AFTER 26 years or so of research, the first commercial hybrid corn seed for sale to farmers in any quantity was produced in Iowa in 1926.

Hybrid corn was planted on about 1 percent of the corn acreage in the Corn Belt in 1933 and on almost 100 percent in 1955. The wide adoption of high-yielding hybrid strains in 1938-1945 led to an increase of 15 to 20 percent in the average yield of corn in the United States.

The development of hybrids of grain sorghum followed discoveries of male-sterile characteristics in 1935 and later. Farmers accepted grain sorghum hybrids more quickly than they did corn hybrids. The first commercial seed field was planted in 1955. Nearly 70 percent of the acreage in 1960 was planted to sorghum hybrids.

The use of hybrid seed requires the production of new seed each year; the use of seed from farmers' fields of a hybrid would result in a loss of 15 to 20 percent in yield in the succeeding crop because of the reduction of hybrid vigor from inbreeding. An extensive business has been developed to supply the need.

Farmers need 10 million to 12 million bushels of seed corn and 1.5 million to 2 million bushels of sorghum seed each year. Large amounts of capital, labor, and technical knowledge are required of the specialized seed producers, which may be small farm-type operations or corporations. Some of the corporations conduct research on methods, develop inbred lines, produce and test hybrids, produce seed in their own plants, and sell directly to farmers. Much of the hybrid corn seed is produced by such firms.

CULTURAL practices for growing seed of corn and sorghum are similar in many respects.

Fields for seed are in high-yield areas that have fertile soil and favorable conditions of temperature and moisture.

Some corn seed is produced in irrigated areas, but much is produced in parts of the Corn Belt where normal rainfall is adequate.

Small amounts of grain sorghum seed are produced in humid areas, but more is produced west of the Corn Belt in irrigated areas where grain sorghum is a regular crop.

Before we had hybrids, seed usually was grown in areas where the variety was adapted. Seed fields for producing hybrid seed may be grown elsewhere, however, and the seed will be as well adapted as if grown locally. This is possible because hybrids are crosses of specific and uniform inbred lines, which change little or not at all when they are grown in different geographic areas or a different climate.

Potential yield in seed fields, weather risks (such as drought, high temperatures, hot winds, and hail), length of season, maturity of the hybrid parents, date of freezing temperatures, isolation from undesirable varieties, freight costs to the planned market, and other economic factors influence the decisions as to where to locate seed fields.

Seed of hybrids for the South, however, is grown in the South, and seed for the North usually is grown in the Corn Belt. Seed of corn hybrids for farthest northern areas often is grown 200 to 400 miles south of the area where it is best adapted to reduce risk of a freeze before harvest and to increase the size of the seed.

Regional limitations from south to north are not so great for most grain sorghum hybrids as for corn. Seed intended for Nebraska thus can be grown in Texas, or much of the seed for Texas can be grown in Nebraska.

Much of the seed is produced by farmers under contract with seed companies. The seedsmen pay certain costs, such as for the parent seedstock furnished to the growers and for the detasseling operation. High yields are thus mutually advantageous, and improved practices are applied to a greater degree than on the average farm. Some seed companies employ specialists who advise the growers on cultural practices.

It is important to get a stand of the correct number of plants to the acre. Heavy stands affect the size of the seeds and also the yield if drought and heat ensue.

An adequate supply of each fertilizer element is important for uniformity throughout the field, high-quality grain, early maturity, and the most profitable yields. Growers test the soil carefully before they apply fertilizers.

The use of herbicides varies with community and need. The use of 2,4-D to control broadleaf annual weeds in corn is common. The pre-emergence application of several newer chemicals controls both broadleaf and grassy annual weeds.

Weedkillers must be used with caution on grain sorghum for seed because the small, shallow-planted seedlings are susceptible to injury.

Many growers treat soil with insecticides—as spray or granules by broadcast or row application—against wireworms, rootworms, white grubs, seed corn maggot, seed corn beetle, cutworms, and others. Spray or granule applications to the growing plants are used to control the corn borer, corn earworm, corn leaf aphid, army-worm, sorghum webworm, grasshopper, and chinch bug.

Control of weeds in corn is important for maximum yields but is not important in obtaining weed-free seed.

Weed control in grain sorghum is essential in order to produce seed that is practically free of weed seeds and entirely free of seeds of noxious weeds. Sometimes a grower has to resort to hand operations to control weeds.

SEED FIELDS for corn usually are 40 rods from other corn of the same type and color. This distance sometimes is reduced when extra male rows are planted for added pollen production along the side of the field next to one on which corn is being grown for feed.

Fields of different types of corn (like white and yellow or sweet corn and field corn) must be at least 80 rods apart. Seed fields of waxy or other special endosperm types and special plant types, such as dwarf corn, have to be at least 40 to 80 rods apart to avoid contamination.

All volunteer plants within the field and in fence rows or lots within the isolation distance must be removed before the seed parent flowers.

Early planting is preferred in order to gain early maturity in the fall and to have the corn at safe moisture levels in the event of an early freeze. Germination of grain with moisture levels of 35 to 40 percent may be reduced in a few hours by temperatures of 26° to 28° F. Germination of the grain at a moisture content of 30 percent and less may escape injury.

Early planting in the Corn Belt increases the need to use chemicals to control corn borers.

Differences in maturity may require different planting dates for the seed parents and the pollen parents so that the silk emerges at the same time the pollen is shed. Because the difference in planting dates may be 2 or 3 weeks, problems in tillage may arise. Control of weeds by chemicals may be especially helpful in such instances.

Heat units are often used as an aid in estimating when to plant the delayed seed parent. A heat unit is the number of degrees the average daily temperature exceeds a base—usually 50° F. for corn—near the low temperature at which growth occurs. Thus, with an average temperature for the day of 62°, 12 heat units occur.

Records from special nursery plantings give comparable data as to the heat units to flowering and silking for the different seed parents when they are planted at the same time. Such records tell whether the two parents will nick at flowering time or, if not, how much the early parent must be delayed in date of planting. With a difference of 100 heat units, it is necessary to delay planting the early parent until 100 heat units have occurred.

The system is not infallible. In seasons when May temperatures are well above normal, the delay may require 10 to 20 percent more heat units than normal. Similarly, in cool seasons, the number of heat units required will be fewer than normal.

Seed fields usually are planted in alternating strips of two rows of the pollen parent and six rows of the seed parent. Extra pollen rows are planted on the sides of fields or across the ends, as may be needed for mechanical convenience (to make it easier to use machinery on odd-shaped fields, for example) or for border rows as protection against nearby corn.

DETASSELING of corn is the removal of the tassel from each plant of the female seed parent at the proper stage of growth but before pollen is produced. The tassel on an individual plant may be pulled during a period of 6 to 18 hours. Because plants differ in time of tasseling, however, the time in which a field is detasseled may be from 5 to 10 days.

Crews must patrol each row four to seven times during the season and must go over the fields every 24 to 48 hours. The workers walk or ride through the field. They remove the tassel by a gentle upward pull and drop it to the ground. This procedure does not reduce the grain yield very much.

Detasseling crews often include girls, women, and boys who are available for part-time summer work. Adults are sometimes hired on a contract arrangement that allows them to de-tassel on a piecework basis. They get higher hourly wages than the younger workers.

Standards for detasseling vary somewhat by producer and by State certification agencies. In general, detasseling must be done so that not more than 1 percent of the tassels are shedding pollen in any one day. The total cumulative shedding for any three inspections must not exceed 2 percent. These tolerances are met without difficulty, except in bad weather.

Heat units are used in estimating the acreage that may require detasseling on any given date. The projection of date of flowering, using heat-unit data, thus gives the detasseling date for each field and an acreage total by date, even though fields were planted at different times and the hybrids vary in heat units they require for flowering. Such estimates are approximate. The heat-unit differences among varieties are sufficiently consistent so that the projection of acreage by varieties from the planting date base will give good estimates of acreage to detassel on succeeding dates during the season. The number of heat units required differs between seasons, but adjustments for this variation from normal can be made at intervals before the detasseling season so that the accuracy of estimates increases with the season.

THE USE of male-sterile seed parents avoids some detasseling of corn.

Plant breeders have developed special strains of inbred lines in corn and sorghum in which the male flower does not develop normally and does not produce pollen. With a double cross, as is common in corn, the female (or ear seed parent) also can be male sterile. Thus a male-sterile female seed parent grown in alternating rows with a normal male-fertile line of corn as a source of pollen will cross naturally and produce hybrid seed on the rows of male-sterile type.

Some strains of corn do not produce pollen because of inhibiting factors in the cytoplasm—the protoplasm, exclusive of the nucleus. The cytoplasmic-sterile factor is bred into the seed-parent inbred line of the seed-parent single cross. This single cross cannot produce pollen. When the sterility-inducing cytoplasm is introduced into some lines, it is necessary also to breed out genes that can counteract the sterility. The breeding and testing techniques for making seed by the cytoplasmic-sterile method are complex.

Cytoplasmic-sterile female corn that is crossed with the normal male produces double-cross hybrids that are essentially the same as those produced by detasseling methods, except there may be sterility in the double-cross plants in the farmers' fields.

The cytoplasmic-sterile method involves planting part of the seed-parent acreage to the normal parent, which requires detasseling, and part to the cytoplasmic-sterile parent, which does not require detasseling, and then effecting a satisfactory blend of the seed from two female types.

The blend may be made by growing the corn in separate fields, sizing—screen separations according to width, thickness, and length of kernel—the lots separately, and making a known blend of the different sizes. This method usually is more expensive, and it requires additional facilities. More commonly, the seed field is planted in alternating strips of about 12 rows of the regular seed parent and 12 rows of the cytoplasmic-sterile seed parent when the field blend is to be made on a half-and-half basis.

A modification of the male-sterile method may make unnecessary the blending with nonsterile seed and thus eliminate detasseling in the production of certain corn hybrids.

This method involves the planting of all rows of seed parent to the cytoplasmic-sterile type and the use of restorer lines in the male. The restorer line restores fertility and causes the seed sold to farmers to produce pollen. The method has considerable promise, but more investigation is needed to produce good lines that also have appropriate cytoplasmic-sterile and restorer characteristics.

Ear corn from seed fields is harvested and dried on the ear to 12-percent moisture before shelling. Harvest begins at 30- to 35-percent moisture in the grain, when the plant has attained physiological maturity and maximum production of dry matter in the grain.

Harvest may begin at 40-percent moisture in cool, slow seasons to reduce the chances that part of the crop may be damaged in germination from severe early freezes. Four to 8 hours of exposure to temperatures of 25° to 28° may reduce germination of seed containing more than 30 percent of moisture. Slow maturity in the fall usually occurs in years with abnormally low temperatures in June.

Small amounts of seed corn are harvested with combines or picker-shellers at a 12-percent moisture level in some places like the Central Valley in California and parts of the South.

Drying facilities for ear corn make early harvest possible and enhance the quality of the seed by avoiding damage from freezing, reducing insect damage, and arresting the development of ear rot organisms. Early harvest avoids picker losses of 5 to 7 bushels an acre, compared to harvest at low moistures safe for cribbing.

The seed fields are harvested with mounted two-row cornpickers modified by removing the pegs from snapper and husker rolls, releasing the pressure on ear-retarding units at the husker rolls, and driving squarely on the row at slow speed. With these precautions, corn of high moisture can be harvested without serious damage to the kernels at the butt end of the ears.

Special facilities for handling seed corn have been built throughout the Corn Belt. The crop is received from the seed fields at harvest. Drying, sizing, cleaning, and preparation for delivery to the customer follow. The facilities may cost 200 thousand dollars.

A small plant may have a drying building of four or more bins that hold 5 thousand bushels of ear corn at one fill. Its air blowers and furnace are big enough to dry this quantity. Plants that have drying capacities of 15 thousand to 30 thousand bushels are common.

The plants are equipped with conveyors, elevators, storage bins, warehouses, cleaning machines, and handling facilities so as to provide a continuous operation. As harvest progresses, the drying bins are filled five to seven times in one season.

The operations before drying are picking, trucking, and unloading; taking samples; and running the corn over huskers to remove husks, silks, and trash and over sorting belts to remove offtype and moldy ears. High-moisture ears may be removed, especially if there has been a freeze of 28°.

Corn must be harvested from the field no faster than it can be dried at the plant. Intermediate storage is not possible, because the germination of ear corn of high moisture may be reduced by heating if it is held in bulk without ventilation. There is no damage if drying starts within 24 hours after picking in the field.

Shelling, sizing, and cleaning are done with equipment supplied by manufacturers who service the industry. Shellers, elevators, and conveyors are operated at slow speeds to reduce damage from mechanical handling. Bins are shallow. Devices are used to reduce abrasion as the grain is dropped into bins. Such care is necessary because seeds damaged mechanically may give a weak germination if extremely wet, cold soil conditions prevail in the spring.

Modern plants provide good storage facilities. Seed stored in bulk bins are aerated properly to prevent migration of moisture and the development of mold during storage.

Large warehouses are required once the finished seed is put in bags. Some warehouses are air cooled for summer storage so that the maximum temperature is 50° and relative humidity is 55 percent.

Because tonnages are large, mechanical handling methods are used. Sonic plants use fork trucks for transporting boxes of bulk grain and transporting and warehousing bagged seed on pallets.

Equipment for sizing and cleaning requires an investment about equal to that required for drying facilities. Sizing and cleaning usually begin as soon as shelled corn is available after drying and is completed in February, so that the seed can be distributed for spring planting.

The kernels are sized according to width and thickness to give uniform sizes that will fit the cells of planter plates. Special machines are used to remove the short kernels—length sizing—so that the seed will be more attractive and planting will be more accurate. Grade is often taken to mean the same as size, but there is little difference in productivity of seeds of different sizes.

Gravity cleaners, which separate corn according to weight, use a combination of vibration and air flotation to remove cracked, moldy kernels and light kernels. Special aspirators are used if air cleaning is sufficient.

Fungicides are added to protect the seed against various micro-organisms in the soil, which may cause seed rot during cold, wet weather. Fungicides in use for corn and grain sorghum are almost exclusively organic fungicides. Thiram or captan is their active ingredient.

Producers seldom add insecticides to corn seed. A few apply dieldrin to the seed to give protection against insects like the seed-corn maggot and grape colaspis and partial protection against wireworms.

A commoner practice is for the farmer to add an insecticide to the seed at planting time. Some insecticides must be added only at planting time because seed is damaged by prolonged contact with them or because they lose their effectiveness after several months. Methoxychlor or malathion is added sometimes to the fungicide to give protection against insects in storage.

A cold-test germination technique has been developed as a measure of quality in corn seed. The seed is placed in soil for 6 to 8 days at temperatures of about 50°. The samples then are transferred to warm chambers for germination. The test approximates damage to seed during cold, wet field conditions. As it is a biological test and conditions cannot be fully standardized, it is not suitable as a legal requirement. There is a high correlation between field stands under cold, wet conditions and such tests.

GRAIN SORGHUM seed fields require isolation from other sorghum. Isolation needs to be a minimum of 40 rods from other types of grain sorghum and 60 rods or more (usually 1 mile) from forage sorghums, hegari, sudangrass, and broomcorn.

Extra pollen rows often are planted along the sides of the field, but the separation from other fields is not reduced. Volunteer plants or outcrosses of forage types must be removed if they occur in nearby fields of grain sorghum, since distance requirements for forage types are more than for the grain types.

Because dwarf types of grain sorghum carry recessive genes for height, effective isolation is necessary to give seeds free of tall outcrosses. Broomcorn, sudangrass, sorghum almum, forage sorghums, silage sorghums, and certain grain sorghum varieties, as hegari, therefore are serious sources of contamination, and seed fields should be separated as far as possible from them. Outcrosses to some of these crops also have unwanted brown seeds.

Johnsongrass will cross with grain sorghum occasionally. Such outcrosses are particularly conspicuous and objectionable. Special isolation is essential where johnsongrass occurs. An isolation distance of one-half mile or more is desirable.

Seed of grain sorghum must be produced on land where sorghum did not grow the preceding year—some growers prefer 2 years to assure against volunteer offtype plants in the field.

A sorghum occurring as weed patches in many fields, especially in parts of Kansas, is identified variously as "chicken corn" or wild sorghum or Sorghum drummondii. It is taller than grain sorghum and has black heads because of the dark color of the glume. Seed must not be grown on or near badly infested fields.

Weeds must be controlled in seed fields so that weed seed will not be harvested with the grain. Seed cleaning, however, removes most weed seeds except those of johnsongrass, bindweed, morning-glory, and some others.

Standards of purity provide that no seeds of noxious weeds and not more than 0.05 percent of common weeds be present.

The production of hybrid seed of grain sorghum utilizes a cytoplasmic male-sterile female or seed parent and a restorer line as the male or pollen parent. Thus none of the heads in the female rows should produce pollen.

The rows require patrolling to remove any plants with heads showing fertility. Grain sorghum flowers are complete, and normally about 90 percent are self-fertilized.

Because detasseling, as with corn, is not possible in grain sorghum, a male-sterile method is required to produce hybrids of grain sorghum.

A genetic-sterile method was used to produce the first commercial seed of the hybrids distributed in 1956, but it was discontinued.

Hybrids of grain sorghum are of such recent origin that many seed-production practices still are not proved. Practices that were considered all right in 1961 very likely will be improved with increasing specialization in the production of more expensive seed. Longer experience may reveal that particular sections and techniques produce seed of better quality.

Locality is important. Northern areas, such as Nebraska, South Dakota, and Iowa and parts of Missouri and Kansas where johnsongrass is not common, have little difficulty in producing seed free from outcrosses to johnsongrass or sorghum almum types. Where the growing season is short, as in Nebraska, Iowa, and South Dakota, however, the seed must be early in maturity and harvested early in the fall to avoid frost damage.

Irrigated land is the most suitable for seed production, because ample soil moisture insures uninterrupted growth, maximum yields, and a minimum of pollen production in the male-sterile parent. Furthermore, harvest may be hastened, and fields may mature more uniformly because irrigation can be stopped at the proper time.

Weathering and discoloration of sorghum seed and sprouting in the head are hazards, especially in the more humid areas. Germination in the head may occur during damp autumn weather. Production in regions of high risk of frost damage may require a harvest method in which the heads are removed from the plants and dried in large driers, much as the ears of corn are removed from the plants and dried.

Production of sorghum seed in the Southwest has advantages: A long, frost-free season; low humidity at harvesttime; high yields and large seeds; harvesting with combines; the need to dry only in certain seasons; nearness to the market; and low seed costs.

The greatest hazard in southern localities is outcrossing with johnsongrass, sorghum almum, or forage types. Care in selecting isolated fields in places with a minimum of offtype sorghums can insure pure seed.

Seed set is more difficult in sorghum seed than in corn. The sorghum plant is sensitive to changes in heat, moisture, and length of day.

Kafirs react differently from milos. Seed fields with good seed set usually give seed that is low in outcrosses.

The planting of 4 rows of the pollen parent alternating with 12 rows of the seed parent is most convenient mechanically, although the 2-and-6 combination is followed in southwestern Iowa.

With the 4-and-12 combination, a 4-row planter can be used where the parents are planted on different dates. A self-propelled combine can gather readily the four rows of the pollen parent before the seed crop is harvested.

The proper timing of planting parents with different flowering dates sometimes is difficult. Low frequency of outcrosses is expected when the parents nick at flowering and a large part of the female florets are pollinated in a few days.

Hybrids requiring different planting dates for the parents need increased isolation and careful attention at planting time. Extra pollen rows around the field may improve seed set, especially at the ends and on the side of prevailing winds.

When seed set is low and temperature and humidity are favorable, the female florets may remain fertile for a long period after the male-row pollen has been shed. The risk of outcrossing then is high. This risk is greatest with adequate rain and mild temperatures.

We need some method whereby we can end the period during which the stigmas in the female florets are receptive to pollen.

In roguing seed fields of grain sorghum to remove offtype or undesirable plants, it is necessary to pull up the entire plant instead of merely removing the heads, because late tillers and side branches may flower and produce seed. In irrigated fields or in humid areas, precautionary measures are necessary to prevent uprooted plants from again taking root in the moist soil.

Both pollen rows and seed rows are rogued carefully. The male requires special care to reduce the amounts of undesirable pollen in the field. In female rows, fertile and offtype plants must be removed before they shed pollen.

Offtype plants may differ from the majority in such traits as height, head type, color of anthers and plants, and presence or absence of awns.

Most dwarf types tend to produce mutants toward tallness in ratios of about 1 to 1,000 plants. They are removed as offtype. Plant breeders have started work to develop types without tall mutants.

Plants that show evidence of pollen fertility in the cytoplasmic-sterile parent are removed as the anthers emerge. Some pollen is shed, because the anthers must emerge before the plants can be identified. Frequent patrolling of the rows during pollinating time therefore is necessary to reduce self-pollination, which would produce non-hybrid seed, which yields less than hybrid seed and sometimes gives off-type plants in the farmers' fields.

Certification standards for tolerances on fieldwork vary. An example: The maximum tolerance is not more than 1 definitely offtype plant per 2 acres; not more than 10 doubtful offtype plants per acre; no head smut; not more than 1 head in 100 with kernel smut; and no uncontrolled areas of field bindweed, hoarycress, Russianknapweed, or johnsongrass. If field inspection shows evidence of hedge bindweed, morning-glory, or velvetleaf, special measures must be taken in connection with inspection of the grain.

Most producers of hybrid seed have followed a practice of making special harvests from their seed fields during October to get representative samples of seed for planting in winter observation plots in Mexico, Florida, Jamaica, or southern Texas. Such winter plantings usually mature sufficiently to determine purity before the seed is to be sold. The seedsman thus can withhold undesirable lots.

MOST SEED of grain sorghum is combined at moisture levels of 13 percent and less. Drying therefore is not needed. Aeration may be needed in some areas if such combined seed is stored in bulk.

Some seed is harvested at 16- to 18- percent moisture and then dried to a maximum moisture content of 12 percent in batch or continuous-flow driers.

An important consideration in determining the maximum air temperature for drying seed is the time required for drying, because it determines the length of time the seed remains in contact with heated air.

A maximum air temperature of 95° is recommended for drying deep depths (3 to 6 feet) of seed of 16- to 18-percent moisture. In tests in Texas, an air temperature of 120°, with the seed exposed to the heated air for 2.5 hours, was not injurious to the germination of seed dried in thin columns to inches thick. A maximum air temperature of 110° is normally recommended.

Even though seed is cooled as a part of the heated-air drying operation, the temperature of the seed is usually above normal when it is placed in storage. It should be stored in bags therefore, or some provision should be made to cool seed after it is stored in bulk. A practical and economical method of doing this is with an aeration system that uses a motor-driven fan to move small amounts, one-tenth to 1 cubic foot of air per bushel a minute, of air through the stored seed.

Another procedure is to harvest heads at moisture levels of 25 percent in the grain, dry with air at a temperature of 110°, and thresh with a reduced number of concaves in the thresher.

Sizing and cleaning seed of grain sorghum requires less equipment than for corn, because the small seed does not require sizing. The necessary operations include scalping, to remove large grains; screening out the extremely small grains; and screening and air cleaning to remove weed seeds. The clean product is given fungicide protection (with thiram or captan) and then weighed and packaged in 50-pound bags, ready for delivery.