Key management practices for organic corn production include the following:

• Choose organically grown (when possible), non-GMO hybrids with high vigor, high standability rates, disease and pest resistance, stress tolerance, high yield, and a maturity date of 112 days or less.
• Plant on time, at the proper depth, in a well-prepared seedbed, on narrow rows.
• Rotate crops.
• Achieve proper soil pH and good fertility.
• Choose the correct plant population.

For organic growers seeking to identify appropriate corn hybrids, while yield should be considered, it is not the primary consideration. The key hybrid characteristics for organic corn production are as follows:

• Rapid early growth and vigor
• Standability
• Pest and disease resistance
• Stress tolerance
• Yield

Rapid Early Growth and Vigor

Rapid early growth is essential in minimizing the effects of seedling diseases and insects, increasing root volume, and in reducing weed infestation. Hybrid seed companies list seed vigor ratings. However, there are few that have ratings covering early growth. In general, early growth is closely related to hybrid maturity. Early-to-medium-maturing hybrids (102- to-114-day relative maturity) tend to exhibit better early growth than do late hybrids (>115-day relative maturity). The best way to select hybrids with rapid early growth for North Carolina is to contact extension agents, seed company representatives, and other growers who have had experience with different corn hybrids.

Standability

Standability is important because it is a measure of how well the crop will stand under difficult environmental conditions. Since pests and diseases can be problematic, it is important that an organic hybrid has the ability to avoid lodging under stress. Most hybrid seed suppliers provide ratings for standability or stalk or root strength.

Pest and Disease Resistance

Resistance to common seedling, leaf, and stalk diseases is an important characteristic for hybrids in organic production systems. There are even some hybrids that tolerate insect pests such as European corn borer and southern cornstalk borer. The extensive adoption of Bacillus thuringiensis (Bt) corn by conventional growers has lowered populations of European corn borer and southern cornstalk borer and brought about positive results for organic corn farmers. In conventional systems, corn efficiently manages borers and has decreased their populations significantly overall, leading to minimal issues from borers for most organic corn growers. Unfortunately, most hybrids do not have resistance to a wide range of diseases or pests. Growers should select hybrids that combine good early growth characteristics with a good resistance package to diseases that are major problems in their area. In North Carolina, the major diseases of corn are gray leaf spot, Northern corn leaf blight, and Southern leaf blight.

Yield

Unfortunately, variety testing of corn under organic conditions is sparse. Past North Carolina trials can be found on the NC State Extension Organic Commodities website. Given the rapid turnover of hybrids, test results can rapidly become outdated. Growers should conduct their own hybrid comparisons by selecting four to six promising hybrids and evaluating them on their farm with their management practices. The best procedure for grower testing of hybrids is the strip test where each hybrid tested is grown adjacent to a common "tester" hybrid. The strip test, with tester hybrids, permits any yield data collected to be adjusted for soil variability. If not using a tester, growers should place the hybrids they are considering beside the hybrid that has performed best for them in the past. Growers conducting their own hybrid evaluations must remember to select uniform test fields with minimal soil variability and restrict comparisons to hybrids of the same maturity.

Planting date is a crucial factor in the success of an organic production system. Planting too early results in slow growth and increases the amount of weed competition, the incidence of seedling diseases, and the likelihood of damage from seedling insects. On the other hand, planting too late results in a greater risk of drought stress, increased insect damage from second and third generations of European corn borers, and reduced yield from a decrease in intercepted sunlight due to decreasing hours of daylight. The recommendations here attempt to balance these considerations. In the tidewater and coastal plain, plant organic corn between April 15 and May 15. In the piedmont, plant organic corn between April 20 and May 20. In all locations, plant corn following at least two days when average temperatures are above 65ºF. Depending on the soil type, timing soil preparation and planting date to ensure soils are moderately dry at planting can minimize the risk of seedling diseases.

Seedbed preparation should begin with a major tillage operation performed at least a month before planting. If cover crops are used, they may need to be killed or incorporated into soils earlier than one month before planting to allow for residue decomposition and to avoid seed corn maggots. Heavy applications of compost or manure should also be incorporated earlier. Follow up with at least two light tillage operations to create a smooth, weed-free seedbed. The final tillage operation should be performed on the day of planting to ensure that all germinated weeds have been destroyed when the seed is placed in the ground. Seeding depth is a very important factor in an organic production system. Seeds planted too deeply will be slow to emerge, and seedlings will have immediate weed competition and a greater likelihood of damage caused by seedling diseases. A seeding depth of just one inch is sufficient on most soils and allows for rapid emergence.

Plant population is another important factor in organic corn production, especially when corn is grown on sandy soils. Plant populations should be related to the moisture-holding capacities of each individual field. In organic systems, corn plant populations per acre should be 10% higher than populations used in conventional systems. Higher plant population will increase light interception and reduce weed competition and the effects of pest damage. On soils with good-to-excellent water-holding capacity, the goal is a stand of 30,000 to 33,000 plants per acre; on soils with average water-holding capacity, 25,000 to 28,000 plants per acre; and on soils with poor water-holding capacity, no more than 22,000 plants per acre.

Narrow rows permit more uniform plant distribution and result in rapid closing of the canopy. In choosing row width, balance the potential advantages that come from narrower rows against the additional machinery cost and management that a narrow row system demands. Because cultivation is the primary weed control measure in organic production, make row widths wide enough to permit the use of a tractor-mounted cultivator. Row spaces as narrow as 20 inches have been successful under organic conditions with alterations in cultivators and guided steering systems (see text box, Chapter 10).

Corn generally requires from 120 to 160 pounds of nitrogen per acre, 30 to 50 pounds of phosphorus per acre, 80 to 100 pounds of potassium per acre, and smaller amounts of sulfur and micronutrients to obtain optimum yield. Organic corn growers should design their systems so that the amount of nutrients added to the system offsets the amount removed in the grain or forage. The local offices of the USDA Natural Resources Conservation Service, North Carolina Cooperative Extension, or the Soil and Water Conservation District can provide guidelines for a nutrient management plan. Chapter 9 in this guide also has more information on organic soil management.

Grassy weeds and warm-season broadleaf weeds, such as cocklebur and morning glory, will be among the most difficult to control. While tillage prior to planting can help reduce early-season weeds, many of the summer annuals will continue to germinate and grow. It is very important to start with a clean seedbed and to till the soil just prior to planting so that the crop begins with a head start on new weed seedlings. This will make it much easier to use cultivation to control grass and broadleaf weeds that are smaller than the corn.

It is also important to take advantage of the ability of the corn canopy to shade the soil. Shade reduces weed germination and slows their growth. Use of increased plant populations, narrower rows, row directions perpendicular to the path of the sun, and tall-growing hybrids all increase canopy density and lead to quick canopy closure.

Remember that weed competition during the first four to six weeks after planting will cause the most damage in terms of yield reductions. Weeds that emerge after canopy closure will have little effect on yield, although they can make harvest more difficult. Chapter 10 in this manual has more information on managing weeds in organic production.

Cultural practices are very important for establishing a vigorous, full corn stand. Stand establishment can greatly influence pest populations as well as crop competitiveness and tolerance to pest feeding. In fields where pests are historically abundant, do not plant organic corn if suitable, effective, and economical pest management options are not available.

Crop rotation is one of the most powerful tools for insect management and is also often the lowest-cost method of control. Rotations of at least two years and use of a non-grass crop will reduce the levels of many pests through starvation, interference with insect reproduction, or both. Rotation also gives the option of isolating corn crops from one year to the next, although this may or may not be effective for wireworm. Depending on the species, a single generation of wireworm can take one to five years to complete. As a result, multi-year rotation out of corn may be needed to avoid this pest. Rotation in large units with a minimum of 800 to 1,000 feet between current and previous corn is the most effective way to manage moderately mobile pests such as billbugs.

Cover crops may provide a benefit for reducing the abundance of some pests, while increasing the density of certain pests such as cutworms and, likely, wireworms. There is currently little information for the Southeast on pest associations with cover crops and corn.

Insect pests that feed on seed and small seedlings are typically found in the soil or at the soil surface. Populations of wireworms, cutworms, grubs, seed corn beetle, and other pests can be reduced with winter or early spring disking and the accompanying bird feeding and exposure. The combined action of these factors can give meaningful protection to planted seed and small seedlings.

Rapid germination and seedling grow-off reduces the time corn seed and seedlings are most vulnerable to insect pests between germination and the six-leaf stage, and helps the crop gain a size advantage over weeds. Losses to seedling insects and other pests can be reduced by promoting early germination through row-bedding, seeding at the recommended depth, hybrid selection for performance under cool conditions, and adequate soil fertility.

In corn, timely maturity of the crop almost always reduces insect damage. Certain pest insects and pathogens (for example, fall armyworms) reach high densities in late July and August and may severely infest late-maturing corn. Timely planting and avoidance of late-maturing hybrids (over 120 days) will reduce the level of pests attracted to the crop in late-season and prevent yield loss. When planted early, hybrids that mature in 112 days or less will usually avoid late-season caterpillar attack.

Rapid germination, early vigor, strong ear shanks, tight husks, resistance to stalk rots and other pests, strong stalks, and uniform performance over a wide population range are factors influenced by genetics that may reduce losses to insects.

Corn Billbugs

Billbugs can be serious pests of corn seedlings. No insecticide approved for organic use has activity against billbugs. Combining cultural tactics—rotation and isolation from previous corn crops—along with rapid seedling emergence and grow-off should help prevent concentrations of adult billbugs and promote rapid accumulation of tolerance. Three additional billbug management tactics are (1) avoiding areas with abundant nutsedge, which is an alternative host for billbug; (2) avoiding no-till production for organic corn because no-till soils warm more slowly and delay germination and grow-off; and (3) planting at the earliest possible date to allow seedling growth prior to billbug adult emergence.

Wireworm and Black Cutworm

In organic systems, the major tactics for reducing populations of these insects will be disc cultivation and avoidance of no-till situations. Cultural methods that promote rapid seedling growth and seeding at adequately high populations to allow some seedling loss can also be important.

European Corn Borer (ECB) and Southern Corn-Stalk Borer

As mentioned previously, the extensive adoption of Bt corn by conventional growers has decreased borer populations in corn significantly, leading to minimal issues for most organic corn growers. Their populations fluctuate greatly between years and sometimes within a single growing season, and they can still be an issue if non-Bt hosts are present in the area (for example, non-cultivated hosts in woods or wildlife areas). Organic farmers can influence the abundance of these borers through rotation, site selection (away from first-generation ECB nursery areas in potato and wheat fields), early planting, and use of short-season corn hybrids. Organically approved spinosad insecticides are labeled for ECB on corn, but they are expensive and are not likely to be effective when sprayed on tall corn. For ECB scouting procedures and thresholds, consult your local N.C. Cooperative Extension center, or the resources Scouting for Whorl Feeding Insects for scouting vegetative-stage corn and Scouting for Mid-Season Insects for reproductive-stage corn.

Western Corn Rootworm

Western corn rootworm is a pest only in non-rotated corn. It can be successfully managed in an organic system by rotating corn with other crops.

Three key diseases—seed rots and seedling blights, stalk rots, and charcoal rot, which are usually controlled in conventional systems either by fungicides or management practices—can have significant impacts on organically grown corn. Growers should be aware of these diseases and select hybrids and management practices that reduce the risk they pose. While there are many other diseases that can attack corn, they rarely cause economic loss. Pictures of these field corn diseases can be found on the Cornell CALS Field Crops website.

Seed Rots and Seedling Blights

Seed rots and seedling blights caused by species of Fusarium, Stenocarpella, Pythium, and other fungi are often associated with the term “damping-off,” when plants die at emergence or within a few days of emergence. These diseases are more prevalent in poorly drained, excessively compacted, or cold, wet soils. Planting old or poor-quality seed with mechanical injury will increase seed rots and seedling blights, as will planting seed too deep in wet, heavy soils. Seed vigor ratings are often used to select hybrids with genetic resistance to seed rots and seedling blights.

Stalk Rots

Stalk rots (caused principally by the fungi Stenocarpella maydis, Fusarium spp., and Colletotrichum graminicola) are present each year and may cause considerable damage, particularly if abundant rainfall occurs during the latter part of the growing season. Stalks previously injured by cold, leaf diseases, or insects are especially susceptible to attack by these fungi. Diseased stalks ripen prematurely and are subject to excessive stalk breaking. Stalk rots not only add to the cost of harvesting but also bring the ears in contact with the ground, thereby increasing their chance of rotting. Adequate fertility (particularly adequate potassium) is key to controlling stalk rot.

Charcoal Rot

Charcoal rot (caused by the fungus Macrophomina phaseolina) becomes most evident with the onset of hot dry weather. It may cause stalk rot, stunting, or death of the corn plant. This disease is often considered to be stress related. Typically, when this disease occurs in North Carolina, soil fertility and pH are at very low levels. Although the fungus survives in the soil, rotation is not generally helpful since most crops are susceptible to this disease. Supplying adequate nutrition and water is the principal means of control. Hybrid resistance in corn has not been documented.

Early harvesting usually avoids crop damage from pests or hurricanes and prevents field losses resulting from ear drop and fungal pathogens. Probably the most important reason for timely harvest is the potential for yield reductions resulting from ear loss and ear rots due to stalk lodging, ear drops, and reductions in kernel weight. Fungal diseases that infect the corn kernel also cause more problems as harvest is delayed. Mycotoxins, such as aflatoxin and fumonisin, which are produced by fungal pathogens, also increase as harvest is delayed and may result in corn that is unsuitable for human or livestock consumption. Ideally, corn harvest should begin as soon as the grain reaches moisture levels of 25% or less. Under favorable conditions, corn should be ready to harvest in 10 days or less following the black layer formation at the base of the kernels.

Hybrids

Crops that are propagated by utilizing the pollen from selected (usually inbred) male plants to fertilize selected (usually inbred) female plants are called hybrids. Neither the female or male plants may exhibit robust growth or vigor when grown. Yet, when these plants are crossed they may exhibit vigor, resistance to disease or drought, or other desirable characteristics. Probably the most common hybrid crop plant today is corn. Hybrid corn seed is produced by allowing male plants to have tassels to produce pollen. Tassels are removed from the female plants and pollination takes place by the male plants. The resulting seeds contain a mixture of genes from both parents at each point on the chromosome. Since the two parents are inbreds that carry the same genes at each point on their chromosomes (homozygous), the resulting hybrid exhibits the same characteristics (such as height, color, and ear placement) across the seed lot. This gives the crop its uniformity and makes it easier to handle and harvest.

Open-Pollinated (OP) Crops

This is the term given to crops that are not hybrids and where seed is produced by the crop pollinating itself. Some of the most common OP crops are soybeans and wheat. In the corn industry, most of the crop seeds produced 75 to 100 years ago were OP types. Today, there is a thriving niche seed business in "old or antique'' varieties, nearly all of which are OP materials. However, crops originating from OP seed stock alone have not necessarily undergone serious breeding efforts through isolation, inbreeding, crossbreeding, or other means of genetic manipulation. Unlike OP soybeans and wheat, which are largely self-pollinating, OP corn exhibits a large degree of cross pollination (pollen from one plant fertilizing another). This means that most OP corn varieties are not homozygous with similar genes at each point on the chromosome. Instead, OP corn exhibits mixtures of genes (heterozygous) at each chromosome similar to a hybrid. However, unlike a hybrid, where each parent is identical and imparts identical mixtures of genes to the offspring, OP corn parents differ in their genetic makeup, with the result that the offspring exhibits a wide range of characteristics, such as significant variations in height, maturity, ear placement, and kernel color. This is often undesirable as it increases difficulty in managing and harvesting the crop.

The Problem with Saving Hybrid Seed

As stated earlier, hybrid seed has a mixture of genes from each parent at each of its chromosomes (Alleles). The only saving grace is that because the parents were homozygous, each seed has the same mixture. However, when hybrid seed is saved, it is no longer possible to control which plant contributes the male genes and which contributes the female genes. Therefore, saved hybrid seeds are genetically different from each other. When these seeds are planted again, different genes start to express characteristics (such as height and kernel color) that differ from each other. One fourth of the seeds will look more like its female parent, one fourth will resemble the male parent, and the remaining half will have a combination of characteristics of both parents. This segregation of genes means that hybrid seed will start to have the same problematic issues that OP varieties have, such as a range of maturity, height, and color, which make harvesting and managing the crop more difficult.