UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA CIRCULAR 357 September, 1943 ONION PRODUCTION IN CALIFORNIA 1 GLEN N. DAVIS 2 The onion is among the most widely grown vegetables in the United States. In California it has its place in every home garden, and commercial produc- tion for market is widely distributed. This, at one time (1916-17) was the greatest onion-producing state in the Union; it now ranks fourth, following Texas, New York, and Michigan. Although not a major crop from the stand- point of acreage, it is important to the California truck-crop industry, and is assuming additional importance as a source of dehydrated products. The average annual return to onion growers for the ten-year period, 1931-1940, has been approximately $1,500,000. In addition, California is among the chief onion-seed-producing areas of the world. AREAS OF PRODUCTION Tables 1, 2, and 3 present a concise picture of the areas of production and the market value of onions in California for the decade 1931 to 1940. The pro- duction of early onions is largely confined to Kern, Tulare, Riverside, and Los Angeles counties. The intermediate-crop acreage is located in the central coun- ties, whereas the late or storage crop is distributed from the northern to the southernmost part of the state. The tables reveal that after a year of high unit crop value, the acreage of onions has almost invariably increased ; and after a year of high production and low unit price, the acreage in California has almost always decreased. The fluctuation in acreage and in total production is almost as great as the fluc- tuation in market price. CULTURAL REQUIREMENTS Climate. — For best development, onions require cool weather early in the growing season, but a dry atmosphere and moderately high temperature later on. The young plants will withstand temperatures several degrees below freezing. In California the growing season is late autumn and winter, the crop maturing during the spring and summer. Proper temperature and long exposure to light are necessary for onion-bulb formation. Onions planted in the fall and winter may grow a luxuriant foliage, 1 This circular supersedes Circular 199, Onion Growing in California, by Stanley S. Rogers. 2 Assistant Professor of Truck Crops and Assistant Olericulturist in the Experiment Station. [1] 2 University of California — Experiment Station but bulbs are not formed until spring, when longer days and increased tem- peratures constitute an environment favorable to bulb formation. The early (Crystal Wax, Bermuda, San Joaquin) and intermediate varieties (Early Grano, Stockton G 36, Red 21) produce bulbs on exposure to moderate tem- peratures and relatively short periods of daylight. In contrast the late or storage types (Sweet Spanish, Australian Brown No. 5, Southport White Globe, and Yellow Globe Danvers) require relatively high temperature and exposure to long periods of daylight for bulb formation. The onions of this TABLE 1 Early-Onion Acreage and Market Values, from 1931 to 1940* County Acreage by counties, 1935-1940 1935 1936 1937 1938 1939 1940 Kern 1,250 100 300 400 1,400 100 500 800 900 100 250 400 800 50 800 50 400 Los Angeles Riverside 250 150 250 200 300 100 Total 2,050 2,800 1,650 1,250 1,300 800 State summary, 1931-1940 Year Acreage Yield per acre, 100- pound sacks Total production, sacks Value per sack Total value 1931 1932 1,250 2,450 1,150 1,850 2,050 2,850 1,650 1,250 1,300 800 135 125 145 110 107 115 155 150 205 205 169,000 306,000t 167,000 204,000 219,000 328,000t 256,000 188,000 266,000t 164.000 $1.90 1.30 1.85 1.65 2.75 0.80 1.95 1.70 0.75 $1.70 $321,000 365,000 1933 1934 1Q35 309,000 337,000 602,000 1936 1937 200,000 499,000 1938 320,000 1939 152,000 1940 $279,000 * Data from: California Cooperative Crop-Reporting Service. Vegetable crops in California. March, 1941. t Includes some quantities not harvested because of market conditions and excluded in computing total value: 1932, 25,000 sacks; 1936, 78,000 sacks; 1939, 64,000 sacks. group generally do not mature before late August or September. The varieties most commonly grown in California are discussed later under their respective group headings, and some of them are illustrated in figure 5. Soil. — A suitable soil is of fundamental importance in onion growing. For this crop the most desirable type of soil is one retentive enough under cultiva- tion to keep sufficient moisture about the roots and at the same time friable enough to be easily cultivated and to allow proper expansion of the bulbs. It should be fertile, well supplied with humus, and relatively free of weed seeds. The onion crop is grown mainly on sandy loams, silty loams, and peat. Heavy clay and coarse sand or gravel should be avoided. Moisture. — The onion is among the most shallow-rooted of the vegetable plants. During early growth it requires abundant available soil moisture near the surface. The plants will stand an excessive amount of water with less Cir. 35^ Onion Production in California injury than when the supply is deficient. New roots are not formed unless the zone from which they arise is in moist earth. The plants must be kept growing. If growth is checked temporarily by shortage of water, the outer scales seem to mature; when water is again supplied, the inner scales resume growth, causing the outer ones to split. This is one main cause of "splits" and "doubles" where onions are grown under irrigated conditions. TABLE 2 Intermediate-Onion Acreage and Market Values, from 1931 to 1940* County Acreage by counties, 1935-1940 1935 1936 1937 1938 1939 1940 100 300 280 1,600 400 70 150 200 300 1,700 500 150 100 200 300 1,500 600 100 50 100 100 1,300 200 50 50 250 200 900 100 50 Yolo 250 Kern 50 120 800 80 Tulare Total 2,750 3,000 2,800 1,800 1,500 1,350 State summary, 1931-1940 Year Acreage Yield per acre, 100- pound sacks Total production, sacks Value per sack Total value 1931 1,100 2,000 1,150 2,140 2,750 3,000 2,800 1,800 1 , 500 250 260 300 205 151 150 170 145 260 275,000 520,000f 345,000 439,000 415,000 450,000 476,000 261,000 390.000 $1.00 0.71 1.35 1.10 1.13 0.70 0.75 1.50 0.88 $275,000 1932 287,000 1933 466,000 1934 483,000 1935 469,000 1936 315,000 1937 357,000 1938 392,000 1939 343.000 1940 1, 350 2 45 33 1,000 $1.50 $496,000 * Data from : California Cooperative Crop-Reporting Service. Vegetable crops in California. March, 1941. t Includes 116,000 sacks not harvested because of market conditions; these are excluded in computing the total value. From the time the crop is beginning to mature until it is harvested, the amount of soil moisture necessary is less than during the other stages of growth. An oversupply during this period is undesirable. It may tend to make the onions watery and their keeping quality poor. FERTILIZERS The onion is an intensive crop and should yield large quantities of market- able bulbs for the area planted. Since the onion plant is shallow-rooted, a fairly high concentration of soil nutrients must be maintained in the upper foot of soil. The grower is justified in using a comparatively heavy application of fertilizer. Manure is important in growing onions on "mineral" soils — that is, those not of organic origin. Where used it should be applied to the crop preceding the onions, particularly if it is not well rotted. From 15 to 20 tons per acre 4 University of California — Experiment Station is considered sufficient. On many soils manure should be supplemented with commercial fertilizers ; or where it is not used, equally good results may be obtained with such fertilizers alone. TABLE 3 Late-Onion Acreage and Market Values, from 1931 to 1940 4 County Alameda Contra Costa... Fresno Kern Los Angeles Modoc Monterey Orange Riverside Sacramento Solano San Benito San Bernardino San Diego San Joaquin Santa Barbara . Santa Cruz Siskiyou Yolo Total Acreage by counties, 1935-1940 1935 20 150 70 1,200 250 50 400 100 700 30 50 700 230 100 650 4,700 30 100 100 150 850 20 300 50 800 100 200 50 50 1,000 100 70 30 400 4,400 20 80 200 200 600 20 300 50 500 50 150 20 50 650 200 40 20 220 3,370 1938 100 70 100 350 10 600 50 550 50 100 20 50 50 500 300 50 20 150 3,140 1939 20 200 100 500 10 450 20 1,100 50 200 20 50 50 1,150 350 50 10 250 4,580 1940 20 200 10 450 20 550 50 50 20 40 50 690 70 20 10 350 3,200 Year State summary, 1931-1940 Acreage Yield per acre, 100- pound sacks Total production, sacks Value per sack Total value 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 5,300 5,640 4,530 3,260 4,700 4,400 3,370 3,140 4,580 3,200 157 200 182 172 150 155 165 200 240 210 832,000 l,128,000t 824,000 561.000 705,000 682.000 556,000 628,000 1,099,000 672,000 $1.96 0.68 1.13 1.03 1.05 $1,631,000 591,000 931,000 578,000 740,000 580,000 612,000 754,000 659,000 $ 672,000 value. Data from : California Cooperative Crop-Reporting Service. Vegetable crops in California. March, 1941. t Includes 259,000 sacks not harvested because of market conditions; these are excluded in computing the total Peat soils do not require additional humus ; and nitrogen, phosphorus, and potash can be supplied more economically in chemical fertilizers. Experimental data as a basis for specific recommendations regarding kind and rate of application of commercial fertilizer under California conditions are indeed meager. In the light of available information, however, it is recom- mended that for the peat land of the Delta region a fertilizer be applied that will supply 100 to 180 pounds of phosphoric acid (P 2 5 ) and about 120 pounds of potash (K 2 0) per acre. An application of 1,000 pounds per acre of 0-10-12 Cir. 357] Onion Production in California fertilizer should prove satisfactory. The amount of potash depends on whether or not a fertilizer containing potash has been supplied to the soil in recent preceding years. Onions on peat soils apparently make no response to the application of nitrogen. In some places, however, nitrogen applied as a side dressing after the plants are growing, conceivably might prove beneficial. The main deciding factor is the amount of rainfall during the spring. For mineral soils the first choice is 300 pounds of ammonium sulfate per acre applied in the center of the bed at a depth of 3 to 4 inches. If this is not available 1,000 pounds per acre of a 6-10-4 or 6-9-6 fertilizer can be used. In both cases additional side dressing Fig. 1. — Double-row beds prepared for transplanting or for drilling. of 100 to 150 pounds per acre of sodium nitrate or ammonium sulfate when the onions are small, is recommended. For high yields of onions it is essential to get a good top growth before bulb formation begins. In areas where phosphorus is deficient, as in the Cuyama Valley, 600 pounds per acre of a 10-20-0 or 400 pounds of a 16-20-0 fertilizer should be used in place of a straight nitrogen fertilizer. CULTURAL METHODS Preparation of the Land. — No truck crop is more dependent on the prepara- tion of a proper seedbed than the onion. Assuming that the soil intended for planting is capable of being brought to a good mechanical condition, the first step in preparing it is to plow moderately deep, then disk, harrow, and drag until the soil is free from clods and is smooth and mellow to a depth of 5 to 7 inches. The amount of preparation required will depend upon the character of the soil, the manner of planting to be followed, and the requirements for irrigation. If manure or covercrops are to be turned under, plowing should come early enough for the material to rot thoroughly before planting time. For onions it is not necessary to turn the manure under so deeply as for most other vegetables. If the soil is well drained, and if there is no danger that surface water may accumulate, bedding the soil is not essential ; the crop may be drilled or trans- G University of California — Experiment Station planted into rows on the flat. This system is generally followed on peat soils. On most mineral soils where drainage is not sufficient and surface water may accumulate, it is a common practice to throw up beds (fig. 1) after the soil has been plowed and harrowed. As a rule the beds are 26 to 36 inches from center to center, 8 to 12 inches high. Their tops are smoothed, or "broken down," with a sled or drag before the seeding or transplanting (fig. 2) . Planting. — Two methods of planting are used in growing the commercial onion crop in California. Seeds are planted in a seedbed or nursery and later transplanted into the field, or the seeds are drilled into the soil in rows where the crop will be grown. Fig. 2. — Bear view of a machine which makes 14 single-row beds at one operation. Note the lugs on the small wheels running on the ridges; they mark the spots at which each seedling is to be transplanted. Onions belonging to the early and intermediate groups are generally grown from transplants. Seeds are planted thickly in rows which are 2 to 10 inches apart; or they may be broadcast in seedbeds and covered lightly with soil ; this should be done from 6 to 10 weeks before they are transplanted. Open beds (fig. 3) or hotbeds may be used; the former are more common. The date of planting depends on the location in the state, the variety to be planted, and the time when it is desired to have the crop mature. Such beds should be planted in September. Given seed of good quality, iy 2 to 2 pounds should produce enough plants to transplant one acre. Transplanting to the field is done between the last of November and the first of March, the exact time depending largely on the date of planting the seed and on local environmental conditions. Transplanting should be done as early as feasible, to insure abundant top growth before the start of bulb formation. When the plants are % to % inch in diameter at the surface of the soil, they should be removed to the field. Larger plants show a tendency to produce seed- stalks. A few hours before digging, the plants should be irrigated. One may dig them with a shovel or loosen them by running a cultivator knife or blade below them in such a manner that 2 or 3 inches of roots will remain attached to the CiR. 357 Onion Production in California plants. After digging, the plants should be separated from each other. The tops may be trimmed to the top of the central leaf blade, and the roots trimmed until they are % to 1 inch long. Trimming does not benefit the plant (there is even evidence that it is harmful), but it is recommended to facilitate han- dling during transplanting operations. From the time they are removed from the beds until they are transplanted, the seedlings should be covered in order to preserve as many of the small fibrous roots as possible. Actual transplanting may be done by placing the seedlings in a previously opened furrow. The roots and the base of the plant are covered by pulling the soil back into the furrow with a rake or a power-drawn lister-type cultivator Fig. 3. — Onion seedbeds. Seedlings for transplanting are grown on beds in rows planted 3 or 4 inches apart. shovel ; or they may be planted with a dibble. When a dibble is used, no furrow need be made ; a small hole is opened for each individual plant. The soil should be firmed around the root by a second stroke in which the dibble is inserted into the soil at an angle at the side of the plant. In most districts two rows are transplanted to the top of each plant bed. In some localized areas, however, such as the Coachella Valley, where the soil is extremely light or sandy and the water subirrigates laterally but a short distance from the irrigation fur- rows, low beds 12 to 18 inches from center to center are used ; a single row of transplants is arranged on top of each bed. Most of the onion crop grown for late market or storage is seeded directly into the field as early in January as possible. The soil must be finely pulverized and free from debris. Seed is usually sown at the rate of 3% to 4 pounds per acre and at a depth of % to 1 inch, according to the soil type. The deeper plant- ings are made on the lighter soils. Various types of garden seeders are used, run singly or in gangs. For plantings on previously prepared beds, two rows are drilled on the top of each bed. For plantings on the flat, the rows are 8 University of California — Experiment Station spaced 8 to 18 inches apart, the distance depending on the method of culti- vation to be used. Cultivation. — Onions are cultivated with hand implements or power-pro- pelled cultivators ; the size of the field and the spacing determine the type of machine used. As the onion is a shallow-rooted plant, too deep cultivation must be avoided lest it destroy many of the roots near the surface of the soil. In the production of onions some hand-weeding is almost always essential. In favorable seasons the handwork may be only two or three weedings ; in wet seasons more. Hand-weeding may be facilitated by certain small tools — for example the onion hoe, the hand-weeder, and the thinning or weeding hook. Fig. 4. — Side view of onion topper and grader. The capacity of this machine is 1,500 sacks per day. Irrigation. — Most of the onions produced in California require irrigation. The exact time and amount of the application are governed by the character of the soil and the season of the year. In the absence of rainfall the soil should be thoroughly irrigated before planting. Once the plants have started to grow, they must never suffer from lack of water. The number of irrigations neces- sary to maintain an adequate supply of moisture near the soil surface is largely determined by the rainfall and the season. When the plants start to mature, irrigation should be discontinued, the soil being allowed to dry out as much as possible; otherwise a second root growth may start — one that is difficult to stop and that complicates the process of properly curing the onions. HARVESTING- AND CURING When onion plants ripen properly, the leaves weaken in the region just above the bulb, and the top falls over while the leaves are still green. If the tops dry from the tips toward the base while standing erect, the neck is not closed, and the bulbs may not keep well in storage. Onions do not mature uniformly. The best time for harvest is when 15 to 25 per cent of the tops have broken over. Onions completely ripe when pulled tend to root rather easily; this type of growth is difficult to check and unfits Cir. 357] Onion Production in California 9 them for anything but immediate use. Onions pulled slightly immature seem to retain their outer skins better and are less likely to sprout and root when curing. They are, however, often less solid than when pulled fully mature. The stage at which they are harvested should be determined somewhat by whether they will be stored or placed immediately on the market. Rotting is usually the result of infection during the growth or curing of the bulbs, but infection may also follow unfavorable storage conditions. Infection and subsequent rotting may be largely prevented by rapid and complete dry- ing of the neck and outer bulb scales. In the case of soil organisms that enter through the roots and root plate, pulling the plants before the foliage has turned yellow may result in less rotting. Onions are usually loosened in the soil by running some type of blade or cutter below the bulbs. They are then pulled by hand and thrown in windrows to dry before topping. In the warm interior valley, 4 to 7 days are usually sufficient for drying, whereas more time is necessary in regions of cooler climate and higher humidity. Where the sun is hot, the tops are so laid as to protect the bulbs from sunburn — particularly with white varieties. When properly dry the tops are removed by hand, either by twisting or by cutting with a knife, shears, or power-driven mechanical toppers (fig. 4) . Immediately after topping, the bulbs are placed in sacks or slat crates and allowed to cure for a few days before being transported to market or placed in storage. Onions of the early and intermediate crops are usually marketed immediately, whereas the late varieties are often stored. STORAGE Not all onion varieties are suitable for storing. Although there might be difficulty in placing onions in the exact order of their keeping qualities by the simple water-loss method of testing, onions that have a high relative rate of water loss or a high total water loss are definitely nonkeeping types. On the other hand, those with a low relative rate of water loss or a low total water loss can be kept. Woodman and BarnelP have found that a simple test — the loss in weight from harvest in the 2 successive days of a lot of onions weighed in mass — should normally suffice to classify an onion of unknown keeping qual- ity. There is no need for actual time tests of keeping. In California most of the onion crop is marketed directly after harvest. Bulbs of the varieties comprising the early and intermediate crops do not keep well in storage even under the most favorable conditions, and would be extremely difficult to store during the hot summer months. Onions of the late or storage types should be seeded early in the spring. They mature during late September or October, when they may be stored successfully until the following March or even later if proper precautions are taken. An extensive study of the storage qualities of the principal American varie- ties of onions has been made by Magruder and co-workers. 4 Based on this study, the principal varieties are classified in the following list. 3 Woodman, E. M., and H. R. Barnell. The connection between the keeping qualities of commercial varieties of onions and the rates of water loss during storage. Annals of Applied Biology 24:219-35. 1937. 4 Magruder, Roy, and co-workers. Storage quality of the principal American varieties of onions. U. S. Dept. Agr. Cir. 618. 1941. 48 p. 10 University of California — Experiment Station Varieties Listed According to the Length of Time They Will Keep in Storage Very short Medium Italian Ked Early Yellow Globe Ebenezer Short Mountain Danvers California Early Red Ohio Yellow Globe Crystal Wax Red Wethersfield Early Grano Southport Red Globe Prizetaker Southport White Globe Yellow Bermuda White Portugal __ ■ , . Yellow Danvers Flat Short to medium Sweet Spanish Long White Sweet Spanish Australian BroAvn Red Creole White Creole Onions intended for storage should be well ripened and thoroughly dried or cured. Immature or soft onions should be sorted out, and only attractive, sound bulbs should be stored. Onions may be stored in bulk, in bins, in 50- or 100-pound sacks, or in slat crates. The bulk method, being seldom satisfactory, should not be practiced if any alternative is possible. If stored in bags they are best piled in pairs laid crosswise in stacks five or six sacks high. The stacks should be set a few inches off the floor on wooden strips, and the individual stacks separated by a few inches of space to permit air circulation. Slat crates, each holding about one bushel, are considered the most satis- factory containers for storage. Two general types of houses are employed : the so-called "common storage" and cold storage. Common storage houses are generally waterproof sheds or barns. On warm winter days the buildings should be kept closed, and the doors generally opened at night provided the weather is not too severe. Even though storage facilities are adequate there will often be more or less trouble with rot or growth, and it is sometimes necessary to sort over the onions one or more times. All onions that have started to rot should be thrown out. A few rotten onions, under moist conditions, will spoil much of the container's contents. Bulbs usually store poorly after severe mildew or thrips attacks. Cold storage, by artificial refrigeration where available, is the most satis- factory method of keeping onions over long periods. After experiments to determine the best conditions of temperature and humidity, several investi- gators agree that a temperature of 32° F with a relative humidity of 70 to 75 per cent or lower is optimum. Wright, Lauritzen, and Whiteman 5 found that bulbs sprouted least at low temperatures. Humidity had little effect on sprout- ing. It did cause, however, an increase in root formation, which bore little relation to temperature. The possible exception is the variety Sweet Spanish. If kept dry, Sweet Spanish onions store best at about 50° F. 5 Wright, Lauritzen, and Whiteman. The effects of storage temperature and humidity on the keeping quality of onions. Amer. Soe. Hort. Sci. Proc. 29 : 463. 1932. Cir. 35' Onion Production in California 11 GRADING Grading is usually done over inclined screens or slatted racks that allow loose tops and dirt to pass through. The United States grades are the only widely recognized standards ; these may be modified from time to time by Fig. 5. — Varieties of onions commonly grown in California. Reading from left to right, they are: Top row, Red 21, Crystal Wax, and Italian Red; middle row, San Joaquin, Yellow Bermuda, Stockton G 36, and Early Grano; bottom row, Yellow Sweet Spanish, Southport White Globe, and Australian Brown No. 5. rulings issued by the United States Department of Agriculture. There are two sets of grades — one for early or Bermuda onions, and one for the late crop. Copies of United States grade standards may be obtained from the Office of Shipping Point Inspection, State Department of Agriculture, Sacramento, California. Also the Bureau of Fruit and Vegetable Standardization of the 12 University of California — Experiment Station State Department of Agriculture can supply copies of the State standards as defined in the Agricultural Code of California. EARLY VARIETIES Yellow Bermuda. — Yellow Bermuda onion bulbs are medium-sized and flat (fig. 5). The skin is light straw-colored, thin, and loose. The flesh is nearly white, sweet, and mild. This variety is grown mainly in the southern part of the state for early shipment to northern markets. Crystal Wax. — Bulbs of this variety (fig. 5) are very flat, medium-sized, clear white, of mild and delicate flavor. Crystal Wax is grown for first early shipments to early markets. San Joaquin. — This variety (fig. 5) resulted from the hybridization of Stockton Yellow Globe and Early Grano. The bulbs are globe-shaped, and have an attractive yellow color. The nonbolting habit of Stockton Yellow Globe, and the mild sweet flavor of Early Grano have been incorporated into a single type. It is an extremely high-yielding variety. INTERMEDIATE VARIETIES Stockton G 36. — This variety produces large, straw-colored, semiglobe bulbs that tend to taper at top and bottom (fig. 5). It is nonbolting and is grown largely from green sets on peat or muck soils, but is also satisfactory for mineral soils. Bed 21. — This is a particularly desirable strain of California Early Red. Bed 21 matures somewhat earlier, is more uniform in size, shape, color, and time of maturity, and keeps better in storage than the older strains of this variety. The scale color is red ; the flesh is pink. The degree of color varies somewhat with the locality, being much more intense in bulbs grown along the central coast than in the interior valleys. It is thick flat in shape (fig. 5). Early Grano (Babosa) . — The bulbs of Early Grano are top-shaped (fig. 5) , medium large with dark, straw-colored skin, white flesh, and have a mild and excellent flavor. This variety is highly desirable for early markets, but it is a poor keeper. Crystal Grano. — Crystal Grano is a new variety, which is likely to become popular among growers who have a market for a white type of Early Grano. It produces a glistening white globe with white flesh, light outer scales, and mild flavor. Italian Red (Bed Torpedo). — This is an early variety (fig. 5) particularly suited for home gardens. It is very popular in Italian communities. The bulbs are long, pointed at top and bottom, large, bright, and red. The flesh is firm, sweet, and mild. ^ QR stoeage vaeieties White Sweet Spanish. — This is the largest of the white varieties of onions. The bulbs are globular, have a small neck, and are pure white in color. The flesh is clear white, firm, and mild. White Sweet Spanish bulbs are very attrac- tive, and are fair keepers. Yellow Sweet Spanish. — Bulbs of this variety are large and globular (fig. 5) with golden yellow skin and white flesh which is mild and very sweet. It is well suited for shipping and for fall storage. Southport White Globe.— The bulbs of Southport White Globe are round (fig. 5), medium-sized, solid, and pure white, with a thin and delicate skin. ClR - 357 l Onion Production in California 13 The flesh is white, and slightly tinged with pink. The bulbs have a strong flavor. This variety keeps well in storage. Yellow Globe Danvers. — This is a hardy high-yielding variety which is nsed mainly for storage. Bulbs of Yellow Globe Danvers are medium large, round, yellow, firm, and have a small neck. The flesh is white, with a slight yellow tone. Australian Brown No. 5. — This is the best strain of the standard Australian Brown variety. The bulbs are deep, flat, or semiglobular in shape (fig. 5). The scales are chestnut brown, tight-fitting, and tough. The flesh is lemon- colored and has a very strong flavor. This variety is particularly noted for its keeping quality. PRODUCTION OF DRY ONION SETS Onion sets are small bulbs produced by growing the plants under crowded conditions in the field. For small home gardens, sets are more satisfactory than raising the plants from seed. Production of onion sets is of relatively minor importance in California, the greater part of this crop being produced in the northern onion-growing states, especially near Chicago. Some onion sets are grown, however, along the south-central coastal region of California ; and this phase of the industry is apparently on the increase. For onion-set production on rich soil, 80 to 100 pounds of seed are sown to the acre ; on poorer soils, 60 to 80 pounds. The seed may be sown by hand seed drills or by gang drills of the type used for planting seed of the main onion crop. Some growers use special seeders that distribute the seed in several rows about an inch apart ; others place on the spout a funnel-shaped spreader or a wide shoe that distributes the seed over an area 3 or 4 inches wide. The distance between rows is usually 12 to 14 inches, although this may be varied to suit the individual grower. The seed must be sown thickly to prevent sets from becoming too large. If over % i ncn in diameter, they may tend to form seed- stalks — an occurrence to be avoided in the production of bulbs for market. If the sets are to be used for the growing of green bunching onions, the smaller sizes are more desirable, although the larger sets may result in a somewhat earlier crop. Onions of the flat varieties are the most satisfactory for set production ; they make globe-shaped sets that keep well in storage. Cultural requirements other than method and rate of planting are in gen- eral the same for sets as for the production of large bulbs. When mature, the sets are loosened by running a U-shaped knife under the row. They are then gathered and placed in shallow trays with lath bottoms. Topping is seldom necessary, since the small tops shrivel up and are generally broken loose by the handling and grading. The trays are left scattered a few days to dry, then stacked in the field until stored. Even at the thicker rates of planting, some of the bulbs are too large for sets and can usually be sold as "picklers" or "boilers." GREEN BUNCHING ONIONS Green bunching onions are of considerable importance in some California localities. This phase of the industry is limited to small plantings and is well suited to the general market garden. 14 University of California — Experiment Station Bunching onions may be produced from multiplier onions, dry sets, or seeds. The multiplier onion does not produce bulbs, but multiplies by giving rise to a number of side shoots at the base of the original plants. If sets or seed are planted, a white variety should be selected, since such plants make a more attractive package than a colored variety. In the marketing of this class of onions the young plants are pulled, the roots trimmed, and the outside peeled off, leaving the stem white and clean. They are then tied in small bunches, with tops trimmed slightly, and are packed in crates or baskets for transport to market. Fig. 6. — Onion-seed field in full bloom. SEED PRODUCTION California is the principal onion-seed-producing state in the Union. Quan- tities of seed are produced in Sacramento, Yolo, Contra Costa, Lake, and San Benito counties; smaller acreages in Kern, Riverside, and Butte. Mother bulbs for seed production are grown on both peat and mineral soils in the same manner as bulbs that are grown for market. Mother bulbs of the standard storage varieties are planted in California in November and Decem- ber. Bulbs of the early and intermediate crops that keep less well may be planted as early as September; seedstalks (fig. 6) are formed the following spring. Jones and Emsweller 6 found that storage, bulb size, spacing, and time of planting all had significant effects on the seed yield per acre. Although they confined their investigations to two varieties, their findings no doubt apply to onion-seed production in general. In brief they found the best temperature for the storage of mother bulbs to be between 50° and 55° F. Plants from bulbs stored at this temperature bloomed and ripened their seed earlier and pro- duced higher yields of seed than bulbs stored at higher or lower temperatures. In a comparison of eight different sizes of mother bulbs, ranging in weight from 15 to 90 grams, there was found to be an increase in seed yield per acre with each increase in size of bulb. 8 Jones, H. A., and S. L. Emsweller. Effect of storage, bulb size, spacing, and time of planting on production of onion seed. California Agr. Exp. Sta. Bui. 628 : 1-14. 1939. Cm. 357] Onion Production in California 15 In spacing tests, bulbs were set 3, 4, 6, 8, and 12 inches apart in the row ; the highest yields were obtained at the closer spacings. As the date of planting was delayed throughout the winter, there was a delay in the time of seed maturity of the late-planted bulbs ; and accompanying this was a decrease in the yield of seed. After early planting, a good root development is made during the winter, although the top growth may be small. The seedstalks appear in late February or March, and the seed heads mature in July and August. As onion seed does Fig. 7. — Harvesting onion seed. not ripen uniformly, each head must be harvested individually. At harvest, the stalk is cut by hand (fig. 7) just below the seed head. The heads are dropped into a sack suspended from the shoulders of the cutter. The sacks when full are emptied into larger sacks or into seed-tight wagon boxes. They are then hauled to large canvas sheets and spread out about 4 inches deep to dry (fig. 8). The heads should be turned daily to aid in drying. Seed is extracted with wooden rollers or by special threshing machinery. After most of the chaff has been removed by fanning or screening, the seed is washed to float off the remaining chaff and light seed. The final cleaning is by modern machinery, capable of removing all foreign matter and light seeds. According to growers, 300 pounds of seed to the acre is considered a fair yield. Yields as high as 1,500 pounds per acre have, however, been reported. DISEASES OF ONIONS 7 8 Downy Mildew, or Blight. — Onion downy mildew is caused by Peronospora destructor. The primary symptoms are spots of fine violet-tinted down upon 7 The section on diseases was prepared with the assistance of L. D. Leach, Associate Pro- fessor of Plant Pathology and Associate Pathologist in the Experiment Station. 8 For detailed information on onion diseases see : Walker, J. C. Onion diseases and their control. U. S. Dept. Agr. Farmers' Bui. 1060:1-24. 1931. 16 University of California — Experiment Station the leaves or seedstalks. Within a day or two the localized areas on the leaves become pale green and finally yellowish, the downy growth becomes more widespread, and the diseased portions of the plant eventually collapse. In the field the disease generally appears in small patches and spreads to surrounding areas. Its development is greatly aided by moist weather. In California the chief damage is to the seed crop. High humidity (condensation of dew) and low to moderate temperatures favor the mildew, which attacks the seedstalks and causes them to curl or fall over before the seed is mature. Fig. 8. — Onion seed being dried on large sheets of canvas prior to threshing. Recommended control measures include spraying with materials such as 2 per cent rosin-soap lime-sulfur, 9 bordeaux mixture, or yellow copper oxide. With the two last-mentioned materials a suitable spreading agent should be used. Leaf Mold. — A black fungus known as Macrosporium porri may attack the leaves and seedstalks in midseason or later. This weakly parasitic fungus fre- quently follows mildew, sometimes causing severe damage. The bulbs may also be attacked. Control, if needed, is the same as for downy mildew. Pinkroot. — Pinkroot is caused by a fungus, Phoms terrestris, that lives from year to year in the soil. The roots of affected plants turn pink, shrivel, and die. As the plants send out new roots, they in turn eventually become in- fected and die. As a result the plants are stunted, the bulbs small. Heavily infested soil should not be used for onions or garlic. The wide range of plants susceptible to attack by the pinkroot organism 10 limits the effectiveness of crop rotation as a means of control. The development of onion varieties resistant to pinkroot seems to present the most hopeful solution to the problem. ; ' Smith, Kalph E. Diseases of truck crops. California Agr. Ext. Cir. 119 : 1-112. "' Kreutzer, W. A. Host parasite relationships in pink rot of Allium aepae. II. The action of Phoma terrestris on Allium cepae and other roots. Phytopath. 31:907-]5. 1941. Cir. 357 j Onion Production in California 17 Neck Rot, or Botrytis Rot. — This gray feltlike growth of mold caused by a species of Botrytis appears at the neck or base of affected onions and softens and rots the tissue ; it gradually destroys the whole bulb. In late stages the rotted tissue may be covered with a black crustlike mass of fungus bodies called sclerotia. White onions are more susceptible than colored. Botrytis may also attack the leaves and the seedstalks after mildew injury. Suggested control measures include delaying the harvest until the plants are fully mature, and properly curing the bulbs after harvest. Southern Root Rot. — Southern root rot generally attacks the outer scales, producing a dry rot of the bulb tissues. In storage the infected bulbs may be completely destroyed. The fungus, Sclerotium rolfsii, may also grow up the hollow inside of the seedstalk. Here, as well as on infected bulb tissue, the fruiting bodies or sclerotia may be formed. These bodies, about the size and color of mustard seed, act as the seeds of the mold and help to spread it. Once in the soil, this root rot persists for years. Onions are moderately susceptible and cannot be planted on infested soil without danger of loss. White varie- ties are more susceptible than colored. White Rot. — White rot is caused by Sclerotium cepivorum. Affected plants die from a rotting at the neck. At this point there is a surface crust of soil, together with small, black fungus sclerotia and a thin web of white mold. Certain spots in the field covering several square yards may become infested. Onions should not be planted where this disease has appeared ; as soon as a spot is seen in the field, all the affected plants should be dug out and destroyed. Black Mold. — Black mold, caused by the fungus Aspergillus niger, fre- quently develops in spots and streaks between the outer bulb scales, usually on onions in storage. Appearance and keeping quality may be seriously in- jured. Affected bulbs should not be placed in storage. Sound bulbs if stored should be thoroughly dried. Black mold should not be confused with smut. Smut. — Smut is a disease caused by TJrocystis cepulae. The symptoms appear soon after the seedlings come above ground. Brown to black elongated blisters or pustules form within the scales or leaves, the latter usually being somewhat thickened and often curved downward. Frequently the leaf splits, exposing a powdery black mass of spores inside the blister. Where this disease occurs the soil becomes infested with smut spores, and the disease becomes worse on subsequent crops planted on the same land. Onion smut has never been found in California although it occurs elsewhere on the Pacific Coast. This disease attacks only seedling plants. After they are about 3 inches high, they become immune. Onion sets or seedlings 3 to 4 inches high grown on clean soil may be transplanted to smut-infested soil and will not contract the disease. Smut may be controlled by a formaldehyde solution applied in the furrow at planting time with a tank and drip attachment : 1 pint of commercial for- malin (37 per cent formaldehyde) to 8 gallons of water is used at the rate of 200 gallons per acre, or 1 gallon to about 185 feet of row. Smudge. — Smudge, like smut, is not known to occur in California. The causal fungus is Collet otrichum circinans. The disease is confined largely to white varieties and appears in the field just before harvest; sometimes it con- tinues to develop during storage. It is characterized by small dark-green to black dots on the outer scales. These dots may be grouped together in various 18 University of California — Experiment Station ways and are often arranged in concentric rings. Ordinarily the disease causes very little damage to the bulb, but produces a dirty, unsightly appearance that reduces their market value. Prompt harvest and storage without undue exposure to moisture are the best methods of control. Soft Rot. — Soft rot is caused by bacteria rather than fungi. The tissue first appears glassy or watersoaked and later disintegrates into a soft, watery mass, often with an offensive odor. Frequently the rot follows sunburn, freezing, and external bruises from careless handling, especially if surface wounds remain moist. It most frequently appears in storage. Control consists of care- ful handling to avoid injury and rapid drying after harvest. Yellow Dwarf. — This disease, caused by a virus, is transmitted from plant to plant by aphids. It is spread from one crop to the next by overwintering plants. It is neither seed- nor soil-borne. The symptoms are a yellow streaking followed by a general yellowing and crinkling of the leaves, which become more or less flat and droop over in the advanced stages of the disease. Flower stalks of infected seed plants are yellow, twisted, curly, and abnormally short. Such plants should be destroyed immediately. COMMON PESTS OF ONIONS 11 Red Spider. — In dry years red spiders often attack late onions. Good control is obtained by dusting with commercial dinitro dusts, 30 to 40 pounds per acre. A power or row-crop duster should be employed, and the application made before the plants are covered with webs. Onion Thrips. — This insect is among the principal pests of onions. The adults and larvae suck the plant sap from the younger leaves in the crown or growing points; the older leaves become "silvered" and later assume a with- ered or blasted appearance. These minute, winged, grayish-brown adults and pale-yellow larvae hide in the angles of the leaves ; this makes control difficult. The planting of early varieties and the use of overhead sprinkling instead of furrow irrigation or subirrigation allow the bulbs to mature with a minimum loss. In years of severe infestation and on late varieties, spraying is often necessary to save the crop : 1 part of 40 per cent nicotine sulfate to 800 parts of water, to which is added about 5 parts of liquid or powdered soap (dissolved in warm water) , should be applied at low pressure. A boom- type sprayer, like those used in weed control, is adaptable to this use. Two applications, a week or 10 days apart, are necessary, since the first application does not reach the eggs in the leaf tissue, or the pupae in the ground. Control with a poison-bait spray composed of 6*4 pounds of tartar emetic and 12% pounds of sugar to 100 gallons of water has been only partially successful on onions, though very effective against this pest on other crops. A spreader or sticker, added in amounts recommended by the manufacturer, is necessary to insure satis- factory deposit. Onion Maggot. — In the spring, particularly in wet seasons, small, white maggots often attack sets and small bulbs. Clean culture and destruction of onion refuse after harvest are important in keeping down the infestation. The most effective chemical control is mercuric chloride, 12 1 ounce to 8 gallons of 11 The section on insects was prepared by S. F. Bailey, Assistant Professor of Entomology and Assistant Entomologist in the Experiment Station. 12 Mercuric chloride is a deadly poison and must be handled with care. It corrodes metals, consequently it must be handled in pottery, glass, or other resistant containers. Gir. 357] Onion Production in California 19 water. This solution may be applied with a watering can — about % pint to each plant. The number of applications will be determined by the severity of the infestation, the first treatment being 3 or 4 days after transplanting, the second 9 or 10 days after transplanting, and the third about 10 days later. Other Pests. — Planting should be avoided on land known to be infested with nematodes or heavily infested with wireworms. The soil fumigants sometimes used for these pests are expensive and give only partial control. 20w-9, '43(6554)