UNIVERSITY OF CALIFORNIA 
 
 COLLEGE OF AGRICULTURE 
 
 AGRICULTURAL EXPERIMENT STATION 
 
 BERKELEY, CALIFORNIA 
 
 CIRCULAR No. 285 
 
 SWEET POTATO PRODUCTION 
 IN CALIFORNIA 
 
 BY 
 
 J. T. EOSA 
 
 FOKEWOBD 
 
 The sweet potato is one of the leading truck crops of the United 
 States, but at the present time it is only of minor importance in Cali- 
 fornia. In 1922, the year of heaviest production, there was grown in 
 the United States 1,117,000 acres of sweet potatoes, producing 
 109,394,000 bushels. The crop provided approximately 55 pounds of 
 sweet potatoes per capita for the entire population of the United 
 States. In the same year the acreage of sweet potatoes in the states 
 west of the Rocky Mountains was : California 8000, Arizona 2000 and 
 New Mexico 1000, a total of 11,000 acres, producing 1,292,000 bushels. 
 Therefore, for the seven and one-half million people living in the eight 
 states west of the Rockies, there was produced in this district only 
 about 10 pounds of sweet potatoes per capita. This small production 
 in the western states as compared with that of the country as a whole 
 has resulted in a low per capita consumption of sweet potatoes and 
 their shipment from the southern and middle western states to the 
 Pacific coast markets. Thus, in 1923, Los Angeles received 41 cars of 
 sweet potatoes from Californian points, 35 cars from Arkansas, and 9 
 cars from other states. The sweet potatoes supplied to western markets 
 are often rather poor in quality and inadequate for the market 
 demands. The retail price, moreover? is too high to encourage large 
 consumption, except during that brief portion of the year when the 
 crop is being harvested and most growers are hurrying their product 
 to market. 
 
 On the other hand, returns to the grower have not always been 
 satisfactory because much of the crop is sold during the temporary 
 
Z UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 over-supply of the markets at digging time in the fall. The 1922 crop 
 was an example of such a condition. Prices during the fall were so 
 low that the crop of some fields was not dug at all — yet by the following 
 February the wholesale price had risen to 5 cents a pound for the 
 properly cured storage house product. Adequate storage facilities 
 would make it possible to market at more satisfactory prices many 
 more sweet potatoes than are now grown in California. Adequate 
 storage facilities would tend to eliminate such uneconomical practices 
 as shipping sweet potatoes from Arkansas, Tennessee, and other dis- 
 tant regions, to Pacific coast markets. The usual seasonal variation in 
 prices of sweet potatoes is indicated by figures 1 and 2. 
 
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 Fig. 1. — Seasonal range in jobbing prices on Jersey and Nancy Hall sweet 
 potatoes at San Francisco, 1922-1923. 
 
 Factors that must be considered if yields, production, demand and 
 consumption of sweet potatoes are to.be increased, are disease control, 
 and the production of varieties or types that are more popular with 
 the consumer. Two diseases commonly known as stem rot and black 
 rot in many cases are destroying 10 to 50 per cent of the crop. Both 
 are controllable to a large extent by well proven methods. Varieties 
 of the sweet, moist-fleshed type, such as Nancy Hall and Porto Rico 
 Yam, are not only more productive and better for storage than the 
 dry meally Jersey type now so generally grown, but are preferred by 
 many consumers. 
 
Croc. 285] 
 
 SWEET POTATO PRODUCTION IN CALIFORNIA 
 
 It is the purpose of this circular to give such information regarding 
 sweet potatoes as is available and applicable to California conditions, 
 and as is thought necessary to increase the yield and the market 
 demand. 
 
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 Fig. 2. — Seasonal range, jobbing prices on sweet potatoes, 
 San Francisco, 1923-1924. 
 
 REQUIREMENTS FOE GEOWING SWEET POTATOES 
 
 Soils. — Areas for commercial sweet potato production are limited 
 by the special soil requirements for growing this crop, especially under 
 irrigated conditions. Generally, light sandy loam and coarse sandy 
 soils are most suitable. Fresno Sand and Oakley Sand are the soil 
 types most used for sweet potatoes. The fertility necessary as com- 
 pared with that required by other crops is not very high. Yet some 
 of the sandy soils on which sweet potatoes are now grown, would 
 probably produce larger crops if organic matter and commercial 
 fertilizers were added. The physical texture of the soil seems to 
 
4 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 affect both the form, size, and smoothness of the potatoes. On the 
 heavier soils, the top growth is likely to be so excessive as to retard 
 maturity and cause inconvenience in digging. One advantage of sandy 
 soils is that they retain less of the irrigating water than do heavy 
 soils. The plants grown on sandy soils, therefore, suffer less from 
 excessive moisture. There is a considerable range in the soil adapta- 
 tion of different varieties. The Jersey type, especially, requires sandy 
 soils, while the Nancy Hall, Porto Rico, and some of the large white 
 varieties will develop satisfactorily on medium-heavy loam soils. 
 
 Climate. — The sweet potato requires a long warm growing season. 
 The plants are very sensitive to frost and therefore cannot be set in 
 the open field until danger of frost is over. Since the tops are also 
 killed by the first heavy frost in the fall, the crop should be dug before 
 or soon after the first frost. The normal development of the plant is 
 retarded by cool cloudy weather during the growing season, and regions 
 having cold nights during the summer are not favorable. Hence, 
 sweet potatoes are grown in California only at some distance from 
 the coast, except south of Los Angeles. 
 
 Moisture. — While the sweet potato plant probably uses as much 
 water as any other crop having the same amount of foliage and grown 
 under the same conditions, the fact remains that the plant is not 
 injured seriously by rather long periods of drought. This has led to 
 the idea that sweet potatoes are a drought-resistant crop. Excellent 
 crops have been grown in the Turlock district, on sandy land, without 
 irrigation, but such soils are usually sub-irrigated to some extent from 
 nearby canals. Good growth and yields have been observed where 
 by mid-summer there was no available soil moisture nearer than 20 
 inches to 2 feet from the surface. On higher lands which are not sub- 
 irrigated, regular surface irrigation by the furrow method is practiced. 
 
 SWEET POTATO DISTEICTS 
 
 The larger portion of the sweet potato acreage of California is 
 located in Merced and Stanislaus counties in the extensive area of 
 sandy soils adjoining the main line of the Southern Pacific railway. 
 Both soil and climate are very favorable for maximum yields of sweet 
 potatoes of good quality. Smaller sweet potato districts are located 
 in Los Angeles County, in the San Fernando and San Gabriel valleys, 
 and in Orange and San Diego counties. Sweet potatoes have also 
 been grown successfully in the upper part of the Sacramento Valley, 
 at Redding ; in Kern County, at Bakersfield and Shafter ; in southwest 
 Fresno County, and to a small extent in the Imperial Valley near 
 Yuma. 
 
ClRC. 285] SWEET POTATO PRODUCTION IN CALIFORNIA 
 
 GEOWING THE PLANTS 
 
 Sweet potatoes are usually propagated by means of plants produced 
 from small potatoes placed in a hotbed, with proper moisture and 
 temperature conditions. The sweet potato itself consists of a root, 
 originally a fibrous feeding root, which in process of development has 
 thickened for a greater or less distance from the central stem. On 
 each such thickened root, or potato, are found four rows of lateral 
 fibrous feeding roots, which usually disappear before the crop matures, 
 so that only the slight depressions where these roots were attached can 
 be seen. From the neighborhood of these root scars, adventitious buds 
 originate, and under favorable growing conditions, sprouts are formed. 
 These sprouts have an independent root system and are only weakly 
 connected with the mother potato, from which, however, they derive 
 most of their food up to transplanting time. The sweet potato root 
 has no true rest period, for the sprouts may start growing at any time 
 moisture and temperature conditions are suitable. This often occurs 
 in the storage house in the early part of the storage season, also 
 in the field before harvest, when the partly developed roots are 
 separated from the main stem by diseases. 
 
 The potatoes used for propagating are called "seed" or "seed 
 stock." The smaller potatoes ranging from one to two inches in 
 diameter are most suitable for this purpose. Larger potatoes may 
 be used, but they are more expensive and do not produce so many 
 plants from a given quantity of seed stock. Where it is necessary 
 to use large potatoes, the yield of plants can be increased by splitting 
 the potatoes lengthwise, and bedding with the flat side down. The 
 selection of sweet potato seed is discussed in detail at the end of this 
 circular. Growers in the Turlock district allow about 400 pounds 
 of seed for each acre to be planted. From 10,000 to 14,000 plants to 
 the acre are required, depending on the distance of planting. If there 
 is no disease, the seed disinfected, the hotbed properly prepared and 
 carefully handled, 200 pounds of seed should produce enough plants 
 for one acre. 
 
 Preparation of the Hotbed. — The bed for growing sweet potato 
 plants is usually heated with fresh stable manure. It should be located 
 in a warm, sunny, well-drained spot, and protected from north winds, 
 by a fence or windbreak. A trench is dug 6 to 8 feet wide and 15 
 inches deep, and as long as necessary to accommodate the quantity of 
 seed to be bedded. When plants for a large acreage are grown, it is 
 best to arrange the plant beds in short sections parallel to each other. 
 Several days before the sweet potatoes are bedded, the trench should 
 
UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 be filled with fresh heating horse manure which is first packed by 
 tramping", then covered with a layer of 3 to 4 inches of sandy soil or 
 sand. On this the seed potatoes are laid about one-half inch apart, 
 when the bed has become warm. The seed should be covered at once 
 to a depth of three inches. The best material for covering is clean 
 sand, preferably taken from a creek bed or sand pit where con- 
 tamination by sweet potato diseases is unlikely. As the plants or 
 "sprouts" can obtain all the necessary nutriment for their develop- 
 ment from the mother seed potato, there is no need for a fertile soil 
 
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 f\ue. Space. 
 
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 f7oor. 
 
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 furnace 
 
 Fig. 3. — Fire-heated hotbed. Above is shown cross-section of the bed. The 
 flue-space extends the entire width and length of the bed and is covered with 
 rough flooring. Over this is a layer of tamped soil or clay from 3 to 6 inches 
 deep, above which is the sand in which the potatoes are bedded. 
 
 Below is shown a side-section, showing arrangement of furnace and flue. 
 
 in the plant bed. Furthermore, sand does not bake and crust in such 
 a way as to prevent the sprouts emerging, as heavier soils often do. 
 Also the formation of fibrous roots on the plants is much more extensive 
 when grown in sand, than in heavier soils. The last is an important 
 factor, especially with varieties such as the Nancy Hall, which form 
 fibrous roots sparingly and are therefore more difficult to transplant 
 successfully. Plants grown in sand are also pulled up more easily 
 and with less damage to the root system. Another advantage of using 
 
Circ. 285] 
 
 SWEET POTATO PRODUCTION IN CALIFORNIA 
 
 clean sand in the preparation of the sweet potato plant bed is the 
 avoidance of diseases, especially black rot and stem rot, which are 
 likely to be harbored in soils taken from the cultivated fields, or which 
 have been used for sweet potato beds in previous years. 
 
 Other Types of Hotbeds. — Because of the increasing difficulty of 
 obtaining sufficient quantities of fresh stable manure for the prepara- 
 tion of large plant beds each year, other methods of heating the beds 
 may have to be resorted to. The flue-heated bed, one type of which 
 is shown in fig. 3, is well suited for growing sweet potato plants. A pit 
 
 Fig. 4. — Top view of fire-heated hotbed, concrete construction. (Courtesy 
 New Jersey Experiment Station.) 
 
 is located at one end of the bed. Recessed beneath the bed, and open- 
 ing into this pit, is a brick furnace, which may be equipped with a 
 grate for burning coal or briquettes. The smoke, fumes, and heat 
 from the firebox are conducted beneath the plant bed, either through 
 tile flues spaced 3 feet apart and entering a chimney at the far end 
 through a header ; or the hotbed may have a tight floor, with an open 
 space beneath, extending for its entire width and length and connected 
 with a chimney at the far end. Heaters of either of the above types 
 may accommodate beds 8 to 12 feet wide and 40 feet long. For larger 
 beds, it may be more economical to use coils of pipe for steam or hot 
 water heating. 
 
8 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 In the cooler sections, sweet potato beds are enclosed by a frame 
 of 1 by 12 inch boards and covered with glazed sash or medium weight 
 unbleached muslin cloth, water-proofed by treatment with hot raw 
 linseed oil. In the warmer sections, including the Turlock district 
 and the lower San Joaquin Valley, the beds are seldom enclosed, but 
 are covered with board shutters 3 to 4 feet wide and slightly longer 
 than the bed is wide. These shutters are placed on the surface of the 
 beds at bedding time, to retain the heat in the bed. m After the bed has 
 once warmed up, there is danger of over-heating, and the shutters are 
 removed from time to time to regulate the temperature. When the 
 plants begin to push through, the shutters are permanently removed. 
 A thermometer should be placed near the center of the hotbed, and the 
 temperature kept around 80° F. until the sprouts have started. 
 
 SEED TEEATMENT 
 
 One of the most important steps in the control of sweet potato 
 diseases is disinfection of the seed potatoes before bedding. This is 
 especially important in the control of black rot, both in the hotbed 
 and after transplanting to the field. It is also helpful in controlling 
 other diseases. It should be remembered that seed treatment is only 
 one step in the control of sweet potato diseases, and will not be very 
 effective unless the other precautions for disease prevention — seed 
 selection, clean hotbed soils, and rotation of crops — are also observed. 
 Seed treatment is intended to destroy the disease organisms on the 
 surface of apparently sound healthy seed. Under the influence of the 
 warmth and moisture of the hotbed these organisms grow and attack 
 the young sprouts. Many of the plants are often killed in this way 
 in the hotbed before transplanting, and many others are infected 
 and die later in the field, reducing the stand, and lessening the yield. 
 
 The standard method of disinfecting seed sweet potatoes is by 
 dipping the seed for 10 minutes in a solution made up at the rate of 
 one ounce of corrosive sublimate (Bichloride of mercury or Mercuric 
 chloride) to 8 gallons of water. The corrosive sublimate should be 
 dissolved beforehand in a gallon of hot water, to which may be added 
 one pound of common table or bulk salt to hasten the process. Fairly 
 rapid solution can be obtained even in cold water with this mixture 
 of the corrosive sublimate and table salt. 
 
 It is usually convenient to dip lots of from 60 to 75 pounds of seed 
 at a time, using a 50- or 60-gallon wooden barrel containing 32 gallons 
 of the solution. Dipping the seed for longer than 10 minutes is likely 
 to cause injury. 
 
ClRC. 285] SWEET POTATO PRODUCTION IN CALIFORNIA 9 
 
 As the corrosive sublimate reacts quickly with any sort of metal, 
 the solution should be prepared and handled only in wooden, stoneware, 
 glass or enameled containers. As it is also deadly poison to all animal 
 life the powder and the solution must be kept out of reach of children 
 and stock. 
 
 The solution of corrosive sublimate is weakened by dipping the 
 seed potatoes. Gunny sacks should not be used for containers in dip- 
 ping the seed because the jute fibre from which they are made absorbs 
 large amounts of the chemical from the solution. Wooden baskets or 
 cotton sacks may .be used, or the seed may be dumped into the solution 
 loose. The last is the best practice if the barrel or dipping vat is 
 located on an elevated platform, and is provided with a large drain 
 plug so that the solution can be promptly drained off into another 
 barrel at the end of each treatment. 
 
 To keep the solution up to the original strength, a small amount of 
 corrosive sublimate should be added occasionally. It has been found 
 by experiments that the addition of one-half ounce for every 100 
 pounds of seed treated, together with enough water to restore the 
 original volume, will keep the strength of the solution about constant. 
 If the solution is used over four times without addition of more cor- 
 rosive sublimate it becomes so weak that the treatment is not effective. 
 If a stock solution of 4 ounces to the gallon has been prepared, one pint 
 of this should be added for every 100 pounds of seed dipped. 
 
 The seed potatoes, upon removal from the solution, should be 
 allowed to drain a minute or two, then placed directly in the hotbed, 
 without rinsing. 
 
 TRANSPLANTING 
 
 The transplanting of the plants from the hotbed to the field should 
 begin as soon as danger of frost is over, and the preparation of the 
 hotbed should consequently be timed so that the first crop of plants is 
 ready for transplanting about the time the weather becomes warm 
 enough for field setting. In the Los Angeles district, transplanting 
 usually begins about April 1 and continues until the first part of June. 
 In the San Joaquin Valley, transplanting begins the latter part of 
 April and continues until late in June. Objections to late planting 
 are that it is difficult to secure a good stand because of the heat, and 
 that the shorter growing season reduces the yield. It is the general 
 experience of growers in California that the earlier transplantings 
 produce the larger crop. Some experiments in Kern County, con- 
 ducted by W. B. Camp in 1923, strikingly demonstrate the decrease 
 in yield from late plantings. The test included Southern Queen, Nancy 
 
10 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 Hall, Dooley, Porto Kico, and Big Stem Jersey, the results with all 
 being similar to those given below for the Jersey variety. 
 
 Date Transplanted Besults — Dug October 21 
 
 May 21 Good yield. Large uniform potatoes, nearly all marketable. 
 
 June 9 Fair yield, many medium size potatoes, 30 per cent small. 
 
 June 25 Light yield, nearly all small potatoes. 
 
 July 11 Light yield, all small potatoes. 
 
 In pulling the plants for transplanting, the mother or "seed 
 potato" is held in place with one hand and the plants are pulled up 
 with the other. Plants more than 10 inches high should be pruned 
 by cutting off the tops of the bundles of plants with a large knife. 
 After pulling, the plants should be kept out of the sun until trans- 
 planted. The roots especially should be kept from drying out. Sweet 
 potato plants may be held for several days after pulling or may be 
 shipped long distances, if the roots are kept slightly moist, by wrapping 
 in moistened newspaper. The tops must be kept dry, otherwise slimy 
 decay takes place within a day or two. 
 
 Most of the commercial acreage of sweet potatoes is set with horse- 
 drawn transplanting machines, of which there are several types on the 
 market. These machines are equipped with a tank and an automatic 
 device which discharges a small amount of water at the roots of each 
 plant as it is set. Even though the soil seems moist at transplanting 
 time, it is best to use the watering attachment. On very sandy soils, 
 which dry out quickly, and when transplanting late in spring, it is best 
 to give a row irrigation within a day or two to moisten the ridges and 
 give the young plants a favorable start before they have become dry. 
 
 Propagation by Vine Cuttings. — In the southern states it is custom- 
 ary to grow a late crop from vine cuttings or "slips" taken from the 
 tops of the early crop, which is always grown from plants propagated 
 in hotbeds. The cuttings of the sweet potato take root readily when 
 severed from the parent plant and transplanted to a new location 
 under favorable conditions. Koots form very quickly from the nodes. 
 The cuttings may be from 10 to 30 inches long, but the shorter 
 cuttings are much more conveniently handled when transplanted by 
 machine. Propagation by cuttings does not seem to be generally 
 advisable in California because of the difficulty of getting a stand in 
 mid-summer, and the small yield produced by late plantings. Propa- 
 gating in this way, however, may be desirable for one reason : namely, 
 the production of potatoes free from disease especially for seed pur- 
 poses. One of the worst diseases, stem rot, is spread from year to year 
 within the seed potatoes. The disease works within the stem of the 
 
ClRC. 285] SWEET POTATO PRODUCTION IN CALIFORNIA 11 
 
 plant, from the root upward. However, cuttings taken from the tips 
 of vines that appear to be healthy, early in the season, are very likely 
 to be free of disease, and if transplanted to a field where the soil is also 
 free from sweet potato diseases will produce healthy potatoes. This 
 method then results in production of seed that is nearly disease-free, 
 and may be expected to produce healthy plants if bedded under proper 
 conditions the next spring. "Slip seed" grown on nematode-free soil 
 is also the only way to make certain of nematode-free seed. 
 
 This practice is known in the South as "slip seeding" and is of 
 importance in controlling disease, if other precautions are also 
 observed. A very satisfactory crop of seed was grown at Delhi. 
 California, in 1924, by this method. 
 
 CULTUEAL PEACTICES 
 
 The exact details of culture for sweet potatoes vary in different 
 localities. A few general suggestions, however, may be useful to the 
 prospective grower who has had no experience with this crop. 
 
 Sweet potatoes are nearly always planted on ridges from 8 to 15 
 inches high, the lower ridges being generally preferred. Kidge-culture 
 provides more favorable conditions for the development of the roots, 
 facilitates row irrigation and reduces the labor of harvesting as com- 
 pared to flat culture. The rows are generally marked off 3 feet apart, 
 and the ridges formed with a lister. The riding disc cultivator can 
 also be used to form ridges after removing all but the two inner discs 
 and setting these at the proper angle to form a ridge between them. 
 The tops of the ridges are smoothed slightly with a plank drag before 
 setting plants, if a transplanting machine is used. 
 
 The spacing of plants in the row should be varied to suit conditions. 
 Varieties that tend to make excessively large potatoes, especially the 
 Nancy Hall, should be set much closer than varieties that tend to pro- 
 duce a larger number of medium-sized potatoes, such as the various 
 strains of the Jersey type. On the more fertile soils all varieties should 
 be spaced closer than on poorer soils. The average distance between 
 plants in the row is 15 inches. This may be shortened to 10 inches, or 
 lengthened to 18 inches, according to the variety and soil fertility. 
 
 When the young plants begin to send out runners, it is necessary 
 to turn these so that they will grow along the ridge and not interfere 
 with cultivation between the rows. This vine turning is usually per- 
 formed by hand, but some of the growers equip their cultivators with 
 rods to lift the vines out of the way. If the tips of the vines are 
 covered with soil during cultivation they are likely to take root and 
 
12 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 form small potatoes which detract from the development of the potatoes 
 in the main hill. Eventually the vines cover the space between the 
 rows and cultivation is discontinued, though irrigation may be 
 continued as late as September 1 on late plantings. 
 
 Most of the sweet potatoes in California have hitherto been grown 
 on sub-irrigated land in the Stanislaus-Merced district with the water 
 table 4 to 5 feet below the surface during the growing season. With the 
 lining of the canals to prevent seepage and the pumping being carried 
 on in some districts to lower the water table, it will probably become 
 necessary to resort to surface irrigation. The crop can be grown very 
 successfully with surface irrigation (by the furrow method) but the 
 cost is greater than under sub-irrigated conditions. Where sweet 
 potatoes are to be surface-irrigated, the land should be carefully graded 
 and the water handled so as to get as even a distribution as possible. 
 During the dry season of 1924 many fields received emergency irriga- 
 tions and it was found that in those portions of the fields where too 
 much water was received the potatoes were over-sized and rough, and 
 many of them cracked. 
 
 Even more important is the relation of soil moisture to disease. 
 During 1924, the portions of the fields that were rather dry or that 
 received only a moderate amount of water were fairly free from the 
 black rot disease. In the lower and excessively moist portions of the 
 fields a very large proportion of the potatoes were affected with black 
 rot. Careful and uniform distributions of water will do much to 
 lessen the losses caused by this disease. 
 
 On sub-irrigated land two surface irrigations are usually given 
 shortly after transplanting. On the higher lands, about seven irriga- 
 tions during the growing season are required. 
 
 HARVESTING 
 
 The time of harvesting depends on market conditions and the 
 maturity of the crop. Sweet potatoes planted out in May will con- 
 tinue growing until the tops are frosted in November. The rate of 
 growth of the potatoes themselves has not been determined for Cali- 
 fornia conditions, but the increase in yield for the last few weeks of 
 growth is probably not very great at least for early planted potatoes. 
 On the other hand, there is a period in the middle of the season when 
 the increase in size of the potatoes is very rapid. 
 
 Harvesting begins in August in central California, and slightly 
 earlier in southern California. The first sweet potatoes from Imperial 
 Valley, reach market about July 15. Even the earliest plantings are 
 
Cmc. 285] 
 
 SWEET POTATO PRODUCTION IN CALIFORNIA 
 
 13 
 
 not nearly full grown when harvesting begins, but the high price 
 received for the earliest potatoes compensates for the smaller yield. 
 Harvesting increases in volume through September and October. Prac- 
 tically all of the sweet potatoes dug before the middle of October are 
 sold on local markets or shipped at once. Those intended for storage 
 are harvested from the middle of October until after the tops have 
 been frosted. The effect of the freezing of the tops on the quality of 
 the roots is a much disputed question, though it is generally believed 
 that unless the tops are cut off the day after the first killing frost the 
 
 Fig. 5. — Vine cutter, drawn by one horse, used in stripping sweet potato 
 vines in Virginia. (Courtesy Virignia Truck Experiment Station.) 
 
 potatoes will not keep well in storage. Certainly the effect of tem- 
 perature low enough to freeze the tips of the potatoes themselves, either 
 before or after digging, is disastrous. 
 
 In harvesting, the first step is to dispose of the tops. Most of the 
 California growers now do this by hand, using long curved knives to 
 cut them from the central stem. They are then removed and piled in 
 convenient places to be used later in covering the heaps of potatoes. 
 Recently the value of the tops as stock feed has been realized, and 
 many of them are taken from the fields by the dairymen for feeding to 
 their cattle. The tops may also be clipped from the main stem with a 
 hoe, and left between the rows so that they will be buried in plowing 
 out the potatoes. In some eastern districts the slow laborious task of 
 cutting the tops by hand is avoided by the use of a horse-drawn "vine 
 cutter, ' ' such as that shown in fig. 5. 
 
14 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 After the tops are cut and removed from the ridges, the roots are 
 plowed out. A 14-inch mold-board plow may be used for this purpose. 
 Most growers, however, have plows with specially adapted mold-boards 
 for this work. One grower, Mr. J. B. Steele of Baldwin Park, Cali- 
 fornia, has adapted an old Irish potato digger for harvesting sweet 
 potatoes, by removing the elevator apron and welding on an extra wide 
 and heavy point. The ordinary potato digger has not proved success- 
 ful with sweet potatoes because of the large amount of power required 
 and the excessive bruising of the potatoes. After plowing out, the 
 crop should be gathered promptly. In the San Joaquin Valley the 
 practice is to leave the potatoes attached to the central stem and gather 
 the crop into large piles at convenient intervals through the field. 
 These piles are covered with sweet potato tops to protect them from the 
 sun and from light frosts that are likely to occur late in the fall. As a 
 rule, the potatoes are sorted from the piles and packed in shipping 
 crates the day they are dug. This practice is probably the most con- 
 venient and economical where the potatoes are being dug for immediate 
 shipment. However, the covered piles may be left in the field for 
 several days. The over-sized, the cracked, the small or seed-sized, the 
 stringy potatoes and the stem are left on the ground to be gathered up 
 later. This practice makes it impossible to select healthy seed — a 
 thing that is best done in the field at the time of digging. When the 
 potatoes have been snapped from the stems, it is impossible to tell 
 which have come from healthy plants, and which from diseased plants. 
 The safest plan is to inspect the individual hills immediately after 
 plowing out, choosing those which show potatoes of desirable type, and 
 which prove to be healthy upon splitting the central stem. The smaller 
 sized potatoes, still attached to the stem, may then be gathered and 
 saved for seed purposes. A few careful growers have been successful 
 in selecting healthy seed from the piles, however, by inspecting the 
 stem of each intact hill and laying aside the " seed-size" potatoes at 
 the time the No. 1 potatoes are packed. 
 
 In harvesting sweet potatoes it is essential to avoid all rough 
 handling that tends to bruise them. The skin is very tender when the 
 potatoes are dug, and it is easily broken or rubbed off. Where the 
 flesh is exposed in this way, the molds that cause rotting are likely to 
 gain entrance and even if rot does not occur, a sunken discolored spot 
 is caused that injures the appearance. All unnecessary handling 
 should be avoided especially for potatoes that are to go into storage. 
 Storage stock should be placed in lug boxes without piling, hauled 
 directly to the storage house, and emptied into storage bins at once. 
 
ClRC. 285] SWEET POTATO PRODUCTION IN CALIFORNIA 15 
 
 PACKING 
 
 For many years, the standard container for California-grown sweet 
 potatoes was the 100-pound crate. Experience has shown, however, 
 that this is too large and heavy for the best results in shipping, and 
 in recent years most of the crop has been packed in "Special" or 
 "three-quarter" crates which hold 75 to 80 pounds as packed in the 
 field. The inside dimensions of this crate are 9% by 14 by 22% inches. 
 In packing the crate is first nearly filled and then a top layer of 
 uniform-sized potatoes is carefully arranged so as to give a good bulge 
 to the cover when nailed on. The pressure from this bulge holds the 
 potatoes firm, thus preventing movement in the crate, and lessening the 
 injury to the appearance of the potatoes in a slack pack. 
 
 The U. S. Standard Grade for No. 1 sweet potatoes calls for potatoes 
 not less than 1% inches and not over 3% inches in diameter. These 
 size requirements are rather carefully observed by California growers. 
 The over-sized "Jumbo" potatoes as well as the cracked, cut, or other- 
 wise imperfect potatoes are usually not marketable, except as stock 
 feed. It is estimated that when barley is worth $50 a ton, sweet 
 potatoes are worth $15 as feed for dairy cattle. The sizes below No. 1 
 grade are utilized for canner stock and for seed. For canning, long 
 potatoes from % to 1% inches in diameter are demanded. Somewhat 
 smaller potatoes serve as well or better for seed. The "strings" also 
 have some value as feed for hogs. 
 
 VAEIETIES 
 
 Of the many varieties of sweet potatoes grown in the United States, 
 only a few are important in California. From the marketing stand- 
 point, this is fortunate, for when a district specializes on one or two 
 varieties of a crop it is easier to put out a standardized product and to 
 build up an established reputation for it. Still, the leading varieties 
 differ enough in their adaptability to different soils and localities, 
 suitability for market purposes and other characteristics, to justify the 
 grower in considering carefully the varietal question. Below are 
 discussed some of the main points connected with varieties now grown 
 or likely to be grown in California. 
 
 The Jersey Type. — There are several distinct strains of this general 
 type, which together comprise most of the commercial acreage. One 
 strain has been grown in this state for many years, and is generally 
 spoken of as the "Old California." It appears to be distinct from 
 any of the Eastern strains. The potatoes are long and slender, there 
 
16 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 
 
 are a large number to the plant, and under unfavorable growing con- 
 ditions many of them do not reach sufficient thickness for the market 
 grade. Generally, this strain produces a larger proportion of canner 
 and seed stock than any other variety or strain grown. Its vines are 
 rather slender with small leaves of variable type, some being narrow 
 and pointed, some distinctly forked or three-lobed, and others broadly 
 triangular. Another strain, grown extensively in recent years, is 
 generally referred to as the "New Jersey" strain, seed having been 
 imported from that state about 1921. This is the same as the Eastern 
 variety, Little Stem, or Up River. It can scarcely be distinguished 
 from the California strain by the appearance of the leaves or runners ; 
 the potatoes, however, are much shorter and thicker, more chunky or 
 short-spindle shaped than the California. This strain has become 
 very popular, as it produces a large yield with a high percentage of 
 No. 1 potatoes. A third strain is the Bed Jersey, quite similar to the 
 New Jersey strain in every respect except the intense red color of the 
 skin. It has no special qualities to commend it and is not in demand on 
 the markets. 
 
 The Jersey strains in general produce well on very sandy soil, but 
 perhaps are the least adapted of all varieties, to the heavier soils. This 
 type of sweet potato has a dry mealy flesh, which is preferred by some 
 people. At present it is the most popular variety for summer and 
 fall use on the Pacific coast markets, but generally sells at a lower 
 price than other varieties during the winter. The various strains of 
 this type are rather early in maturing. The small light growth of top 
 and the fact that potatoes adhere to the central stem more strongly 
 than other varieties, are advantages in harvesting. In storage-quality, 
 the Jersey type is decidedly inferior to other varieties even under the 
 best conditions, the potatoes usually beginning to shrivel at the stem 
 end about a month after being placed in storage. This defect in the 
 Jersey type is more noticeable in California than in the East. Because 
 of its poor keeping quality and the market preference for other sorts 
 in winter, it is not advisable to store the Jersey type in commercial 
 quantities for more than a few weeks. 
 
 Nancy Hall. — This variety has recently been grown in California in 
 commercial quantities and is justly increasing in favor. The potatoes 
 are medium-long, spindle-shaped, tapering at both ends, smooth and 
 uniform when grown under favorable conditions. The skin is light 
 pink of uneven density. The flesh is pink while raw, becoming golden 
 yellow and very sweet and juicy when cooked. Many prefer this type 
 when they once become acquainted with it. Varieties like the Nancy 
 Hall having moist sweet flesh are often spoken of as "Yams" though 
 
ClRC. 285] SWEET POTATO PRODUCTION IN CALIFORNIA 17 
 
 the true Yam is a tropical plant belonging to another botanical family, 
 and is not grown in the United States. The Xancy Hall is early and 
 very productive. It is one of the best keeping varieties, and therefore 
 well suited for storage. While best adapted to the sandy soils, this 
 variety thrives well enough on moderately heavy soils to make a satis- 
 factory crop for home use. On account of the rapid early growth of 
 the potatoes and of their tendency to grow too large, this variety can 
 be dug for the extra early crop when only half grown, yet produce 
 satisfactory yields. Objections to this variety are : its tendency to 
 grow potatoes that are too large or rough ; susceptibility to Stem Rot 
 disease ; and difficulty in obtaining a good stand of plants in the field, 
 on account of small number of roots formed by the sprouts before 
 transplanting from the hotbed. The tendency to over-sized roots can 
 be corrected by setting the plants close in the row. Spacing the plants 
 as close as 6 inches in the row has been found to give maximum yields 
 on moist fertile soils. 
 
 Porto Rico. — This variety is of somewhat the same general type 
 as the Nancy Hall; but is considered superior in some respects. The 
 potatoes are of a deep coppery red and have a deep pink flesh, which is 
 richly colored and very sweet and juicy when cooked. The potatoes 
 are rather irregular, though most of them are spindle-shaped, and 
 of medium length. This variety has been very successfully grown in 
 the Los Angeles district for several years and in 1924 several small 
 patches grown at Turlock and Delhi proved its adaptability to the 
 San Joaquin Valley. Though this variety is practically unknown on 
 the markets of northern California and the Northwestern states, its 
 fine qualities will soon render it popular in these sections. It is not 
 particularly early, but is well suited for the main fall shipping crop 
 and for winter storage. 
 
 Southern Queen, — This is a large coarse-growing variety, having 
 white skin and cream-colored flesh. Though not in demand on the 
 markets, because of the white color, it is of fairly good eating quality 
 after it has been in storage for several months. This variety is hardly 
 grown at all in California. It is known in the Turlock district as 
 the "Tennessee." 
 
 STOEAGE 
 
 The sweet potato is commonly regarded as a difficult crop to store 
 over winter, because of its sensitiveness to cold and susceptibility to 
 rots caused by fungi when the storage conditions are defective. How- 
 ever, during the past ten years very satisfactory and dependable 
 methods for sweet potato storage have been worked out, largely by the 
 U. S. Department of Agriculture, and thousands of the modern storage 
 
18 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 
 
 houses have been erected in the southern and eastern states. California 
 growers have been very slow to provide suitable storage facilities for 
 sweet potatoes. There is only one large storage house and two small 
 houses of more or less modern type in the state. On account of the mild 
 climate, California growers have been fairly successful in storing sweet 
 potatoes in cellars in some years. However, conditions in these cellars 
 are seldom well regulated and the losses by decay and shrinkage are 
 generally very heavy, a total loss being a common occurrence in cold 
 or wet seasons. The inferior quality of cellar stock as compared to 
 1 ' cured, " or the storage house stock, is reflected in the much lower 
 prices paid for the former. Data from the San Francisco market 
 reports bear out this statement. 
 
 The great advantage of storing sweet potatoes is that it greatly 
 extends the marketing season and the period for consuming the crop. 
 Instead of forcing the entire crop onto the market during the digging 
 season, from August to November, a large part may be held in storage 
 for marketing during the winter and early spring. Sweet potatoes can 
 easily be kept as late as May 1. Thus the length of the sweet potato 
 season may be doubled. Unlike many vegetables, sweet potato con- 
 sumption is not seasonal. If available, they are used as extensively in 
 winter as in autumn. Development of more and better storage facili- 
 ties will provide an outlet for much larger crops of sweet potatoes 
 than have ever been grown in California. 
 
 The sweet potato requires a warm, dry, well ventilated storage place 
 if it is to be kept through the winter with minimum loss from shrinkage 
 and decay. An important factor is a preliminary "curing" or sweat- 
 ing process, given for the first 10 to 14 days after the potatoes go into 
 storage. During this period the temperature should be held at 80° 
 to 85° F., and the ventilators kept open so that excess moisture can 
 pass off from the potatoes freely. Some chemical changes occur in 
 the potatoes themselves during this curing process : the skins become 
 tougher and thicker, and the cut and bruised places seal over so that 
 rot-producing fungi cannot gain entrance. After curing, the storage 
 rooms should be held at 50° to 55° F., with the ventilators opened or 
 closed according to temperature and moisture conditions outdoors. The 
 necessary conditions for curing and holding sweet potatoes through 
 the winter can best be supplied in specially constructed sweet potato 
 houses. These houses do not have to be so substantially constructed 
 in California as they do in eastern states, and need not be expensive. 
 Persons interested in commercial storage of sweet potatoes are advised 
 to secure Farmers' Bulletin No. 970 from the U. S. Department of 
 Agriculture, Washington, D. C. 
 
Cmc. 285] 
 
 SWEET POTATO PRODUCTION IN CALIFORNIA 
 
 19 
 
 Fig. 6. — Showing dead plants and missing places in sweet potato field, just 
 before harvest. Due to black rot, chiefly. 
 
 Fig. 7. — Healthy field of sweet potatoes with practically no missing places. 
 Seed were carefully selected and dipped in Corrosive Sublimate solution. Nancy 
 Hall variety on left, Jerseys on right. A. R. Vierra, Turlock, California. 
 
20 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 DISEASES 
 
 The sweet potato is subject to several destructive diseases, affecting 
 both the plant and the potato, and to some diseases which attack the 
 potato only. These diseases have been increasing in severity in recent 
 years. Some of them are prevalent at the present time, and are the 
 cause of great loss to the growers who often are not aware of them. 
 The control of disease is the chief problem now confronting California 
 growers, from the standpoint of production. 
 
 During the summer of 1923 and 1924 many fields in the main 
 sweet potato districts were visited by the writer. In most cases some 
 disease was present, and in some fields 40 to 50 per cent of the plants 
 were dead or dying of disease. There can be little profit with such a 
 large reduction in the stand. It costs as much to plant, cultivate, and 
 irrigate a field with only half a stand of plants as with a full stand. 
 Losses of plants of only 10 or 15 per cent, which may not even be 
 noticed by the grower, will reduce the yield in nearly the same ratio, 
 which in years of low prices may entirely prevent all profit. Losses 
 of plants just after transplanting are often attributed by growers to 
 causes other than disease, while death of plants during the growing 
 season often passes unnoticed. The chief diseases are so widely spread 
 and may cause such heavy losses that the simple specific measures for 
 preventing them should always be followed, whether or not the growers 
 know them to be present. 
 
 The two diseases which cause most loss in California, commonly 
 known as stem rot and black rot, are prevalent in other parts of the 
 country also, and their control has been carefully worked out. For- 
 tunately, investigations carried out in 1923 and 1924 by Dr. J. L. 
 Weimar of the U. S. Department of Agriculture, in cooperation with 
 the Farm Advisors of Stanislaus, Merced, Los Angeles, and Orange 
 counties, demonstrated that the same control measures that have proved 
 so effective in the eastern states will also control these diseases in 
 California. The chief diseases are briefly described below and on the 
 last page is given a summary of the methods of control. 
 
 Black Rot. — This disease is caused by a fungus which attacks the 
 underground part of the stem as well as the potatoes. Decayed spots 
 of varying size appear upon the potatoes. These spots are black on 
 the surface and somewhat sunken. The decay often starts in growth 
 cracks or in places wounded by gophers; while in storage, cuts and 
 bruises are the chief starting points. The decay is not very deep and 
 if cut away the sound flesh below turns a greenish color soon after 
 
ClRC. 285] SWEET POTATO PRODUCTION IN CALIFORNIA 
 
 21 
 
 Fig. 8. — Selecting seed from cull-pile in the field. The wrong way to 
 
 get healthy seed. 
 
 -The right way to select seed sweet potatoes. The hills are laid 
 out and stem of each one is examined for disease. 
 
22 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 exposure to air. The flesh just below the decayed spots is very bitter 
 and when potatoes affected with black rot are cooked the bitterness 
 permeates the whole potato. This disease is often found on seed stock 
 in the spring as black patches on the sides, or as a dry, shriveled and 
 blackened condition at the stem end of the potato. On the plant, infec- 
 tion by Black Rot may be first noted at the time the plants are pulled 
 in the hotbed for transplanting. At this stage the stem is black and 
 decayed for a short distance from its basal end. Such plants die soon 
 if transplanted to the field, although sometimes when conditions are not 
 favorable for the development of the disease, they may grow and 
 produce several potatoes which are likely to be diseased. Many plants 
 
 
 Fig. 10. — Black rot on sweet potato, showing surface decay. (U.S.D.A.) 
 
 that do not show infection when pulled for transplanting may really 
 be infected and die after transplanting. Infected plants which do not 
 die in the early part of the season, may be recognized at harvest time 
 by the dry black decay of the lower part of the central stem. Such 
 plants usually produce only a few small potatoes. 
 
 The black rot fungus attacks no plant but sweet potatoes, yet it 
 may survive in the soil over winter and even for several years. Rota- 
 tion of crops is therefore a necessity as a part of any method of control. 
 But if the soil is free from disease to begin with and all the other 
 measures to prevent infection are observed, several crops of sweet 
 potatoes may be grown in succession on the same land. The most 
 important cause of infection is the use of infected seed. If potatoes 
 showing black rot are bedded in the plant .bed, the fungus grows 
 from the mother potato and attacks the new plants. Even seed 
 potatoes that appear to be healthy, generally have a plentiful supply 
 of the fungus on their surface, if they have been stored in bins with 
 
Circ. 285] 
 
 SWEET POTATO PRODUCTION IN CALIFORNIA 
 
 23 
 
 infected potatoes. However, healthy plants may be grown from seed 
 of this kind if it is disinfected before bedding according to the direc- 
 tions given on page 8, and bedded in a disease-free hotbed. The seed 
 potatoes that have visible signs of Black Rot should be sorted out at 
 bedding time and destroyed as they cannot be disinfected. 
 
 Another source of infection is the soil of the plant bed. On many 
 farms there is only one spot that is sunny, sheltered from wind and 
 accessible to water. The tendency is to make the sweet potato plant 
 bed in this one favored spot year after year. When plant pulling is 
 
 Fig. 11. — Black rot on sweet potato plants, upon removal from hotbed. 
 
 (U.SJD.A.) 
 
 finished in the spring, the old beds are left without further attention 
 until bedding time the next spring. By this time the soil in and around 
 the beds is likely to be saturated with the fungous organisms that 
 cause black rot and other diseases, which have spread from the decay- 
 ing seed potatoes of the previous year. In fact, many growers prefer 
 to make their plant beds on the same spot as in previous years because 
 of the improvement in physical texture of the soil through the incor- 
 poration of the decayed seed, plants and manure of previous years. 
 The result is a plant bed soil thoroughly infected with diseases which 
 infects each new crop of plants in turn. There are three remedies for 
 this situation. One is to make the plant beds in a fresh spot each 
 year — but this is not always possible. Another is to sterilize the soil 
 
24 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 before preparing the plant bed each spring. Drenching the soil with a 
 solution of formaldehyde (one pint to 30 gallons of water) at the rate 
 of one gallon to each square foot of surface would probably disinfect 
 old hotbed soils so that they could be used again. Generally, however, 
 the most /practical method is to make the plant bed with fresh soil or 
 sand hauled from a place where contamination by sweet potato disease 
 is not likely, such as a dry creek bed. With a layer of this soil or 
 sand 3 or 4 inches deep below the seed potatoes, and a covering of the 
 same material, the chances of infection reaching the plants from with- 
 out are slight. 
 
 Stem Rot. — This disease, like black rot, is caused by a fungus that 
 may live in the soil for several years. It attacks both the potatoes and 
 the stems, but differs from black rot in that it develops entirely within 
 the tissues, being seldom visible from the exterior until the plant dies. 
 Potatoes borne by diseased plants usually contain the disease, and as 
 they are likely to be small and therefore used for seed purposes, they 
 are one of the chief causes of the spread of the disease from year to 
 year. In advanced stages, potatoes affected with stem rot show a 
 blackened ring just below the skin, but so many in less advanced 
 stages do not show this ring that healthy seed cannot be secured by 
 discarding those that do not show this discoloration. The only way to 
 secure absolutely healthy seed is to select them from healthy plants at 
 digging time. Each hill should be inspected by splitting the central 
 stem. If the interior is brownish in color, the plant is infected with 
 stem rot, and the potatoes it bears are not suitable for seed. This 
 disease also occurs on the young plants in the hotbed, the leaves becom- 
 ing yellowish and the underground part of the stem bluish in color. 
 These plants generally die before or soon after transplanting. One 
 of the commonest causes of poor stands in the fields is the early death 
 of a large number of plants that became diseased in the hotbed. When 
 the soil of the field contains this disease more plants become infected 
 during the growing season. Such plants are distinguished by their 
 yellowish or brown leaves, and by the blackened dead vines. They often 
 have formed several potatoes, and after the disease kills the central 
 stem these potatoes send up sprouts similar to those ordinarily pro- 
 duced in the hotbed. The typical appearance of plants thus affected is 
 shown in fig. 13. Other plants affected still later may show no sign 
 of disease until the stems are split during seed inspection at digging 
 time. 
 
Cmc. 285] SWEET POTATO PRODUCTION IN CALIFORNIA 
 
 25 
 
 B 
 
 Fig. 12. — Stem rot of sweet potato, showing the discoloration of 
 vascular tissue. (U.S.D.A.) 
 
 Fig. 13. — Stem rot often affects plants as shown in the center — the vines 
 have died and sprouts have grown out from the little potatoes already formed. 
 
26 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 '■-<, 
 
 Fig. 14. — Soft rot, showing the luxuriant growth of the fungus on the 
 surface, which often occurs in storage. (U.S.D.A.) 
 
Cmc.285] 
 
 SWEET POTATO PRODUCTION IN CALIFORNIA 
 
 27 
 
 Scurf. — This disease is caused by a fungus that occurs in many 
 soils, even where sweet potatoes have never been grown. It is most 
 likely to affect potatoes on soils which are heavy or very moist. It 
 causes small black spots on the skin which in severe cases run together, 
 giving the potatoes a splotched or stained appearance. These diseased 
 areas are superficial, seldom extending deeper than the skin, and doing 
 no damage aside from producing their unsightly appearance. The 
 disease is prevented to a large extent by the same methods as those 
 given for black rot. 
 
 Fig. 15. — King rot of sweet potato — caused by same fungus as soft rot. 
 
 (U.S.D.A.) 
 
 Soft Rot. — This disease occurs to a small extent in the field, but 
 does its main damage during storage. It is caused by one of the most 
 common molds, spores of which are in the soil and floating in the air 
 everywhere. Fortunately, this mold is unable to penetrate the normal 
 healthy skin, being able to enter the potato only through cuts and 
 bruises. Hence, careful handling of storage stock lessens the chances 
 of decay. Curing the sweet potatoes in warm dry houses just after 
 digging increases their resistance to this decay, while cold, damp 
 storage, as well as handling or sorting while in storage, greatly 
 increases the chances of its occurrence. The same organism often 
 produces a dry brownish decay known as ring rot. This usually 
 
28 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 affects only portions of the tuber while soft rot renders the whole 
 tuber mushy. 
 
 Nematodes. — Nematode injury, usually called root knot, occurs on 
 sweet potatoes to some extent, but the injury to this crop is not so 
 severe as it is to tomatoes, melons, and other garden vegetables. In 
 fact, very satisfactory crops of sweet potatoes can be grown on soils 
 so thoroughly infested with nematodes that it is impossible to grow 
 most of the common vegetables and fruits. Nematode injury appears 
 as small galls on the fibrous roots of the sweet potato plant, and as 
 larger galls on the root end of the potatoes. Nematodes are easily 
 spread from place to place by sweet potato plants; therefore, unless 
 one is absolutely sure that the plants are free of nematodes, sweet 
 potatoes should not be grown in young orchards on sandy land where 
 nematode infestation would have serious and permanent results. 
 Nematodes are most serious on light sandy soils. It is said that they 
 can be starved out by growing crops immune to nematodes for two 
 years. All cereal crops and the Iron. and Brabham varieties of cow 
 peas are immune. 
 
 THE DISEASE CONTEOL PEOGEAMME 
 
 The grower of sweet potatoes when once he realizes the losses caused 
 by the common diseases, will wish to control not only one, but all of 
 them, especially as he may not know which one of the diseases is doing 
 the damage. Fortunately, the control of each of the common diseases 
 requires practically the same treatments. No one treatment will be 
 effective against any disease, hence, it is necessary to follow a pro- 
 gramme of several distinct steps. 
 
 1. In the fall, healthy seed should be selected from healthy plants. 
 The stems of the plants are split at digging time, and seed saved only 
 from plants that show no internal discoloration. This selected seed 
 should be kept separate from other potatoes in storage to avoid the 
 possibility of infection. It should be stored in new boxes, or in old 
 boxes that have been disinfected with bluestone solution (1 pound to 
 25 gallons of water). 
 
 2. Just before bedding time in the spring, the seed stock should 
 be sorted over. All potatoes showing black rot or other decay must 
 be discarded. 
 
 3. Make the hotbed in a new place each year or use fresh soil or 
 sand in preparing it. 
 
CIRC. 285] SWEET POTATO PRODUCTION IN CALIFORNIA 29 
 
 4. Do not let decayed potatoes become mixed with the soil or the 
 manure used in making the hotbed, and do not leave them lying about 
 near the bed. 
 
 5. Disinfect the seed before bedding, by dipping it for 10 minutes 
 in a solution of corrosive sublimate ( 4 ounces to 32 gallons of water). 
 See page 8 for details. 
 
 6. Discard all plants that show any evidence of disease when pull- 
 ing for transplanting, especially those showing black or bluish dis- 
 coloration on the basal portion of the stem. 
 
 7. Grow sweet potatoes wherever possible on land that has not been 
 used for this crop in several years. 
 
 8. Try to grow healthy seed and healthy plants at home rather 
 than buy them from some other section where diseases are likely to 
 be just as common. 
 
STATION PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION 
 
 BULLETINS 
 
 No. No. 
 
 253. Irrigation and Soil Conditions in the 352. 
 
 Sierra Nevada Foothills, California. 
 
 261. Melaxuma of the Walnut, "Juglans 353. 
 
 regia." 354. 
 
 262. Citrus Diseases of Florida and Cuba 357. 
 
 Compared with Those of California. 
 
 263. Size Grades for Ripe Olives. 
 
 268. Growing and Grafting Olive Seedlings. 358. 
 
 273. Preliminary Report on Kearney Vine- 
 yard Experimental Drain. 359. 
 
 275. The Cultivation of Belladonna in Cali- 361. 
 
 fornia. 
 
 276. The Pomegranate. 362. 
 
 277. Sudan Grass 363. 
 
 278. Grain Sorghums. 
 
 279. Irrigation of Rice in California. 364. 
 
 280. Irrigation of Alfalfa in the Sacramento 
 
 Valley. 366. 
 
 283. The Olive Insects of California. 
 
 285. The Milk Goat in California. 367. 
 
 286. Commercial Fertilizers. 
 
 294. Bean Culture in California. 368. 
 
 304. A Study of the Effects of Freezes on 
 
 Citrus in California. 369. 
 
 310. Plum Pollination. 370. 
 
 312. Mariout Barley. 371. 
 
 313. Pruning Young Deciduous Fruit Trees. 
 
 319. Caprifigs and Caprification. 372. 
 
 324. Storage of Perishable Fruit at Freezing 
 
 Temperatures. 374. 
 
 325. Rice Irrigation Measurements and Ex- 
 
 periments in Sacramento Valley, 
 1914-1919. 375. 
 
 328. Prune Growing in California. 
 
 331. Phylloxera-Resistant Stocks. 376. 
 
 334. Preliminary Volume Tables for Second- 
 
 Growth Redwood. 377. 
 
 335. Cocoanut Meal as a Feed for Dairy 379. 
 
 Cows and Other Livestock. 380. 
 
 339. The Relative Cost of Making Logs from 
 
 Small and Large Timber. 381. 
 
 340. Control of the Pocket Gopher in Cali- 
 
 fornia. 382. 
 
 343. Cheese Pests and Their Control. 
 
 344. Cold Storage as an Aid to the Market- 383. 
 
 ing of Plums. 
 
 346. Almond Pollination. 384. 
 
 347. The Control of Red Spiders in Decidu- 
 
 ous Orchards. 
 
 348. Pruning Young Olive Trees. 385. 
 
 349. A Study of Sidedraft and Tractor 386. 
 
 Hitches. 
 
 350. Agriculture in Cut-over Redwood Lands. 387. 
 
 Further Experiments in Plum Pollina- 
 tion. 
 
 Bovine Infectious Abortion. 
 
 Results of Rice Experiments in 1922. 
 
 A Self-mixing Dusting Machine for 
 Applying Dry Insecticides and 
 Fungicides. 
 
 Black Measles, Water Berries, and 
 Related Vine Troubles. 
 
 Fruit Beverage Investigations. 
 
 Preliminary Yield Tables for Second 
 Growth Redwood. 
 
 Dust and the Tractor Engine. 
 
 The Pruning of Citrus Trees in Cali- 
 fornia. 
 
 Fungicidal Dusts for the Control of 
 Bunt. 
 
 Turkish Tobacco Culture, Curing and 
 Marketing. 
 
 Methods of Harvesting and Irrigation 
 in Relation to Mouldy Walnuts. 
 
 Bacterial Decomposition of Olives dur- 
 ing Pickling. 
 
 Comparison of Woods for Butter Boxes. 
 
 Browning of Yellow Newtown Apples. 
 
 The Relative Cost of Yarding Small 
 and Large Timber. 
 
 The Cost of Producing Market Milk and 
 Butterfat on 246 California Dairies. 
 
 A Survey of Orchard Practices in the 
 Citrus Industry of Southern Cali- 
 fornia. 
 
 Results of Rice Experiments at Cor- 
 tena, 1923. 
 
 Sun-Drying and Dehydration of Wal- 
 nuts. 
 
 The Cold Storage of Pears. 
 
 Walnut Culture in California. 
 
 Growth of Eucalyptus in California 
 Plantations. 
 
 Growing and Handling Asparagus 
 Crowns. 
 
 Pumping for Drainage in the San 
 Joaquin Valley, California. 
 
 Monilia Blossom Blight (Brown Rot) 
 of Apricot. 
 
 A Study of the Relative Values of Cer- 
 tain Succulent Feeds and Alfalfa Meal 
 as Sourses of Vitamin A for Poultry. 
 
 Pollination of the Sweet Cherry. 
 
 Pruning Bearing Deciduous Fruit 
 Trees. 
 
 Fig Smut. 
 
 CIRCULARS 
 
 No. 
 
 Alfalfa. 
 
 Correspondence Courses in Agriculture. 
 
 The Selection and Cost of a Small 
 Pumping Plant. 
 
 House Fumigation. 
 
 The Control of Citrus Insects. 
 136. Melilotus indica as a Green-Manure 
 Crop for California. 
 
 Oidium or Powdery Mildew of the Vine. 
 
 Feeding and Management of Hogs. 
 
 Some Observations on the Bulk Hand- 
 ling of Grain in California. 
 
 Irrigation Practice in Growing Small 
 Fruit in California. 
 
 87. 
 113. 
 117. 
 
 127. 
 129. 
 
 144. 
 151. 
 152. 
 
 154. 
 
 No. 
 
 155. Bovine Tuberculosis. 
 
 157. Control of the Pear Scab. 
 
 160. Lettuce Growing in California. 
 
 161. Potatoes in California. 
 
 164. Small Fruit Culture in California. 
 
 165. Fundamentals of Sugar Beet Culture 
 
 under California Conditions. 
 
 166. The County Farm Bureau. 
 
 167. Feeding Stuffs of Minor Importance. 
 170. Fertilizing California Soils for the 1918 
 
 Crop. 
 173. The Construction of the Wood-Hoop 
 
 Silo. 
 178. The Packing of Apples in California. 
 
CIRCULARS — (Continued) 
 
 No. 
 
 179. Factors of Importance in Producing 
 
 Milk of Low Bacterial Count. 
 184. A Flock of Sheep on the Farm. 
 190. Agriculture Clubs in California. 
 199. Onion Growing in California. 
 
 202. County Organizations for Rural Fire 
 
 Control. 
 
 203. Peat as a Manure Substitute. 
 
 208. Summary of the Annual Reports of the 
 
 Farm Advisors of California. 
 
 209. The Function of the Farm Bureau. _ 
 
 210. Suggestions 'to the Settler in California. 
 212. Salvaging Rain-Damaged Prunes. 
 
 214. Seed Treatment for the Prevention of 
 
 Cereal Smuts. 
 
 215. Feeding Dairy Cows in California. 
 217. Methods for Marketing Vegetables in 
 
 California. 
 220. Unfermented Fruit Juices. 
 228. Vineyard Irrigation in Arid Climates. 
 
 231. The Home Vineyard. 
 
 232. Harvesting and Handling California 
 
 Cherries for Eastern Shipment. 
 
 233. Artificial Incubation. 
 
 234. Winter Injury to Young Walnut Trees 
 
 during 1921-22. 
 
 235. Soil Analysis and Soil and Plant Inter- 
 relations. 
 
 236. The Common Hawks and Owls of Cali- 
 
 fornia from the Standpoint of the 
 Rancher. 
 
 237. Directions for the Tanning and Dress- 
 
 of Furs. 
 
 238. The Apricot in California. 
 
 239. Harvesting and Handling Apricots and 
 
 Plums for Eastern Shipment. 
 
 240. Harvesting and Handling Pears for 
 
 Eastern Shipment. 
 
 241. Harvesting and Handling Peaches for 
 
 Eastern Shipment. 
 
 243. Marmalade Juice and Jelly Juice from 
 
 Citrus Fruits. 
 
 244. Central Wire Bracing for Fruit Trees. 
 
 245. Vine Pruning Systems. 
 
 247. Colonization and Rural Development. 
 
 248. Some Common Errors in Vine Pruning 
 
 and Their Remedies. 
 
 249. Replacing Missing Vines. 
 
 250. Measurement of Irrigation Water on 
 
 the Farm. 
 
 No. 
 
 251. Recommendations Concerning the Com- 
 
 mon Diseases and Parasites of 
 Poultry in California. 
 
 252. Supports for Vines. 
 
 253. Vineyard Plans. 
 
 254. The Use of Artificial Light to Increase 
 
 Winter Egg Production. 
 
 255. Leguminous Plants as Organic Fertil- 
 
 izer in California Agriculture. 
 
 256. The Control of Wild Morning Glory. 
 
 257. The Small-Seeded Horse Bean. 
 
 258. Thinning Deciduous Fruits. 
 
 259. Pear By-products. 
 
 260. A Selected List of References Relating 
 
 to Irrigation in California. 
 
 261. Sewing Grain Sacks. 
 
 262. Cabbage Growing in California. 
 
 263. Tomato Production in California. 
 
 264. Preliminary Essentials to Bovine Tuber- 
 
 culosis Control. 
 
 265. Plant Disease and Pest Control. 
 
 266. Analyzing the Citrus Orchard by Means 
 
 of Simple Tree Records. 
 
 267. The Tendency of Tractors to Rise in 
 
 Front; Causes and Remedies. 
 
 268. Inexpensive Lavor-saving Poultry Ap- 
 
 pliances. 
 
 269. An Orchard Brush Burner. 
 
 270. A Farm Septic Tank. 
 
 271. Brooding Chicks Artificially. 
 
 272. California Farm Tenancy and Methods 
 
 of Leasing. 
 
 273. Saving the Gophered Citrus Tree. 
 
 275. Marketable California Decorative 
 
 Greens. 
 
 276. Home Canning. 
 
 277. Head, Cane, and Cordon Pruning of 
 
 Vines. 
 
 278. Olive Pickling in Mediterranean Coun- 
 
 tries. 
 
 279. The Preparation and Refining of Olive 
 
 Oil in Southern Europe. 
 
 281. The Results of a Survey to Determine 
 
 the Cost of Producing Beef in Cali- 
 fornia. 
 
 282. Prevention of Insect Attack on Stored 
 
 Grain. 
 
 283. Fertilizing Citrus Trees in California. 
 
 284. The Almond in California. 
 
 The publications listed above may be had by addressing 
 
 College of Agriculture, 
 
 University of California, 
 
 Berkeley, California. 
 
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