trees should produce a considerable crop of nuts the fourth summer after planting and should thereafter be handled as bearing trees. Pruning Bearing Trees. — Bearing almond trees are usually pruned lightly merely by thinning out the branches to admit light and removing the interfering branches. The branches are shortened only to modify the shape of the tree or to induce shoot growth. The amount of thinning out 62 California Agricultural Extension Service [ Cir - 103 will depend upon the condition of the trees and their location. In the hot valleys less thinning is necessary to admit sunlight to the central portion of the tree than in the cooler regions. The commercial practice in almond pruning consists mainly in re- moving water sprouts and branches about % inch in diameter, with no attention to the one-year shoots (fig. 25). Occasionally a larger branch must be removed when it begins to interfere or crowd. The trees must be kept open so that sunlight can strike the leaves and maintain a healthy condition of the buds and fruit spurs in the lower and central portions ; otherwise fruiting will be confined to the upper and outer area. Nor- mally, bearing almond trees are not expected to make more than 8 to 15 inches of new shoot growth each year. If they make much longer growth, pruning may be discontinued for a year or more, which throws the trees into heavy production and slows down the vegetative growth. After regular bearing is established, a moderate pruning should be given to get the trees back into proper shape. If, on the other hand, they are mak- ing little or no growth, some of the fruiting branches should be removed to invigorate the trees. Very often, however, the lack of growth is caused by deficient soil-moisture conditions and cannot be materially remedied by pruning alone. In old orchards where pruning has been neglected for several years, the larger branches may need thinning out (fig. 26) . Generally, however, it is best to thin them out gradually from year to year, because heavily pruned old trees often require several years to come back into produc- tive bearing. REJUVENATION OF OLD TREES During the last few years, many of the older orchards have been decreas- ing in production — often at the very time when increased crops would normally be expected. There are a number of reasons. Improper root- stock has been found to be a common cause. Almond trees propagated upon the poorer types of peach stock often begin to decrease in produc- tion at twelve to sixteen years. Diseases such as severe crown gall or heart rot are sometimes responsible for low yields. Girdling of the roots by gophers and other rodents or continued destruction of the foliage by the red spider also weakens the trees. Poor soils, lack of drainage, and lack of soil moisture may cause gradual decline. Much can be done by avoiding or correcting any of these conditions. The rejuvenation of old trees by severely cutting back the top, al- though widely advocated, is at best of temporary value. Trees thus headed generally produce an abundance of new growth and commonly begin to bear the third year after the operation ; but there are several Almond Culture in California 63 objections to the method. No crop whatever is borne for two years. The pruning wounds are large and do not heal for a long time; and unless they are carefully protected by proper painting, they afford ready en- trance to disease organisms. Generally the new shoots do not have a very strong union with the stubs and may be blown off in windy weather after they come into bearing. Considerable work is necessary to thin out the brushy tops produced by deheading. Frequently trees thus rejuvenated begin to decrease in production after the first few crops. The deheading method is recommended only as a temporary measure. It is generally more profitable to interplant the old declining orchard with young trees and, as they come into bearing, to remove the older non- bearing trees. ALMOND DISEASES 24 Diseases are often troublesome in almond orchards and control measures involve considerable expense and careful attention. Almond diseases are of two types : parasitic, caused by low forms of plant life known as bacteria and fungi ; and nonparasitic, not caused by organisms but probably by environmental or nutritional conditions. PARASITIC DISEASES The following discussion is confined to parasitic diseases occurring in California. Many fungus troubles found in other parts of the world are not mentioned. Some diseases listed are of minor importance, while others, in their destructiveness to the crop or to the trees, are often a serious menace to almond production. Many of the diseases attack other stone fruits. Some, in consequence, are known by one name on one stone fruit and by another name on some other stone fruit. For example, "peach blight" is caused by the same fungus as the "shot-hole" of almonds and apricots. Two distinct diseases, the brown rot and the green rot, are often confused. Green rot denotes the attack of a particular fungus on green almond fruit, but the entirely different brown-rot fungus may attack green fruit of the cherry, peach, apricot, and plum; this sometimes causes confusion. The rotting of green almond fruit, in the Sacramento Valley at least, is usually due to the green-rot fungus and not to brown rot. Methods of Control. — Control methods, when known, will be discussed along with each disease. They fall under the following general headings : (1) planting in localities where the disease is not serious, (2) planting resistant or immune varieties, (3) planting healthy trees, (4) removing 24 The section on almond diseases was prepared by E. E. Wilson, Division of Plant Pathology, University of California. 64 California Agricultural Extension Service [ Cir - 1q 3 and destroying diseased parts of the tree, and (5) preventing infection by means of sprays or dusts. In practice the last three methods are often- est used, since a disease is seldom restricted to definite localities and since few desirable resistant or immune varieties are known. Brown Rot. — Brown rot, caused by the fungus Sclerotinia fructicola, attacks the blossoms. As these wither and die, the fungus passes into the Fig. 27. — Brown-rot cankers on almond branches. The disease en- tered through blossoms, the remains of which can still be seen in the left-hand figure. Spore masses are visible on the surface of the cankers. (From Bui. 326.) twigs, either blighting them or producing elongated, sunken cankers (fig. 27). Diseased parts harbor the fungus until the following spring, when it spreads by means of spores to the blossoms. In control, therefore, blighted spurs and terminals must be removed from the tree and de- stroyed before blossoms appear. Thus far the only sprays found effective in preventing blossom infec Almond Culture in California 65 tion are those applied in the spring when the blossoms appear. Slight benefit has been derived from spraying in the dormant season. Since the blossoms are liable to infection as soon as they appear between the scales of the winter buds, a spray should be used at this time — the "pink-bud" application. If rains occur between this stage and the end of bloom a second spray is necessary, since that applied at the pink-bud stage covers only the ends of petals in the unopened blossoms. This second spray should be applied as soon as all the blossoms have emerged from the winter buds — in most years, when the earliest blossoms have opened. Bordeaux mixture, 8-8-50, is recommended for these applications. The applications cannot be timed, of course, to cover the blossoms of all varieties at the same stage. Fortunately, only one important commer- cial variety, the Drake, is usually severely affected by brown rot. In orchards where the Drake has been diseased for several years, however, the Ne Plus Ultra, I. X. L., and other varieties may show considerable disease. Since the Drake is usually first attacked and is subsequently a source of the fungus, the spray applications should be timed to protect this variety as much as possible. Green Rot or Jacket Rot. — The disease caused by the fungus Sclero- tinia sclerotiorum is often mistaken for brown rot because it rots the young fruit. First a watery, discolored area develops on the fruit be- neath the jacket or old calyx cup. The fungus attacks the jacket before it is shed and later enters the young fruit. No spores are noticeable on fruit attacked by this disease. Several attempts have been made to control green rot with sprays. In at least one instance bordeaux mixture, 3-3-50, applied during full bloom, apparently has reduced green rot considerably. Bordeaux mix- ture applied after flowering before the jackets are shed, has generally failed because the jackets prevent the sprays from covering the young fruit and because the fungus, growing directly from the jacket into the fruit, does not come into contact with the spray. Attempts have been made, with some apparent success, to cause bordeaux to penetrate the jackets by adding a light oil to the spray. Some growers hasten the drop- ping of the jackets by jarring the branches with almond clubs. Shot-Hole. — The disease known as shot-hole is caused by the fungus Coryneum beijerinckii (fig. 28). It destroys fruit buds, causes defolia- tion, and produces malformation of the fruit. Attacked fruit buds fail to open in the spring, are dark brown to black in color and may exude gum. The first symptom on twigs is a small purplish spot, later enlarging into a circular, brown area with a sunken center and raised, cracked margins. Defoliation usually occurs early in the season because older leaves do not 66 California Agricultural Extension Service [Cir. 103 fall so readily, but are more inclined to drop out the diseased areas, thereby developing the typical shot-hole condition. The fungus apparently passes its entire life cycle on the tree ; it does not develop a stage in the soil or on fallen leaves. Instead it is harbored in twigs and buds; and when the winter rains begin, the spores from these diseased parts are spread throughout the tree. If the fungus is prevented from attacking dormant buds and twigs, a high degree of control of fruit and leaf infection is obtained. This is Fig. 28. — Effect of the shot-hole disease on almond foliage. the same principle involved in controlling the disease on peach and apri- cot by applying 5-5-50 bordeaux in the autumn after the leaves are off. The best time for preventing bud infection of the almond has not yet been determined. In 1935 fairly successful control was obtained by ap- plying bordeaux in late January before the buds had swelled appre- ciably. Spraying when the first leaves appeared also aided in control but was less effective than spraying in January. As far as possible, all affected parts should be removed, for once the disease in the tree is reduced to a small amount, control by spraying is more successful. Cercospora Leaf-Spot. — Occasionally the fungus Cercospora circum- scissa causes a leaf -spot of almonds. As a rule, these spots are consider- ably larger than those produced by Coryneum beijerinckii but are other- wise somewhat similar. The Cercospora spot is rare and for it no control Almond Culture in California 67 methods have been devised. Spraying the foliage with bordeaux mixture would be expected to give some control. Oak-Root Fungus or Armillaria Root Rot. — A disease caused by the fungus Armillaria mellea (fig. 29) attacks the roots and crowns of al- mond trees. The aboveground symptoms are pale-green foliage, cessation of growth, and finally death of the tree. Certain other diseases may be confused with it, but armillaria root rot is distinguished by the presence Fig. 29. — The white, leathery, fan-shaped growth of the oak-root fungus beneath the bark. (From Ext. Cir. 98.) of yellowish-white, leathery, fan-shaped mycelial layers between the bark and the wood of affected parts. Frequently there will be found along the surfaces of diseased roots and in the surrounding soil dark-brown to black, rootlike strands or rhizomorphs, by which the fungus spreads from the roots of diseased trees to those of adjacent healthy trees. The fungus is frequently present in virgin land as a parasite on the roots of native trees, particularly oak, and infected spots may develop in soil where pieces of diseased native roots have been allowed to remain. In removing diseased orchard trees all infected parts should be destroyed. 68 California Agricultural Extension Service [Cir. 103 Once established in an orchard, the fungus cannot be easily eradicated. In southern California citrus soils, carbon disulfide has been used to kill it with a fair amount of success. The method has not, however, given en- couraging results in deciduous orchards of central California, particu- larly in heavy, wet soils. Preventing spread from diseased to healthy trees by digging trenches or constructing underground barriers, although fairly successful, has proved impractical. The life of trees surrounding an infected soil area has been prolonged by exposing the crown and main roots to the air, removing infected roots, and sterilizing the cuts with a solution of 1 part corrosive sublimate, 250 parts of denatured alcohol, and 750 parts dis- tilled or rain water. The crown and roots are then left exposed for a month or more during the summer to permit the drying out of any dis- eased area that was not removed. By inspecting every year one can detect the fungus as it extends inward along the roots in time to prevent its reaching the crown. Since most trees and shrubs are attacked, only a few can be planted in infected areas. The French pear, the fig, and the northern California black walnut are considered highly resistant. Apples are less susceptible than stone fruits, and Myrobalan plum less so than the almond, although not sufficiently resistant to permit their use in badly infected soil. Where none of these fruits is desired the land may be planted with almost any field or truck crop except potatoes and rhubarb. Black Heart or Verticilliosis. — Black heart, caused by the fungus Ver- ticillium alboatrum, is first indicated by a sudden wilting of leaves in early summer. The tree may be killed outright, in which case the leaves may remain hanging for some time ; or it may drop its leaves and then, apparently recovering, will produce new foliage. ^ The fungus, living in the soil, attacks through the root system, causing a dark-brown discoloration of the sapwood. The wood of roots, trunk, and even the smallest branches may be affected. As a wide range of plants is susceptible, the fungus may be present where almonds have never been planted. Soils upon which tomatoes have grown are fre- quently infected. No effective control is known. Bust. — Caused by the fungus Tranzscehlia punctata, rust is rarely important. It is found occasionally in coastal districts, usually appear- ing late in the season as red or brown spots on the undersides of the leaves. Severely infected leaves will fall. No control has been devised. Crown Rot. — A disease similar to that induced in nursery trees by the fungus Phytophthora (Pythiacystis) sp. has caused considerable trouble Almond Culture in California 69 in young orchard trees the past few years. Trees attacked by crown rot will either fail to start growth in the spring or, after producing a full crop of leaves, will die during the first hot days of early summer. A dead sunken area will be found to have girdled the crown of the tree at the ground level. Often considerable gum is produced around the base of the trunk. In many respects this disease resembles bacterial canker. In its Fig. 30. — Crown gall on almond roots. (Courtesy Bureau of Plant Pathology, California State Department of Agriculture.) sudden killing of the tree it resembles blackheart ; but it differs in not discoloring the sap wood for any great distance above the diseased area. Many cases of the so-called "sour-sap" are undoubtedly caused by this fungus, since the disease is more prevalent in years of heavy rainfall when the soil about the crown remains wet for a long period. Trees planted too deep or located in low, wet areas will suffer more than those favorably placed. Usually the grower first notices the disease too late to save the badly affected trees. No preventive is known. All that can be done is to remove the soil from about the crowns, allowing them to dry thoroughly during the summer. Crown Gall. — Caused by the bacterium Bacterium tumefaciens, crown gall produces rough, woody, irregularly shaped enlargements of various sizes on roots, crowns, and occasionally limbs (fig. 30). Badly affected trees bear a poor crop of light-green leaves, shoot growth is lessened, and death may ensue. 70 California Agricultural Extension Service [Gib. 103 The crown gall organism attacks a wide range of trees, shrubs, and even herbaceous plants, and may therefore be present in soils where these plants have grown. Virgin grasslands on the other hand, are less apt to contain the bacteria. Since many commercial almond varieties are highly susceptible, they should preferably not be planted in soils for- merly growing such crops as grape, quince, blackberry, and raspberry. The nursery trees should be inspected, before being placed in the soil, and any with galls should be discarded and burned. Care should be taken to avoid wounding orchard trees near the crown. Diseased orchard trees are benefited somewhat by removing the soil from around the crown, cutting out the galls and the bark tissue sur- rounding them, and covering the wounds with bordeaux paste. This measure is, of course, justified only with profitable producers ; it cannot rehabilitate trees in the last stages of the disease. Bacterial Gummosis or Bacterial Canker. — Caused by the bacterium Pseudomonas cerasi, bacterial gummosis is less destructive to almonds than to other stone fruits. Some loss of Nonpareil and Ne Plus Ultra has occurred. Elongated cankers develop in the bark of limbs and trunks, usually exuding considerable gum. Sometimes, however, no gum is pro- duced ; but the diseased bark develops a moist, sour-smelling condition known in some localities as "sour-sap." This is not to be confused with the sour-sap that results from killing of roots and crowns by other agen- cies, since the bacterial trouble does not commonly affect the roots. Un- doubtedly, death of trees from this disease has sometimes been errone- ously ascribed to too much irrigation water. No effective control method is known ; but in the first stages considerable benefit may be derived from cutting away all the diseased area and painting the cut with bor- deaux paste or some other good protective. NONPARASITIC DISEASES Little-Leaf. — Little-leaf is prevalent in certain sections. Affected trees produce small, yellowish leaves, sometimes bunched together on the ends of the twigs; but the symptoms are generally less pronounced in the almond than in other trees. According to W. H. Chandler, of the Uni- versity of California, and others, little-leaf may be remedied by zinc applied by injecting zinc solutions into the trunk, by spraying, by driv- ing zinc metal into the branches, and by applying zinc compounds to the soils. He states that to date spraying has given the best results in case of the almond. One-fourth pound of zinc sulfate to 1 gallon of water ap- pears to be the best spray and application should be made in December, but never after the buds swell. Almond Culture in California 71 Fruit Gumming. — Almond fruit attacked by the shot-hole disease will frequently produce gum. There is, however, an unrelated trouble in which large amounts of gum are produced within the shell and ex- truded to the surface along the suture. The cause, though unknown, is apparently related to some unfavorable growth condition. INSECTS AND OTHER PESTS OF ALMONDS 25 Mites. — Certain mites, commonly called red spiders, are serious orchard pests. Four kinds attack almond trees : the common red spider or two- spotted mite; the Pacific mite; the brown mite, also called the almond Fig. 31. — Typical appearance of the adult females and eggs of three species of red spider. Left, the common red spider, Tetranychus telarius ; center, the brown or almond mite, Bryobia praetiosa; right, the European red mite, Para- tetranychus pilosus. All greatly enlarged. (From Bui. 347.) mite; and the European red mite. These are discussed further in the publications cited in the footnote. 26 The common red spider or two-spotted mite (Tetranychus telarius) is pale green with occasionally a reddish tinge, and usually with two dark spots on each side of the body (fig. 31) . The Pacific mite (Tetrany- chus pacificus) is yellowish with three dark spots on each side of the body. Both species spin webs ; both spend the winter and early spring on weeds, hardy cultivated plants, or protected parts of the host plant. Dur- 25 The section on insect pests was prepared by J. F. Lamiman, Instructor in Ento- mology and Junior Entomologist in the Experiment Station. 26 Essig, E. O., and W. M. Hoskins. Insects and other pests attacking agricultural crops. California Agr. Ext. Cir. 87:1-155. Eeprinted 1935. Newcomer, E. J. Orchard insects in the Pacific northwest and their control. U. S. Dept. Agr. Cir. 270:1-76. 1933. 72 California Agricultural Extension Service [ Cir . 103 ing the warm days of early summer, generally in June, the mites appear on the trees, usually in the tops or at the tips of the branches, spinning a fine web on the leaves, generally on the upper surfaces. They suck the plant juices from the leaves, which assume a yellowish mottled appear- ance and soon die and drop to the ground. In serious infestations the trees are often almost completely defoliated by the end of August (%. 32). The brown mite (Bryobia praetiosa), which does not spin a web, is dark red or brown in the adult stage, has a flattened back, and can be Fig. 32. — Almond trees partially defoliated by red spiders. easily distinguished from the other species of mites mentioned by its very long front legs (fig. 31) . It works on the green bark of the small twigs as well as on the leaves, sucking the plant juices from beneath the surface. The leaves become mottled and eventually fall, although not so notice- ably as when attacked by the two-spotted mite. The injury to the tree is just as great because of the serious drain on its vitality and because of the early attack, most of the injury being done in the spring and early summer. This mite may spend its entire life on the tree ; the very small, round, red eggs, found most often on the undersides of the branches and in cracks and crevices in the bark and twigs, remain on the tree through- out the winter and hatch early in the spring soon after the leaves begin to develop, the white egg-shells being left in place. Almond Culture in California 73 The European red mite (Paratetranychus pilosus) is generally less abundant on almonds than either the brown or the two-spotted mite. It is deep red and much smaller than the almond mite — almost too small to be seen with the unaided eye (fig. 31) . Its life history resembles that of the brown mite, for the winter is spent in the egg stage on the host of the previous summer. This insect is discussed by Newcomer and Yothers. 27 Although the various species of mites differ in their habits, they cause similar injury. The damage to the foliage and young bark checks the proper functioning of the leaves, weakens the tree, and often causes the leaves to drop prematurely, and thus prevents the normal development of the nuts during the current season. The fruit buds, furthermore, are often weakened, and the crop the following season may be lessened. Mites thrive in a warm, dry atmosphere. They attack trees suffering from lack of moisture or weakened by other causes. Frequently the tree rows along dry, dusty roads are more heavily infested than the rest of the orchard. On trees with thrifty foliage and well supplied with mois- ture, the severity of attacks is lessened because of the transpiration of moisture by the leaves. Irrigation is important in lessening the ravages of the red spider, even where spraying is done. Early cultivation to destroy wild host plants, such as malva and wild morning-glory, aids in retarding the development of the common red spider. This fact should not, however, be used as an argument against the growing of suitable covercrops that are not host plants, such as mustard, and legumes (including bur clover and the other clovers). Growers who have kept such covercrops under irrigation in the summer report beneficial results so far as the red spider is concerned, though such experiences have not been extensive. These cultural methods are not applicable to the brown mite and the European red mite, which must be controlled by spraying and by providing a proper amount of soil mois- ture. The brown mite may be controlled satisfactorily in the egg stage with a dormant spray of lime-sulfur solution, 1 gallon to 10 gallons of water, applied thoroughly just before the buds open in the spring ; or with 3 per cent dormant tank-mix oil spray ; or with 4 per cent commercial dormant oil sprays. The oil sprays are also recommended for the European red mite. During the growing season dry dust sulfur — the finest grade of "dust- ing sulfur" — is often very effective when the mites first appear, pro- vided the weather is satisfactory. Usually it must be applied several times with dusting machines for the best results. 27 Newcomer, E. J., and M. A. Yothers. The biology of the European red mite in the Pacific northwest. U. S. Dept. Agr. Tech. Bui. 89:1-69. 1929. 74 California Agricultural Extension Service [Cm. 103 Mites already established may be controlled in summer with 5 pounds of sulfur, % pound of casein spreader, and 1% gallons of liquid lime- sulfur added to 100 gallons of water ; or with l 1 ^ per cent commercial summer oil sprays ; or with iy 2 per cent summer tank-mix oils. Dormant sprays are not effective for controlling the common red spider or the Pacific mite ; but the summer sprays given above are all satisfactory if applied under high pressure — 300 pounds or more. Because these mites develop rapidly, control is sometimes difficult. Spraying must be thorough. Even with the most careful applications Fig. 33. — Shoots and twigs of almond showing characteristic wilting and dying caused by the larvae of the peach twig borer. (From Ext. Cir. 87.) some leaves may be missed, and from these the mites will multiply and spread. Repetition of the sprays is therefore necessary to keep the mites under control. The development of spider-resistant almond trees offers considerable promise. The breeding experiment conducted cooperatively by the United States Department of Agriculture and the University of Cali- fornia has already produced several hybrid trees unquestionably re- sistant to mites. Although these trees do not produce nuts suitable for commercial purposes, attempts will be made to breed their spider-re- sistant qualities into outstanding varieties. The Peach Twig Borer. — The peach twig borer (Anarsia UneateUa) is widely distributed in California almond orchards. It often causes serious damage of two types : first, the larvae bore into the buds and young twigs, and cause their death (fig. 33) ; second, the larvae enter the fruit. Sometimes after the shell of the nut has hardened the larvae bore into the hull only ; but when the shell is soft or only slightly hardened, the larvae penetrate the shell and work upon the kernel, generally eating grooves along its surface. Often the damage is considerable. In some years infestations have demoralized certain markets. Even if the per- Almond Culture in California 75 centage of infestation is low, a few "wormy" kernels to the pound makes the nuts unmarketable and gives the product a bad name. By methods devised several years ago by the writer for the U. S. Department of Agriculture, cooperating with the California Almond Growers' Ex- change and other organizations, the infested nuts can be separated from the rest ; therefore, wormy nuts are now seldom found in the markets. The peach worm is so damaging, however, that control methods must be practiced in many orchards. The habits of the insect are described by Duruz 28 as follows : The insect passes the winter in the larval stage underneath the bark in small bur- rows constructed in the crotches of the young branches. In early spring the larvae come out and begin feeding on the buds and shoots. When the insects are full grown they crawl down the branches to the trunk where they pupate in the curls of the rough bark. The adult moths emerge in early summer and begin egg laying on the twigs (fig. 34). About the first week in June a second generation of larvae begins to attack the twigs and particularly the fruit. Later in the summer a third generation emerges in some sections and causes serious injury to late-ripening varieties of the fruits attacked. The fourth and last generation of larvae comes out late in September and begins at once to construct chambers and go into hibernation for the winter. These are also known as the first generation larvae of the following year. Duruz states that a larval parasite (Hyperteles lividus) in some seasons destroys as high as 95 per cent of the hibernating larvae. The parasite may therefore be important in controlling the pest and its at- tack explains the fact that sometimes in unsprayed orchards a year of heavy infestation is followed by a year of light infestation. Since, how- ever, the parasite cannot yet be depended upon for control, spraying must be resorted to. Dormant spraying with standard lime-sulfur (1-10), applied under high pressure just as the buds are opening in the spring, has long been the common method of controlling this pest. A more satisfactory remedy, however, is 3 pounds of basic arsenate of lead to 100 gallons of water, applied when the petals of at least two-thirds of the blossoms have fallen, to avoid poisoning of honeybees. If summer arsenical sprays are necessary to control severe infesta- tions, local authorities should be consulted. Because there are several generations a year of this insect, spraying thoroughly to stop the first generation should be practiced. The entire tree, including the young twigs, should be thoroughly covered. In infested orchards any prunings should be collected and burned so that no larvae may be harbored until spring. Infested hulls should also be burned or destroyed. Pacific Peach Tree Borer. — The Pacific peach tree borer (Aegeria 28 Duruz, Willis P. The Peach-twig borer (Anarsia lineatella Zeller). California Agr. Exp. Sta. Bui. 355:419-64. 1923. (Out of print.) 76 California Agricultural Extension Service [Cir. 103 opalescens) should not be confused with the peach twig borer just de- scribed. Its white caterpillars do not work upon the young twigs and fruit, but burrow under the bark near the surface of the ground. The pest is serious in many parts of the state. The larvae may be detected by the frass and gum at the burrow entrances. If allowed to work unmo- lested, they will commonly girdle the tree. The surest means of control is to dig out the worms with a knife or to kill them with a wire probe. This work should be done systematically in Fig. 34. — Adult moths of the peach twig borer, Anarsia linea- tella (enlarged), which also attacks the almond. (From Bui. 355.) the fall and spring, and the wounds covered with a good asphalt paint. The use of paradichlorobenzine is effective. In California this chemical is usually applied between the first of May and November, and when the soil temperature is over 55° Fahrenheit and the soil moisture is not excessive. From % to 1 ounce of paradichlorobenzene is used for an average-sized tree. First level the surface of the soil around the base of the tree. Then sprinkle the material around the tree in a continuous band or circle 2 inches wide, with the inner margin of the circle 2 to 4 inches from the bark. Cover the material with soil around the base of the tree to a depth of 2 to 4 inches, and pack well with several strokes of a shovel (fig. 35). Red-humped Caterpillar. — Red-humped caterpillars (Schizura con- cinna), though not found on almond trees so often as on some other orchard and shade trees, sometimes cause damage in late summer and early fall. They are striped in red, black, and yellow, and are easily dis- tinguished by the red hump on their backs. Whatever colonies appear must be promptly destroyed, for these insects are voracious feeders and Almond Culture in California 77 will denude trees of the foliage in a few hours. Cutting out and burning entire colonies is effective. Spraying with arsenate of late as for codling moth, or dusting with powdered standard arsenate of lead thoroughly mixed with equal parts of hydrated lime is recommended. Thrips. — Of the common species of thrips, three have been reported from the almond : the pear thrips (Taeniothrips inconsequens) , the grain or flower thrips (Frankliniella Occident alls) , and the bean thrips (Her- cothrips fasciatus). The pear thrips are present only in the spring in Fig. 35. — The ring method of applying paradichlorobenzene to the soil. The first step (left) : level the surface of the ground for a space of 2 or 3 feet in diameter about the tree. Second step (right) : the chemical is applied in a ring 2 or 3 inches wide, the inside being about 3 inches from the bark of the tree. (From Bui. 411.) the buds and blossoms. The grain thrips appear at the same time and may also be found on the young leaves and nuts, particularly the larvae. In midsummer and early fall the bean thrips are often found on the foliage. Such infestations may be controlled by spraying with summer oil (or commercial oil) emulsion, 2 per cent, to which is added % pint of nicotine sulfate for each 100 gallons of the spray. Aphids. — The several kinds of aphids found on the almond are seldom serious. Nicotine sulfate preparations such as "Black Leaf 40," diluted as for thrips, will control them. Scale Insects. — Various scale insects, including the San Jose scale, thrive upon the almond but to date have not been regarded as serious pests. When they are found, some "cleanup" spray may be effective, such as a 1-10 lime-sulfur, or a 4 per cent tank-oil emulsion, or 5 per cent 78 California Agricultural Extension Service [Cir. 103 commercial oil emulsion applied during the winter. The following for- mula for oil emulsion with caustic soda may be used : commercial oil emulsion (100-120 seconds viscosity and 70 per cent unsulfonatable resi- due) 5 gallons (or tank-mix oil of like specifications with 4 ounces of blood albumin spreader, 4 gallons) plus caustic soda (lye) 1 to 3 pounds, and water to make 100 gallons. The smaller amount of caustic soda is satisfactory in the interior valleys ; but in coastal regions where bark moss is prevalent a larger proportion of caustic soda is advised. Nematodes. — Nematodes are common in California, especially in some of the sandy soils. There are several types of these eelworms. Although some are beneficial, others are harmful and have done much damage in some districts. The galls they cause on the roots of various plants result in injury mainly because they interfere with the absorption of water and mineral solutes from the soil and their movement to the tops of the trees. The older almond trees seem to withstand nematode attacks fairly well, but the young trees are often killed. A resistant rootstock would be of great value in combating this pest. Clean fallowing, flooding, and growing only nematode-resistant plants before the orchard is planted, serve as means of control. Certain seedlings of several peach varieties have been found to be highly resistant to nematode attack. Even though the peach root is usually less satisfactory than the almond for heavy almond production, in nematode-infested soils it may be desirable to use these resistant rootstocks. Indian Meal Moth. — So far as is known, infestation by the Indian meal moth (Plodia interpunctella) does not take place in the field. The larvae feed on the kernels after the harvested almonds are stored. The attack usually takes place in storerooms or warehouses, which may have become infested from old grain bags kept there previously. This pest may be controlled by cleaning out the corners of the warehouse and thoroughly disinfecting the nuts with carbon disulfide (which should be kept away from fire, being explosive when in the form of a gas mixed with air) or by other means used to control insects in grain. Prevention is far easier than control in this case. Warehouses take precautions against this pest, and usually the grower need not be concerned about the matter. Grasshoppers. — Grasshoppers have been especially serious in young orchards in outlying foothill districts in some years, making it almost impossible to get trees started properly. In such locations orchards must be protected by special methods. Use of poisoned bran bait is the most effective. Pocket Gophers. 20 — Pocket gophers often girdle the trees just below 29 The paragraphs on rodents and birds were prepared by Tracy I. Storer, Zoolo- gist in the Agricultural Experiment Station. Almond Culture in California 79 the surface of the ground or cause sufficient injury to devitalize the trees. In addition, the wounds made by their gnawings frequently become in- fected with crown gall. The only safe means of control known is the con- stant use of traps supplemented at time by poisoned baits. 30 Ground Squirrels. — Large quantities of almonds are gathered by ground squirrels, generally before the nuts are sufficiently ripe to be harvested. Sometimes they take the entire crop. They may be systemati- cally controlled with strychnine-coated barley and with gas. Details as to formulas, methods, and seasons for use are well established, and are discussed in the circular cited in the preceding paragraph. Birds. — Birds, especially crows, bluejays, blackbirds, and woodpeck- ers, damage the almond orchards more than is generally believed. Lin- nets sometimes eat large numbers of fruit buds in the spring in some of the newer sections where plantings are scattered. Sapsuckers may damage indivdual trees by boring holes around the trunks of limbs, occa- sionally girdling trees by this work. In some sections crows and magpies harvest a large portion of the crop before the grower can do so — espe- cially of the soft-shelled varieties. Everyone is familiar with schemes for combating crows and other birds, such as stretching twine and ribbons across fields to frighten them, using scarecrows, and by shooting, poisoning, and trapping. The two most common means used in California are shooting and poisoning. Sometimes help is hired to travel through the orchard shooting the pests as often as opportunity permits. Use of poison involves the danger of killing beneficial and harmless species. In this state, therefore, poison is used only as a last resort, and then only under the supervision of County Agricultural Commissioners. SUMMARY OF SPRAY PROGRAMS All spraying must be done at the right time and done very thoroughly. For convenience, the spray materials to be used and the time of applica- tion for several almond diseases and insects are summarized in table 7. CROP HARVESTING AND HANDLING Handling the almond crop properly includes such processes as harvest- ing, hulling, drying, grading, bleaching, sacking, shelling, storing, and shipping. Growers are mainly concerned with harvesting, hulling, and drying, although they sometimes perform certain other operations such as shelling. Usually the factory processes and the shipping are taken 30 Storer, Tracy I. 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S o >> jo 03 a ° ,* 03 * a >- 3 03 73 la 1 | 1 Almond Culture in California 81 bD to .9 a PQ z* H a a 3 3 t3 -d O O §. s j3 bd a * ~ \^ ft ^.a § a .2 ^ s p o «Q -I J 5 ft 3 «2 o S3 g 0> 00 > g :3 li •i s B o a 2 j a t3 «? a § "3 » -a ^ 3 S s a s ■§ s s 3 J^ .2 .3 3 ^ s -a a s a § 5 © © jp » a a % I iJ Eh O ► £ *i ■ a g c ■a 1 -s ^ So «a « o c * 6J i * 3 ^ a a * "3 o J2 82 California Agricultural Extension Service [Cir. 103 care of by the California Almond Growers' Exchange (a growers' organ- ization) or by firms that buy almonds from growers. Harvesting generally begins in July, lasts through August and most of September, and in some cases even extends into October. The dates depend upon the district, the season, and the variety. Early-ripening varieties are preferable, especially where early fall rains are the rule. On the other hand, if the grower has several varieties ripening at differ- ent times, he can spread the harvest over a longer season and make better use of his labor and equipment. The approximate order of ripening of well-known varieties is given below, the earliest-ripening being placed first: Nonpareil Eureka Gilt Edge Esparto Long I.X.L. King Commercial Harriott Marie Duprey Walton Standard Drake California Klondike Golden State Languedoc I. X. L. Princess Henle Texas Jordan Silvershell California White La Maria Peerless Sultana Almendro de la P. Queen Grosse Tendre White Flat Lewelling Cover Brown XX Bigelow Batham De Witt Barclay Sellers Malaguena Reams Ne Plus Ultra Silverskin Trembath Ballard Smith XL O'Neil Bidwell The nuts in the center of the tree, being the last to ripen, may be used to indicate the proper time for harvest. The work should begin as soon as the hulls have opened to their full extent, and should be completed promptly. If gathered too early, the nuts will cling rather tenaciously and require very vigorous knocking. If, on the other hand, they are allowed to hang too long, they may be blown to the ground by light winds, and the cost of gathering be increased, as is often the case with the Peer- less ; or the hulls may dry up and cling to the nuts, increasing the expense and difficulty of hulling, as often occurs with the Nonpareil. Birds may cause serious losses, especially with the soft and paper-shell varieties. The latter, if allowed to hang too long, may often be seriously infested with worms. In damp or foggy weather, the shells turn dark and some- times mildew. Such dark nuts require heavy bleaching to brighten them for market. Knocking and Collecting the Nuts. — The crop is gathered by knocking or jarring the ripened nuts from the tree and collecting them upon sheets placed underneath. Almond varieties differ in the degree of tenacity with which they adhere to the stem when ripe. The ease of knocking also depends on the degree of maturity, the proper stage of which can be Almond Culture in California 83 learned only by experience. The Peerless is one of the easiest varieties to knock and should be harvested early to prevent the nuts being shaken off by the wind, for picking them from the ground by hand is tedious and expensive. The Texas, Languedoc, and Ne Plus Ultra also knock quite easily. The Klondike, on the other hand, is so hard to knock that the ex- pense prevents the variety from being grown commercially at a profit. Fig. 36. — Knocking almonds with poles. The California, Drake, Bidwell, and Nonpareil, though somewhat diffi- cult can be successfully knocked when at the right stage of maturity. Usually all the nuts on the tree are knocked at one operation. In some sections, however, climatic conditions may cause the nuts to mature un- evenly, and then two knockings at different times are required, as some- times happens with the Texas variety, to prevent some of the earliest- maturing nuts from falling on the ground. In certain districts the Drake variety tends to ripen unevenly. Two methods of knocking are ordinarily poling, which has long been used, and clubbing, which is rather new. In the poling method, long poles are used to strike (fig. 36) the branches with light, quick blows deliv- ered squarely near where the nuts are borne. As a glancing blow might tear the young bark and break off a great many fruit spurs, and so reduce the bearing surface for the next year, harvesters must be supervised closely. Some growers use heavy poles of pine, spruce, or fir from 1% to 2 inches in diameter at the base and from % to 1 inch at the top. Poles of this type over 20 feet long are unwieldy ; they not only swing slowly but do considerable damage. Most growers prefer 16-foot poles with a few 20- 84 California Agricultural Extension Service [Cir. 103 foot ones for use in the tops of taller trees. If the tree tops cannot be reached with these, the men climb up and use shorter poles. Some grow- ers prefer bamboo poles about 24 feet long, which, because of their light- ness, can be used with greater dexterity. Bamboo poles with short inter- nodes break less easily. Breakage may also be reduced by storing these Fig. 37. — Almond clubs: A, the original club used first in the Chico district ; B, the mallet type ; C, 1), other types of clubs. poles in a cool place where drying-out will not be excessive, by wrapping bundles of poles at night with wet burlap, and by winding each pole with tape. The second method of harvesting almonds — by jarring them loose with padded clubs — originated several years ago in the Chico district. The club was first made by wrapping and bolting a section of automobile tire around the large end of a 4-foot handle (fig. 37, A). This was used as a mallet to strike the larger limbs and jar the nuts loose. With such varie- ties as the Peerless, one man with a club could knock more almonds than several men with poles. At first clubbing was expected to cause bruises. Since, however, no injury resulted, the method has become common practice. Various firms and individuals have manufactured different types of almond clubs (fig. 37, B,C,D). Some clubs consist of a handle with a globe of rubber at the end. Another type, invented by M. J. David of Atwater, is built like a mallet, with both ends of the cross piece protected by rubber. This Almond Culture in California 85 style was thought to reach the interior branches better than the other types. Where almond clubs can be used, the expense of knocking is greatly reduced. They are most successful on the varieties that jar loose evenly. They can be used for all varieties at the proper stage of maturity, but often the clubbing must be supplemented with poling to knock off the nuts that cannot easily be jarred loose. Early in almond history the knocked nuts were picked from the ground by hand, an expensive process. Soon growers began to spread sheets Fig. 38. — Almond boat mounted on small wheels to facilitate the making of sharp turns. The boat is built so that boxes as shown can be set in its interior to receive the almonds. A buffer board on the side of the boat prevents the almonds from scattering when the sheets are dragged across the boat to dump the nuts into the boxes. The detachable buffer board fits either side of the boat. under the tree. The nuts were dumped from the sheets into boxes or bags. Almond sheets are now generally made of 7 to 12-ounce duck and range in size from 12 x 24 to 24 x 48 feet. They need not be much longer than the greatest spread of the tree. To prevent mildew and rotting of the fabric, the sheets should first be boiled in tannin solution, which greatly increases their durability. Two of these sheets are spread so that they will overlap and catch all the nuts that fall. The wear upon sheets dragged from tree to tree is considerable. To prevent this wear and to increase the speed of harvesting, growers have invented various contrivances. One of these, the widely used almond boat or sled, is sometimes built on runners, but is generally placed on 86 California Agricultural Extension Service [ Cir - 103 wheels so that sharp turns can be made. The boat consists of a long, strong, boxlike arrangement to which the sheets are attached (fig. 38). In going from tree to tree, the sheets are folded upon the boat so that they do not drag on the ground. They are pulled under the tree so the nuts can be knocked to them, as in the illustration. The sheets are pulled across the boat so as to empty the nuts into it and are then either dragged out and placed under a tree in the opposite row, or folded upon the boat, which is hauled to the next tree. When the boat is full, the nuts are shoveled into bags or boxes to be hauled to the huller later. Some almond boats (fig. 38) are built so that lug boxes or other specially made boxes can be set in rows on the bottom, and the nuts dumped directly into them. When full, the boxes are taken out of the boat and replaced with empty ones. Many growers claim that the resultant saving in handling more than repays the cost of the rather large number of boxes required. Sometimes the sheets are attached to a pole that runs along the center of the boat. With this arrangement, only half the width of the boat is available at one time for dumping the nuts ; to avoid this inconvenience the sheets should be attached near the side of the boat. If, however, they are permanently attached to one side, all the harvesting must be done from the same side, and only one row can be finished at a time. It will then be necessary to travel twice as far to harvest an orchard as if two rows could be harvested on the same trip. The harvesting of two rows at a time is especially convenient if the rows are close together so that the almond boat is near the middle when the sheets are spread. Various de- vices have been used for detaching the sheets from one side of the boat and transferring them to the other. In one of the most convenient of these, the sheets are attached to a pole, and held in place at the side of the boat by a snap at both ends. When the pole and the attached sheets are to be transferred to the other side of the boat, the snaps are unfastened and hooked on the other side. Another device, differing from the low almond boat, is a wagon box on large wheels (fig. 39) . The sheets are attached to the box, and the load- ing is accomplished just as with the boats described above. The height to which the sheets must be raised to dump the almonds, however, makes the method unhandy. Users believe that the system saves considerable expense in reloading, as the loaded wagon is hauled direct to the huller. On the other hand, to keep the labor busy in the field, this method re- quires several wagons. Another contrivance consists of sheets mounted on low wagons and held in position by a frame. This was used by N. J. Lund of Oakdale at least twenty years ago. Two wagons were necessary. Single wagons with Almond Culture in California 87 the sheets on sliding frames have pro vec^ cumbersome and less popular than the almond boats. In large orchards almond boats are commonly used. In small orchards sheets are the cheapest means, though they generally wear out in a few years. On level lands any device is possible, but on rolling lands or steep hillsides harvesting is more difficult. Boats on low runners are generally used on hillsides, and sometimes on the steepest slopes sheets alone are used. Hulling. — After being knocked and collected, the almonds, still moist, are taken to the huller. If they dry before hulling they must be sprinkled Fig. 39. — Almonds are sometimes loaded directly into the wagon box of a farm wagon. Sheets are temporarily attached for the purpose. or dipped in water to prevent breaking of the shell proper. All hulling was formerly done by hand, as in foreign countries today. Some hand hulling is still performed in our own country for very small lots, but in California such work is usually done by machinery. Although the ma- chinery is too expensive for any but the larger orchards, owners fre- quently club together and purchase a huller on the community plan. Often they haul the nuts to a custom huller where they are hulled at a stipulated price per pound, much more cheaply and rapidly than could be done by hand. Many almond hullers have been devised. Among early inventors were C. U. Reams of Suisun ; also Henry Curtner, who designed and used an almond huller at the foot of the Contra Costa hills as early as 1880. An- 88 California Agricultural Extension Service [Cie. 103 other contrivance was the Read "Sure Pop" huller, which was finally modified and sold by the Schmeiser Manufacturing Company of Davis. One of the earliest devices used and one revived from time to time con- sisted of fans that blew the nuts against a wall to knock off the hulls. Later, large machines were built with a rather elaborate system of screens, which separate the nuts from the hulls, leaves, and other matter. Fig. 40. — End view of almond-hulling machine, showing several layers of screens, together with chutes for carrying off the nuts and hulls. The nuts are shaken through the holes while the hulls pass over the screens. The nuts are separated from the hulls by being batted out, or by rubbing, or by a combination of the two methods. By means of screens (fig. 40), the nuts are separated from the hulls. Most machines pass the nuts over drapers for final hand separation to remove inferior nuts, broken pieces, and foreign substances. The amount of hand labor re- quired depends upon the machine, its adjustment, the condition of the nuts, and the completeness of the screens, conveyors, chutes, and other mechanical equipment. Some growers have improved commercial ma- chines to suit their requirements. In some instances the nuts to be hulled Almond Culture in California 89 are dumped into a large hopper from which they are automatically fed into the huller. The sticktights are returned automatically to a cracking device, so that very little hand work is necessary. Customarily, however, considerable hand labor is employed. The effectiveness of the work done by hullers depends upon the proper adjustment of the various parts and upon the condition of the nuts. The machine must be run at the correct speed and not be crowded with nuts. If it runs too fast, the almonds are broken and injured ; if too slowly, many are not hulled. If the almonds are allowed to hang on the trees too long, the hulls become dry and leathery, and the difficulty of hulling is greatly increased. In such cases, dipping the nuts in water may be beneficial. Some varieties are harder to hull than others. The Peerless, I. X. L., California, and often the Ne Plus Ultra usually hull easily. The Non- pareil, Golden State, Texas, and often the Drake are more difficult. The papershell varieties, such as the Nonpareil, are much more difficult to hull without breaking the shells than the harder-shelled varieties; greater care is therefore necessary in adjusting the machine for these. Handling Sticktights. — Often when the moisture supply in the soil is exhausted before the nuts are ripe, or when the foliage suffers from mite injury, the hulls open only slightly or not at all and in drying cling to the shells. Such sticktights can be disposed of profitably only if dried thoroughly, cracked, and sold as kernels. Drying. — Immediately after being hulled and sorted, the nuts are dried thoroughly in the sun. They are sufficiently dry when the kernels can be broken without bending. Quick drying seems essential to pre- vent excessive darkening of the shell. In the interior valleys during hot weather the nuts may be dry enough after sorting for the drying to be completed in bags. The grower must be certain that the nuts are com- pletely dry before they go to the warehouse. Generally the nuts are dried in bins, in common shallow fruit trays, or in specially constructed almond-drying trays. These trays are placed out- of-doors in direct sunlight ; and after the nuts have dried considerably, the trays are generally stacked for a time before the nuts are bagged. Bins in which almonds are dried are generally built a short distance above the ground to allow circulation of the air, and cracks are left be- tween the boards in the bottom. The nuts are shoveled into the bins to a depth of 4 inches to 1 foot or more (fig. 41). The bins are generally in direct sunlight ; and as soon as the nuts dry on top, they are turned over with a scoop shovel. This process is repeated until the nuts are uniformly and properly dried. 90 California Agricultural Extension Service [ Cir - 103 Fig. 41. — Almonds drying in wooden bins. The floors are built some distance above the ground, leaving an air space under the bins; and cracks are left be- tween the bottom boards. The almonds are turned over with a scoop shovel from time to time. Sometimes shallow trays are used instead of bins. Fig. 42. — Concrete almond-drying bins. Almond Culture in California 91 Fig. 43. — Some of the equipment used in sorting and grading shelled almonds. The nuts are fed to the moving belts from the bins located on the floor above. Inferior, damaged, and off-type nuts are removed by hand. (Courtesy California Almond Growers' Exchange.) Fig. 44. — Sorting unshelled almonds. Since the inferior nuts are removed from the best ones as they pass over the belts, a fine grade of nuts is assured. (Court- esy California Almond Growers' Exchange.) 92 California Agricultural Extension Service [Cir. 103 Another type of drying bin, made by H. G. Boyce of Winters, has been used for a number of years. This bin, with its partitions, is built of con- crete (fig. 42), which not only is durable but absorbs the sun's heat in the daytime and gives it off at night. Thus the nuts dry more or less continuously, and a bright-colored shell is obtained. Such bins are ad- vantageous in the interior valleys. Bleaching. — The trade demands a bright, golden-yellow shell. In the early days of the almond industry, when the growers bleached their own almonds, the product was not uniform. At present the Almond Growers' Exchange and various firms advise that the almonds be delivered un- bleached, for their perfected machinery for bleaching produces a more uniform product. By this method the almonds are subjected to a fine spray of water to moisten the shell and are then exposed to sulfur fumes for 10 to 30 min- utes. From 1 to 3 pounds of the best grade of flowers of sulfur is required to bleach 1 ton of almonds. Although proper bleaching does not affect the flavor in any way, overbleaching produces a sickly yellow or whitish- colored shell and also causes the kernel to deteriorate and taste soapy. Grading. — Grading standards have been developed gradually over a period of several years. The factors affecting grades were studied by the writer for the United States Department of Agriculture in cooperation with the California Almond Growers' Exchange and others, and recom- mendations to serve as a basis for grading were made in 1925. Since that time all firms handling almonds have, to a certain extent, graded for quality and size. By grading, the almonds can be separated into several classes, the appearance of each class improved, and wholesalers, retailers, and manu- facturers supplied with the proper type of nuts for their specific pur- poses (fig. 43). The result is usually an increased demand, often with higher returns to the growers, not only for the better grades, but for the poorer-appearing grades as well. By grading, the inferior nuts are sepa- rated so that they do not detract from the appearance of the high-priced nuts, and the poor grades can be placed in the proper cheaper class. Good nuts mixed with poor do not increase the price of the latter ; but, con- versely, a few poor nuts mixed with the better ones detract from the sale and lower the price of the high-grade nuts (fig. 44). Furthermore, by grading, an accurate value can be placed on each grower's almonds so that each will receive a return commensurate with his product. The California Almond Growers' Exchange calls attention 31 to the following benefits derived from grading and test-grading the grower's almonds : 31 Personal correspondence. Almond Culture in California 93 Grading concentrates the poorest-appearing material, the material of highest "meat" content, into the "Sierra" grade, which brings the largest returns when shelled. Test-grading determines how to dispose of a grower's almonds to his best interests. Some deliveries can best be sold in the shell ; others have such a high meat content that shelling is more profitable. Test-grading prevents nuts of poor quality, with stained or ragged shell, gummy or wormy meats not suitable for sale in the shell, from reaching the production grader and being mixed with nuts of good quality. Test-grading makes it possibe to ascertain what tonnage of each quality will be available for sale, as soon as the material is received at the warehouses. When shelled almonds are graded for size the confectioner's needs are better supplied and the use of more almonds is consequently encouraged. With kernels of uniform size the confectioner can produce a blanched product with less effort. The graded product, uniform in size and shape, appears more attractive. From the grower's standpoint, the so-called "test-grading" is highly important. This consists in taking a small sample from the grower's delivery and determining the percentage of the different grades of nuts composing it. The test sample must represent the whole quantity of the nuts delivered by the grower, for upon it his returns are based. It must be large enough to be representative, yet small enough to enable the test to be easily and cheaply made. To be accurate the total quantity of nuts must be mixed before the sample is taken, or several test samples must be taken from several lots. The following brief description of grading was supplied by the Cali- fornia Almond Growers' Exchange : The test of each grower's delivery starts with the drawing of a large and accurate sample by running the entire contents of several bags in each delivery through a sampling device. The representative portion thus extracted will contain the same percentage of large nuts, small nuts, and defective nuts as the grower's delivery. Exactly 10 pounds of this sample is run through a grader which separates the nuts into four grades according to size. The "Select" (first grade), "Blue Diamond" (sec- ond grade), and "Golden State" (third grade) are usually sold in the shell. The fourth or smallest grade, called the "Sierra," goes to the shelling machines. The first three grades are next examined for defective material such as stained or broken shell, which detracts from the appearance and value of the almonds and is therefore removed and termed "Poor Shell." Each of the grades is then reweighed to determine the percentage of each grade contained in the grower's delivery. A cracking test is then made on the "Sierra" and "Poor Shell" grades to determine their meat content, the basis on which the growers are paid; also on the Golden State grade, which it is sometimes more profitable to crack if the meat content is high. The delivery advance and final payment to the grower are affected by this percentage. Each grade constitutes a separate pool, and the proceeds of each pool are distributed among growers according to their tonnage in the respective pools. Confectioners frequently buy large quantities of kernels graded to their own specifications, such as width, thickness, and count per ounce. The kernels are run through machines, which, by a proper combination of circular and slot-hole screens, grade accurately to two dimensions (fig. 45). A large tonnage of meats is produced on a count-per-ounce basis, starting at 18-20 and running as small as 70-72 per 94 California Agricultural Extension Service [ Cir - 103 Fig. 45. — Mechanical grader for almond kernels. This machine has a large output and grades so accurately that the number of kernels per ounce can be guaranteed. (Courtesy California Almond Growers' Exchange.) Fig. 46. — Inspecting almond kernels. The kernels travel along on the moving apron under the magnifiers. Small pieces of shell or foreign materials are easily seen and removed. Such kernels can be guaranteed free from pieces of shell. (Courtesy California Almond Growers' Exchange.) Almond Culture in California 95 ounce. The permissible variation is very narrow; no grading is allowed to deviate more than one kernel per ounce from the correct count. Often the kernels are inspected under magnifying glasses to make certain that no shell or foreign matter is present (fig. 46). When the grower delivers shelled almonds, the testing is based upon the soundness of the kernel rather than the size. Test grading is accomplished by passing an ac- curately weighed sample through a grader which separates the flat or somewhat Fig. 47. — Equipment used for the vacuum gassing of almonds. Hand trucks loaded with bags of almonds are run into the tanks. The round doors at the ends are closed; a vacuum is obtained by pumping out the air; and the proper quantity of gas is admitted. After a certain time the air is readmitted, and the bags are removed. (Courtesy California Almond Growers' Exchange.) withered kernels from those plump and well developed. Each separation is then hand-sorted to remove the blemished kernels, pieces, and bad kernels. The various grades are (1) plump unblemished, (2) plump blemished, (3) flat unblemished, (4) flat blemished, (5) pieces, (6) bad meats. Each grade is then reweighed to deter- mine the percentage and amount of each quality in the delivery. Each grade consti- tutes a separate pool, and the grower is paid according to net returns of each pool and the quantity he may have therein. Shelling. — Within the past few years the shelled-almond trade has developed tremendously, so that the growing of superior shelling varie- ties is now important. Cracking machinery has been invented and im- proved. The California Almond Growers' Exchange and other firms have efficient machines of enormous capacity. Growers generally deliver the nuts in the shell to these firms, who do the cracking. Growers who wish, however, to shell their own almonds should remember that the drying of the kernels differs from the drying of the nuts in the shell. Kernels should 96 California Agricultural Extension Service [ Cir - 103 not be dried in the sun, which turns them dark, but should be placed in the shade and watched so that they do not become too dry. With care, fine- appearing kernels should be the result. At present one main disadvan- tage of growers' shelling their crop is the fact that they are usually un- able to produce a graded product to meet trade demands as to quality and size. Storing. — Almonds stored in warm or damp places become rancid. If properly cared for during the handling process to prevent worm infec- tion and if properly cured, they will keep satisfactorily for a year or more while awaiting removal or sale. Storage places should be uniformly cool, dry, and well ventilated. During storage, worm or weevil infestations must be prevented. Firms handling almonds in large quantities frequently destroy all worms, weevils, and eggs by treating the almonds with gases under a vacuum. This relieves the grower of trouble and expense. Sometimes the equip- ment is elaborate as well as efficient (fig. 47). Sacking. — During the preliminary handling of almonds by the grower, ordinary grain sacks are commonly used. After bleaching, when ready for market, the nuts are put in standard burlap bags about three times as large as the common grain sack. The weight of a bag of almonds de- pends not only upon the variety but also upon the year and the locality in which it is produced. The bags when filled with the varieties indicated will weigh in pounds about as follows : I. X. L., 80 ; Ne Plus Ultra, 83 ; Nonpareil, 85; Drake, 105; Texas, 110; hardshells, 130. MARKETING As previously stated, marketing, though important, is beyond the con- trol of the individual grower who must deliver his almonds to firms sell- ing them. This circular, therefore, will not discuss marketing problems, although some pertinent facts have been mentioned incidentally under various subjects. In this state the California Almond Growers' Exchange (an association of almond growers) and a number of commercial firms engage in the business of marketing almonds. 20m-3,'37