i**Tv '**hi*? Division of Agricultural Sciences UNIVERSITY OF CALIFORNIA QUALITY SWEET CORN PRODUCTION W. L. Sims • R. F. Kasmire • O. A. Lorenz CALIFORNIA AGRICULTURAL Experiment Station Extension Service CIRCULAR 557 CORN ON THE COB A summer favorite on dinner tables, corn is one of our most perishable vegetables. Without help sweet corn harvested at its prime starts to lose quality as soon as it is picked. The growers greatest problem, therefore is getting ears to the local market in prime eating condition. This circular describes field practices and discusses harvest- ing, packing, and cooling methods that will greatly help preserve quality. Suitable vari- eties and principal marketing districts are discussed, and important pests and their control are touched upon. THE AUTHORS: William L. Sims is Agriculturist, Agricultural Extension Service, Davis; Robert F. Kasmire is Agriculturist, Agricultural Extension Service, Davis; Oscar A. Lorenz is Olericulturist in the Experiment Station, Davis. JUNE, 1971 This circular replaces circular 515, Sweet Corn Production in California, by J. H. MacGillivray, W. L. Sims, and R. F. Kasmire, and draws in part on that publication. [2] QUALITY SWEET CORN PRODUCTION Sweet corn is a warm-season vegetable which can be grown in most of Califor- nia. Approximately 15,000 acres are de- voted to sweet corn in this state, with a value of $6,000,000 in 1970 to the farmer. The per capita consumption of fresh sweet corn in the United States has been stable at about 8.0 pounds per person, and con- sumption of canned corn has been stable at about 5.5 pounds of processed weight per person. Use of frozen sweet corn has increased steadily, from about 0.65 pounds of processed corn per person in 1960 to 1.60 pounds in 1969. Almost the entire corn crop in Califor- nia is for home consumption. Most of it is sold fresh on California markets, but a small amount is delivered to freezers. A small amount is also shipped out of state, and a few out-of-state imports, primarily from Florida, are received in winter. Be- cause sweet corn is highly perishable, long-distance shipments are limited. In 1970 it was estimated that 25 per cent of the sweet corn crop in California was machine harvested. Where corn is grown Riverside, Kern, San Bernardino, Los An- geles, Alameda, Orange, Merced, and Contra Costa are the important sweet corn-producing counties. Smaller acre- ages are grown in other counties of the San Francisco Bay region, in most of the counties of the San Joaquin Valley, in the Delta region, and in San Diego County. In Riverside County most of the acreage centers in the Coachella Valley, with a small amount in the Palo Verde Valley. Chino is the main com district in San Bernardino County. The late spring marketing period be- gins in early May in the desert valley of Coachella and reaches its peak volume in June. These plantings are made in Janu- ary and February. During the late spring period, in the Kern district of the San Joaquin Valley harvest from plantings made in late February and March begins about the middle of June and reaches a good volume very rapidly. The second main marketing period is earhj summer, with harvest in July and August. Plantings for this period are made in late March through June in the San Francisco Bay area, Sacramento Valley, San Joaquin Valley, and southern Cali- fornia. The fall crop harvest from Kern, Los Angeles, Orange, Merced, and Riverside counties begins in October and ends by the middle of December. These plantings are made in July and August. Highest prices are received for the earliest and latest production. Lowest prices usually occur during July and Au- gust. The peak harvest period in Califor- nia is June through August. Production during May, September, October, and November is about one third that of the peak months. Favorable growing conditions High sweet corn yields depend on plants Seeding and harvest dates for sweet corn, District Usual planting period Main harvest period Coachella Valley San Joaquin Valley Southern California San Francisco Bay area Delta region January to March August March and April June and July March to July April to July April to June May and early June November and early December June to early August October to early December Late June to early November July to October Late July to September [3] having the best environment at every stage of growth. Warm days and nights provide the best climatic conditions. Frost will injure the plants at any stage of growth. For germination, soil tempera- tures between 70° and 80 °F are best, and should not be below 55°F. Air tem- peratures above 95 °F or hot, drying winds may cause poor pollination, and if such conditions prevail during harvesting, sweet corn will pass through prime con- dition very quickly. Also, diseases such as ear rot are likely to develop if the weather is very hot and humidity is high. Sweet corn is grown on all soil types, from sandy loams to clay loams, as well as peats or muck. Sandy loam soils are preferred for the early spring crops. Sweet corn appears to be moderately tolerant of salt and alkali. Growing periods differ in length . . . The length of the growing period from seeding to first harvest varies with variety, planting date, season of the year, and district. January plantings of Golden Cross Bantam types in the Coachella Valley may take 110 to 120 days to reach maturity, while late February seedings take 90 to 100 days. April and May plantings in the Central Valley take 75 to 100 days; in the coastal counties, 95 to 120 days. The growing period for most of the early or quick-growing varieties ranges from 70 to 110 days; they usually mature 5 to 15 days sooner than Golden Cross Bantam planted at the same time. Sum- mer plantings for fall harvest will require a longer growing season than midspring plantings. The hand harvest of one plant- ing usually extends from 4 to 10 days. When harvesting is by machine, the en- tire crop is removed at one time. Yield is variable Yields range from 150 to 325 crates per acre. Late varieties normally yield higher than early-maturing ones, and crops grown under favorable conditions produce more than those subjected to long pe- riods of cool weather, short days, or ex- cessively high temperatures. The ear weight of Golden Cross Bantam may vary from 5 to 8 pounds per dozen, depending on the growing conditions. What variety to plant A golden corn that produces large ears of good quality is preferred at the present time. Hybrid varieties give higher yields, Characteristics of several sweet corn varieties — 1969 tests (Kern County) Plant Ear Ear Number of Variety Days to height diameter length tillers SCMV Smog and source maturity (feet) (inches) (inches) per plant tolerance f tolerance! Bonanza (FM) 88 6.7 1.8 8.0 0-1 + + Valley Market (FM) 90 6.7 1.8 8.0 1.3 + + 58-1804C (R) 86 6.5 1.9 7.8 2.4 + + Buttersweet (K) 90 7.5 1.9 8.0 1.7 + + Earlibelle (H) 80 5.5 1.7 7.5 2.9 + + Merit (A) 90 7.5 2.0 7.8 2.3 + + Golden Cross Bantam "T" (C) 79 5.9 1.6 8.3 1.8 — - Jubilee (R) 88 7.0 1.8 8.0 1.0 - + NK 6962 (NK) 85 5.6 1.6 8.0 0.1 + + ° FM = Ferry-Morse; R = Rogers Bros.; K = Keystone; A = Asgrow; H = Joseph Harris Co.; C = Crookham; NK = Northrup, King. f Rated tolerant (+) or intolerant (-) based on severity of sugar cane mosaic symptoms and leaf edge scorching. } None to slight damage (+) and moderate damage (-). [4] are more uniform in maturity and type, and are of better quality than the rarely grown open-pollinated varieties. There are countless varieties of sweet corn avail- able, with great variation in plant size, ear size, time of maturity, and quality. The popular varieties for a particular area are constantly changing. Golden Cross Bantam "T" strain and AM, NK, and FM Cross strains are stan- dard hybrid varieties grown in the state, but these are susceptible to smog damage and sugar cane mosaic virus. Jubilee is a standard hybrid variety with excellent eating quality, but is sus- ceptible to the sugar cane mosaic virus and is difficult to machine harvest. Bonanza and Valley Market are two new hybrids showing exceptional promise in California as new varieties with toler- ance for the sugar cane virus and smog damage, as well as having good eating quality. In the future more emphasis must be placed on the adaptability of varieties to machine harvest. Seed production Very little sweet corn seed is produced in California. Hybrid seed is grown by com- mercial seed companies located mainly in the northwestern and middlewestern areas of the United States. Do not save seed from hybrid corn, because it will be variable in the next generation. GOOD CULTURAL PRACTICES WILL PAY OFF IN HIGHER YIELDS OF BETTER CORN Field preparation In the Coachella Valley it is customary to preirrigate to leach out excessive salts and to provide moisture for preplanting tillage and for germination. In this region early spring plantings are made on high peaked beds spaced 36 inches center to center. The corn is planted on the south side of beds running east and west, with the seed row about midway between the furrow and the peak of the ridge. The ridges are thrown up with lister shovels and shaped either before or at planting with special bed shapers. In other areas and for later plantings in the Coachella Valley, sweet corn is gen- erally planted on the flat. A pre-irrigation may be used to leach down soluble salts and supply moisture for germination of summer plantings, or the crop may be planted in dry beds and then irrigated. Preplanting tillage should be just enough to work in crop residues and prepare an adequate seedbed. Seed Use a good grade of seed. There is con- siderable variation in seedling vigor and time of maturity with different-size seeds, and for this reason growers should use seed which has been sized. It is essential that all of the crop mature at the same time, especially if it is to be harvested mechanically. When seed is planted in cool, wet soil, treatment with a fungicide may prove beneficial. Most seedsmen treat their seed with both a fungicide and an insecticide before it is offered for sale. Spacing Sweet corn is usually drilled in rows 36 inches apart, though this spacing may be adjusted to the equipment to be used. A desirable plant spacing in the row is 8 to 12 inches between plants of irrigated corn. If the stand is thicker than this, thin to these distances when the plants are 3 to 4 inches high. Plant the seed 1 to 1/2 inches deep, and firm the soil well over the seed. About 15 pounds of seed per acre are suggested for plantings in early spring, when germination may be poor. For later [5] k? V I 'I I * \ ** .. . Planting early sweet corn on the south side of the ridge promotes early growth by raising i soil and air temperatures around the seed and seedlings. It also affords some frost protection. plantings 10 to 12 pounds per acre are adequate unless kernels are quite large. Increasing plant populations to 16,000 and 20,000 per acre has shown a marked yield advantage in some areas. Special bed shapers with drills attached have been developed in the Coachella Valley for planting on the side of the ridges. With flat plantings or even for planting on high ridges, corn planters or small vegetable seed drills may be used. Make several successive plantings if you want a long harvest period. The in- terval can vary from 3 weeks between early spring plantings to 1 week or even less in late spring. Climate is the key factor for planting dates; whether successive plantings are made at intervals of a week or more, or early, medium, and late varieties are planted at the same time, the aim is for the highest efficiency at harvest. Sched- uling of plantings and harvesting becomes even more critical with machine har- vesting. Fertilizers Sweet corn requires much nitrogen throughout the growing period, and nitro- gen fertilization has proved profitable in all areas. About 200 pounds of nitrogen per acre are recommended for early spring plantings, particularly on lighter soils; 100 pounds of nitrogen per acre should be adequate for later plantings and for plant- ings on heavier soils. Nitrogen leaches [6 rapidly from the light sandy or sandy loam soils commonly used for the earliest production. To reduce leaching, am- moniacal forms of nitrogen such as am- monium sulfate, ammonium phosphate, aqua ammonia, and anhydrous ammonia are commonly used. Neither anyhydrous nor aqua ammonia should be injected closer to the plant than 6 inches, because of the danger of burning young seedlings. Phosphorus applications are usually beneficial on early plantings in the desert valleys and on many soils in Kern, Fresno, and Tulare counties. A rate of 40 pounds of phosphorus (100 pounds of PlOs) per acre should be adequate. All the phos- phorus and at least one third of the nitro- gen should be applied at planting time. With heavy applications it is satisfactory to broadcast the fertilizer and work it into the soil. Sidedress applications should be made 4 to 6 inches to the side of the row and about 4 inches deep in the soil. The remaining nitrogen should be applied by the time the crop reaches the tassel stage. From the stage of tassel initia- tion until the tassel emerges, the plant grows at a tremendous rate both in height and in the size and number of leaves. Re- quirements for nutrients, particularly nitrogen, and for moisture increase sharply at this stage. Shriveling of tip kernels on the ear often occurs in plants that are deficient in nitrogen as they ap- proach maturity. Experiments in the Coa- chella Valley showed that this trouble could be reduced by nitrogen applications at the early tassel stage. Most California soil contains enough of the other nutrients (potassium, mag- nesium, iron, and so on) and, therefore, these seldom need to be supplied in fer- tilizers. However, zinc deficiencies have been found in several production areas of the state. This deficiency affects both quality and yield. In areas known to be zinc deficient, from 10 to 20 pounds of actual zinc per acre should be worked into the top 8 to 14 inches of soil sur- face preplant. Barnyard manure may be used to sup- plement chemical fertilizers. Experiments in the Coachella Valley showed that manures were good sources of phosphorus and potassium, but could not be used to supply the entire nitrogen requirement. When used, barnyard manure at 10 tons per acre or poultry manure at 4 to 5 tons should be worked into the soil and the soil preirrigated before the crop is planted. This is necessary to leach soluble salt from the manure. Heavy applications of manure are likely to result in excessive salts in the soil. Weeding and cultivation One or more early cultivations are needed to control weeds and to establish irrigation furrows. Some weeding can be combined with thinning operations. Keep all culti- vation close to the plant shallow to avoid disturbing the root system. Chemical weed control is often used with sweet corn. Because recommendations vary from one district to another, and because new chemicals become available, obtain latest information from your local Uni- versity of California Farm and Home Ad- visor's Office. Irrigation Young sweet corn plants have a rather coarse, shallow root system, but as the plant approaches maturity, the root sys- tem becomes more fibrous and will pene- trate to a depth of 3 feet (or slightly more in tall varieties with a large plant). A crop requires 12 to 25 acre-inches of water. Summer plants in the interior valleys need more water than early spring plantings or crops grown on the coast. Irrigation in furrows is the usual prac- tice, though the flood method or sprin- klers can be used. With good soil moisture at planting time, an irrigation during the germination period is seldom necessary in cool weather. In hot weather, one irrigation during this period may be necessary to obtain maximum and rapid germination. Start regular irrigation when plants are 3 to 6 inches tall. This first irrigation can be quite important for obtaining maxi- mum yields; because of the relatively shallow root system, it may be needed even though the soil appears to be fairly moist. Intervals of 2 to 3 weeks between irrigations may suffice at first if the [7] weather is cool, but in warm weather and on light soils weekly irrigations may be necessary. Late fall plantings will require less frequent irrigations as the weather grows cooler. Apply 2 to 4 acre-inches of water at each irrigation. On hot days corn leaves may roll up for an hour or two without danger of injury, but irrigation is needed if leaves remain rolled up in the early morning. Leaves rolled as shown are a sign of insuf- ficient water. For best yields and ear size, do not allow corn to become this dry. Irrigation is often important when corn is about as high as shown in this photo. Later, water will be applied in every row to wet a maximum amount of soil. Adequate irriga- tion is essential for good production. •ML ,-" k -.";% K*** W j3* ^t fc> Suckering It has been said that suckering (removal of side shoots or suckers) will increase yield and size of ears, but numerous tests in California and other states have shown that removal of suckers is not beneficial. In these tests, neither yield nor size of ear was increased, and in some tests yield was materially reduced by suckering. A few tests have indicated that in early spring plantings the crop may reach the harvest stage a few days earlier if the corn has been suckered. Thus, this may be a factor to consider when first plant- ing in a district. But there has also been some indication that varieties may vary in their response to suckering, and so it is advisable to test the practice on your variety before deciding to sucker. Several of the new varieties being selected for machine harvest produce few or no side shoots. Some growers sucker their corn be- cause they believe it reduces the labor needed for harvesting and for treating corn earworm. This may be true, but it is unlikely that the savings will make up for the cost of suckering. A study at Davis showed that it took 13 hours of labor per acre to sucker, dust, and harvest 1 ton of corn. Less time was required for these operations in 1 acre of unsuckered corn. PESTS AND DISEASES MUST BE CONTROLLED Insect control Resistant hybrids and good soil-manage- ment practices help to reduce insect dam- age. Nevetheless, sweet corn in Califor- nia is subject to attack by several insect pests which can be controlled only by chemical methods. Corn earworm. The best known and most destructive insect on corn in Califor- nia is the corn earworm. Earworms may be abundant on any planting, though they are usually more serious late in the season. The night-flying moth responsible for the earworms is light brown or buff colored, with a wing spread of about 2 inches. It normally lays its eggs on corn silks, the tiny, dome-shaped eggs hatch in 2 to 10 days, and the young worms (larvae) work their way down the silk channel to the ear. Sometimes eggs are laid on the tassels and the worms migrate to the ears later. Larvae leave the ears by boring out the side or by crawling out the tip; they then go to the ground to pupate. The larvae stage lasts 12 to 13 days. The pupae pass through the winter 3 to 5 inches deep in the soil, and adults emerge in certain areas as early as late March. The pupae stage is, except for the over- wintering forms, approximately 12 days long. Thus, the total life cycle is 29 to 30 days. Infestations are present as late as the middle of November. [9] With the exception of the lesser corn- stalk borer, the earworm is the most dif- ficult pest to control on sweet corn. Control. Inasmuch as chemicals and suggested rates used on corn may change from year to year as new pesticides be- come available, consult the University of California Farm and Home Advisor's Of- fice in your area for up-to-date recom- mendations on pest control. The corn earworm can be a serious pest. Usually treatment in the tassel stage is not economical. Wait until the silks ap- pear. Individual ear treatment (hand dust) with a stencil brush is often necessary for moderate to heavy infestation when silks first appear. Five to seven applications are necessary at 2- to 3-day intervals, or until silks stop growing. Some growers market some of their sweet corn as fodder for livestock. Be sure you know the time limitation for the particular chemical used to treat the fodder. Ground power spraying is often used for light to moderate infestations. Four nozzles are arranged per row (2 on each side) to cover the ears. Usually 5 to 16 applications are necessary, applied at 1- to 3-day intervals. Thorough agitation of the liquid is necessary. Ground power dusting is also used for light to moderate infestations, but is gen- erally less effective than ground power spraying. Use 5 to 16 applications at 1- to 3-day intervals. Thorough coverage is es- sential. Dust treatment by airplane is ef- fective only on light population levels, and is seldom practiced in California. Most of the chemicals presently used for corn earworm control are harmful to bees and should not be applied when bees are present. Dust and spray treatments by ground power equipment should be made only in late afternoon or at night, when bees are not visiting the field. Corn aphids. Several species of aphids, primarily the apple grain aphid and the corn leaf aphid, become abundant enough on corn to make the foliage and ears sticky with honeydew. A black, sooty mold develops on the ears and makes them unsightly. Control is usually not necessary. Armyworms and cutworms. Several species of cutworms and armyworms dam- age corn. Cutworms hide in the soil dur- ing the day and cut off the plants or bore up inside the stalks at the ground level. Armyworms often have the habit of marching like an army from one field to another, and may attack the plant at any level. The black cutworm and variegated cutworm often cut off small plants. The beet army worm prefers small plants, often [ Cutworm and damage to young corn plant. doing considerable webbing of the foli- age. The fall armyworm, on the other hand, attacks all stages and all parts of the corn plant, even the ears. Spider mites. The Atlantic two-spotted spider mite and others sometimes cause severe damage to sweet corn. The plants become yellow and are covered with a fine silk webbing. Spider mites may affect yield, but usually merely discolor or dis- figure the ears. Control, while usually not necessary, can be achieved by certain recommended materials. Lesser cornstalk borer. This borer is an occasional pest of seedling plants. The active caterpillars bore into the roots and stems at the ground level. Fall and winter cleanup of trash and crop rotation assist in its control. Darkling ground beetles. Small dark- ling ground beetles occasionally attack and girdle young seedling corn plants. Flea beetles. These small, jumping beetles often attack seedling plants, and may attack larger plants. They gouge out 10] An ear of corn showing severe smut damage. areas in the leaves, causing the leaves to dry back to the stalk. Seed corn maggots and wireworms. These pests feed on the germinating seeds. Seed can be treated prior to planting with a fungicide-insecticide mixture. Disease control In spite of sound cultural practices, sweet corn crops in California are prey to cer- tain diseases. Most common are the fol- lowing: Sugar cane mosaic virus. The sugar cane mosaic virus (SCMV) has become a serious problem in some sweet-corn grow- ing areas of the state. On susceptible standard varieties such as Golden Cross Bantam T-Strain and FM Cross, the dis- ease causes an interveinal leaf mottle, which is usually followed by severe leaf edge scorching and stunting. Severe infec- tions can reduce yields and, when infected at a very young stage, the entire crop can be lost. Presently there are no chemical controls for this disease. Through recent variety studies, a number of new varieties with good market quality and satisfactory tolerance to sugar cane mosaic virus have been found. These include Bonanza, Val- ley Market, C 3596, 58-1804C, Butter- nut, Earlibelle, and NK 6962. Smut. Boil smut, the most common dis- ease of corn in California, causes large, fleshy, irregular swellings on the stems, ears, or tassels, and may occur at any stage of growth. The spores survive in the soil; hence, the problem can be at least reduced by a crop rotation program. Seed treatment, which will prevent pre-emergence seedling loss from other organisms, is not effective in controlling smut. If corn smut occurs, remove the diseased plants or parts and destroy them, preferably by burning. Ear mold, pink rot. Several fungi, par- ticularly Fusarium moniliforme, may de- velop on ears in the field, usually in worm-damaged ears. The ears become moldy and the kernels may split open and turn a pinkish color, which ruins the corn for market. This trouble usually de- velops only in heavily irrigated fields dur- ing periods of high temperatures. Root rot. This disease, caused by one of the water mold fungi (Pythium gramini- cola), is known only in southern Califor- nia primarily on early maturing varieties grown in late summer. The leaves of in- fected plants roll up and wilt. Young plants die rapidly, while older plants (2 to 3 months old) often remain partially wilted for several days before dying. Roots of affected plants are brown and appear water soaked. The rot may ex- tend into the subcrown internode, but seldom above the cross. No general con- trol measures have been developed for this disease. Smog damage Leaf scorching is a symptom of smog damage, which can be differentiated from the scorching associated with sugar cane mosaic virus. Smog damage begins as dull, interveinal, water-soaked areas which later become streaks of dead tissue. Tolerance to smog damage has been ob- served in some sweet corn varieties. [ii IN HARVESTING, QUALITY DEPENDS ON CAREFUL TIMING OF OPERATIONS Development of the ear Good pollination is essential for well- filled, fully developed ears. The silks keep growing until fertilized by the pollen car- ried to them from the tassels by wind and gravity; then they begin to dry and some- times turn brown. Hot weather, dry winds, or dry soil conditions may cause failures in pollination or set of kernels. In summer, corn reaches a prime eating condition about 3 weeks after tasseling; in early spring or late fall the interval may be 4 to 5 weeks. In the Coachella Valley . m Field of commercial sweet corn. [12] during hot weather, harvest may occur as early as 14 to 15 days after tasseling. Tasseling is 3 to 4 days earlier than silk- ing. Generally, sweet corn is suitable for harvest 14 to 19 days after silking. When and how to harvest As the ear approaches maturity, sugar changes to starch, the hull becomes tougher, and the kernels pass through stages called pre-milk, milk, early dough, and dough. At field temperatures of around 60 °F, an ear remains in prime condition for about 5 days; at 85 °F it passes through this stage in 1 to 2 days. As the field approaches maturity, a few ears should be examined occasionally to determine the time for the first picking. An ear at the proper stage is full size for the variety, its husk is tight, and the silks are somewhat dried. The kernels are fully developed (yellow for golden varieties) and if punctured the kernels show a milky liquid. Because husks should not be dis- turbed during harvesting, the picking crews should examine only external char- acteristics in selecting the ears that are ready. The ears are harvested by hand with a downward twisting motion. In small- scale operations, the pickers carry a sack or other container which they empty into a larger container or vehicle at the end of the row. On large plantings, pickers toss the ears directly into trailers which carry the corn from the field. As all ears do not reach maturity at the same time, a field may be picked two or three times in order to harvest corn at the best stage. Machine harvesting. In 1970, approxi- Maturity of corn: the ear on the left is immature; that in the center is just right; the one on the right is overmature. Uniformity of field maturity is desirable for harvesting. Hand harvesting sweet corn onto conveyor belt mately 25 per cent of the sweet corn grown in California for the fresh market was machine harvested. The reasons for this are that machine harvesting can re- duce harvesting costs and improve yield, and harvesting can be done at night to take advantage of cooler temperatures, thus getting better quality in the corn. Therefore, it is anticipated that machine harvesting will increase each year and that the industry will be largely mecha- nized within a few years. In order to have economically feasible machine harvesting for the fresh market, there must be minimum mechanical dam- age to the ears, and the crop must mature uniformly so that it can be harvested at one time. Cultural practices which pro- mote uniformity of emergence, growth, and maturity should be followed. Me- chanical harvesting is improved by using new medium-height corn varieties having a single ear per plant, no suckers, and high plant populations. It is estimated that about 125 acres are needed to justify the capital investment for a self-propelled, 2-row, fresh-market corn harvester. Additional acreage per machine and yield per acre reduce the cost of harvesting. Some machines will harvest 10 acres during an 8-hour day. (There are both 2-row and single-row harvesters.) The small grower may prefer the single-row harvester. Some harvesting machines turn out ears with shorter shanks and less green husks than are found in hand harvesting. The general belief in the produce in- dustry is that green husks on sweet corn preserve moisture in the ears and main- tain quality; but studies have shown that more denting (loss of moisture) of the kernels occurs after storage for a few days when long shanks and flags are left on the ears. Closely trimmed ears had less moisture loss. Production costs Latest production-cost studies for Califor- nia sweet corn (made in Riverside and Contra Costa counties) indicate that it costs approximately $2.40 to produce a crate of corn; this is based on a yield of 200 5-dozen crates per acre and includes preharvest and harvest costs. The cost per crate will vary, however, depending on the time of year produced and also on whether packing and marketing costs [14] Unloading sweet corn from machine hopper. [15 are included. Continually rising produc- tion costs will make it necessary to re- evaluate production costs yearly. Harvesting and quality Sweet corn loses sweetness and freshness of kernels rapidly after harvest, with the rate of loss increasing with temperature. For example, at 50 °F sweet corn loses its sugars about three times faster than it does at 32°F; at 68°F, six times faster; at 86°F, 12 times faster; and at 104°F, about 24 times faster. To maintain maxi- mum quality, sweet corn should be har- vested during the coolest period of the day — at night and in the morning. Many growers now begin harvesting about 1:00 a.m. and cease before noon each day. Corn harvested early in the morning will be 10° to 25° F cooler than that harvested later in the day. Sweet corn has a high respiration rate and, therefore, produces much heat, which can cause ears in bulk trailer loads to heat up considerably during delays between picking and precooling. The longer the delay, the greater the heating and quality loss. To prevent this loss, sweet corn should be moved quickly from harvest to packing sheds, where it should be rapidly sorted, packed, and cooled. This is especially true for corn harvested from about middav on. To maintain maximum quality: • Harvest corn at night and as early in the day as possible. • Haul corn quickly from field to packing shed. • Process corn through the packing shed rapidly. Do not let bulk trailers of sweet corn stand for prolonged periods (e.g., during the noon hour) while awaiting unloading at the shed. • Precool the corn as thoroughly as possible. A few shippers precool (hy- drocool) prior to sorting and pack- ing. Use cold rooms for storing corn between cooling and packing, and after packing when needed. Sorting Good corn should have green, fresh husks with streamers and well-filled, long ears relatively free from defects. Discard all ears showing side holes made by corn earworms, smut, mold, or serious tip dam- age from worms. Most growers discard ears that have less than 4 inches of good kernels, that are under- or overmature, or that have severely damaged husks. Some growers separate corn into two grades according to length of ear. Only high-quality corn should be packed for market, as poor quality discourages re- peat sales. Sweet corn offered for sale must meet the following minimum requirements of the California Agricultural Code: Ears of green corn shall be free from serious damage caused by smut or other diseases, mold, decay, or fer- mentation, insects, or other causes. Damage from any cause shall be con- sidered serious if it affects any of the kernels below a distance from the tip of more than 25 per cent of the length of the cob. In addition, the kernels on at least one half of the Shade should be provided for harvested sweet corn while waiting at packing shed. length of the cob shall be plump, milky, and well developed, but not shriveled. Not more than 10 per cent, by count, of the ears in any one lot of containers or bulk lot may be below these requirements, but no container shall have more than 20 per cent, by count, of ears which are below these requirements. As these requirements are subject to re- vision, be sure to consult the current Cali- fornia Agricultural Code or your County Agricultural Commissioner. Packaging Sorting and packing are hand operations normally performed in packing sheds, but which can be done in any shaded location on a ranch. When large quantities of corn are to be handled, well-organized pack- ing sheds are needed for efficient opera- tions. Packing sweet corn. Sweet corn is generally packed in wire- bound corn crates, with 4 to 6 dozen ears per crate, depending on the size of ears. The wire-bound crate has inside dimen- sions of 7% x 14 x 21% inches. In recent years a few shippers have packed corn in water-resistant fibre-board boxes (car- tons) holding the same number of ears as wire-bound crates. In crates and cartons corn is arranged in layers of 8 to 12 ears. Some corn is packed and shipped in vari- ous types of unlidded containers (apple boxes, L. A. lugs, and W.G.A. crates) to near-by markets. Precooling Sweet corn loses its quality (sugar) and appearance rapidly at high temperatures. Quick and thorough precooling followed by cold storage will help retain the quality. Precooling means fast removal of field heat. This lowering of the corn's tempera- ture also lowers its "rate of living" (respi- ration rate, etc.). Sweet corn should be precooled to as close to 32°F as possible, although it is rarely cooled below 40 °F in commercial practices. Methods of pre- cooling used are as follows: Hydrocooling. This is the most com- mon precooling method used for sweet corn; it consists of either showering the corn or immersing it in cold water. This transfers the corn's heat to the water, which is then conducted to an ice bunker or passed over coils of pipe containing a refrigerant (in mechanically refrigerated units); the cooled water is then returned to the shower or immersion tank for use again. When using ice-cooled systems it is important to remember that the ice must melt in order to cool the water. The water will cool faster with crushed ice than with chunk ice. A hydrocooler should be carefully de- signed to meet the needs of a shipper's operation. It should be large enough to cool an average maximum day's volume of corn without long delays between har- vesting and cooling. The cooler should be located in a shaded area, should have good insulation, and should have an ade- • Extracts from the Agricultural Code of California. Bureau of Fruit and Vegetable Standardization, Department of Agriculture, Sacramento. Revised to 1961, Section 813.7. [17] Hydrocooling sweet corn. Hydrocooling sweet corn in bulk bins. # wn quate but not excessive water capacity, because large amounts of water require more cooling (ice or refrigerant) to lower the temperature for effective cooling. Improper insulation and size of pump cause undesirable and costly heating of the water, thus reducing a cooler's effi- ciency. Hydrocoolers should be cleaned thoroughly after each day's use. A suit- able biocide should be added to the water to prevent build-ups of harmful fungi or bacteria. Vacuum cooling. Sweet corn can be precooled by vacuum cooling, although this practice is not common in California. In this operation, corn is submerged in cold water just before being placed in the vacuum tube, which increases surface cooling and prevents excessive loss of moisture from husk leaves during the vacuum cooling process. This method of precooling appears to be best adapted for custom vacuum cooling operations, be- cause of the high cost of facilities and operations. Package icing This is an excellent method of cooling sweet corn. It is used to only a limited extent in California, mostly for local, di- rect shipments, but its use for long-dis- tance shipments is increasing. Sometimes package icing is used after hydrocooling; growers who want to improve their corn's market quality should give this strong consideration. In this method, 15 to 25 pounds of crushed ice are distributed throughout the container during the packing process. The corn is cooled rapidly and efficiently because of its continued direct contact with the ice. If enough ice is used, some will remain in the container during the entire marketing period, thus greatly ex- tending the length of time low tempera- tures can be maintained. Water from melting ice helps to keep husks and streamers fresh. The amount of ice needed in a package depends on the tem- perature of the corn at the time of pack- ing and on the expected length of the Top-icing a truck load of sweet corn for shipment. [19] marketing period. Wire-bound corn crates and water-resistant cartons are used for shipping package-iced corn. The main disadvantages of package icing are that the pack may be somewhat slack on arrival in the market and the package is heavy and wet. Cold storage To maintain best quality, place sweet corn in cold storage immediately after precooling; storage can be in a refriger- ated truck or rail car, or in a cold storage room. Hold temperatures as close to 32 °F as possible without freezing the corn. The relative humidity of the air in cold rooms must be kept at 95 per cent or higher to keep corn fresh and to prevent drying of husks. Do not hold corn for more than a few days in cold rooms while accumulating loads, as quality loss in- creases with length of storage. Icing in transit The best method consists of blowing finely crushed ice (snow) over the top (top icing) and through the load (body icing) during loading of trucks and rail cars. The amount of ice used depends upon the temperature of the corn at loading and the distance to markets. This method of icing helps to keep temperatures low during transit, but provides little or no additional cooling. Icing in transit is de- sirable for hauls of 75 miles or more, es- pecially if the corn has been precooled or package iced. Unloads of California sweet corn in major U. S. markets — 1969 Region Month Tntnl and market May June July Aug. Sept. Oct. Nov. Dec. Carlots* Denver _ 1 2 _ _ 2 1 2 8 Los Angeles 66 155 392 242 149 88 58 45 1,195 Portland 15 27 15 1 - — 1 2 61 Salt Lake 3 16 3 — 1 — 1 — 24 San Francisco 34 101 175 107 48 16 21 9 511 Seattle 12 33 12 1 1 2 5 3 69 Vancouver 3 9 3 - - - 1 1 17 Total 133 342 602 351 199 108 88 62 1,885 * Carlot = 725 wire-bound crates. Source: USD A, Consumer and Marketing Service, Fruit and Vegetable Division. MARKETING . . . THE LOCAL MARKET IS USUALLY THE MOST PRACTICAL OUTLET Sweet corn is best adapted for marketing close to where it grows. Distant shipments are hazardous and should not be at- tempted unless the corn is of excellent quality and fairly free from worms, and unless its temperature can be lowered quickly to 38 °F or less and held there. If losses are to be avoided, sweet corn must be marketed in an orderly fashion even for near-by markets. Because it is highly perishable, it must be moved quickly. If the market becomes flooded, either prices drop drastically or much corn goes to waste. In recent years much sweet corn has been marketed directly through chain store outlets (arrangements for which are made prior to the marketing season). Corn is loaded at packing sheds directly into the chain store trucks and hauled to their distribution centers. This shortens the time from harvesting through retail- ing and helps retailers to offer higher quality corn to consumers. 20 by: Orderly marketing can be encouraged Timing the plantings to give a steady supply of corn during the entire har- vest period. • Offering only high-quality corn. • Maintaining uniform packaging and grades. • Advising marketing outlets in ad- vance when the harvest season will start and what changes are expected, so they can develop outlets before shipments arrive. • Avoiding heavy shipments when the market is filled with corn. Los Angeles wholesale market prices for sweet corn — 1969 Month California corn 1st and 3rd week Southern Central Florida corn Price per wire-bound crate (5 dozen ears) January 1st week 6.00-6.25 3rd week -7.00 February 1st week 5.75-6.25 3rd week 5.25-5.50 March 1st week 4.75-5.00 3rd week 4.75-5.50 April 1st week 4.25-4.50 3rd week 3.75-4.00 May 1st week -4.00 3rd week -4.00 4.00-4.25 June 1st week 4.00-4.25 4.00-4.15 3rd week -4.75 -4.50 3.75-4.00 July 1st week -2.75 2.75-3.00 3rd week 1.50-2.00 1.50-2.00 August 1st week 2.00-2.25 1.50-2.00 3rd week 3.25-3.50 September 1st week 2.25-2.75 3rd week 2.50-3.00 October 1st week 3.00-3.50 3rd week 3.75-4.00 -3.50 November 1st week 3rd week December 1st week 3rd week 4.25-4.50 -4.50 Source: Federal-State Market News Service, USDA, California Department of Agriculture. [21] Acknowledgments The authors wish to acknowledge the assistance of William L. Lange, Department of Entomology, Davis, Dennis H. Hall, Extension Specialist, Department of Plant Pa- thology, Davis, and Hunter Johnson, Jr. Agriculturist, Extension Service, Riverside. Co-operative Extension work in Agriculture and Home tconomics. College of Agriculture, University of California, and United States Department of Agriculture co-operating. Distributed in furtherance of the Acts of Congress of May 8, and June 30, 1914. George B. Alcorn, Director, California Agricultural Extension Service. 15m-6,'71(P4047L)VL r 22