Organic Insect Pest Management: Field Corn
By: John Van Duyn, Entomology Extension Specialist, NCSU
Major Corn Insect Pests and Management
Cultural practices are very important in establishing a vigorous, full corn stand, and for influencing pest populations, crop competitiveness and pest tolerance. The following cultural practices can be used to produce a vigorous and competitive corn crop that can tolerate insect pest feeding.
Crop rotation: Crop rotation is the most powerful tool for insect management and is often the lowest cost tactic. Rotation with a non-grass crop reduces the levels of many pests through starvation and/or eliminating insect reproduction. Also, rotation gives the option of isolating this year’s corn from last year’s corn. Rotation may be yearly or in multiples of years depending on the pest problems of a particular locale and crop combination. For best results, a rotation of at least two years is needed, especially on organic soils or where billbugs, western corn rootworm, and other yield decline factors are common if corn follows corn. Rotational patterns are also important to the management of moderately mobile pests, such as billbugs. In this case, rotation in large units with a minimum of 800 to 1000 feet distance between last year's corn and this year’s corn is most effective.
Soil and agronomic considerations: Optimal soil pH and fertility are essential to vigorous plant growth and high yield capacity, which can be critical to the crop's ability to perform in the presence of pests. Likewise, fields with drainage limitations, soil pans and other barriers can suffer from low plant vigor and increased susceptibility to pests. Avoid planting fields with problems that limit crop growth and health as poor plant competitiveness affects pest tolerance. Control of insects with tillage: Seed- and small seedling-feeding insect pests are typically found in the soil or at the soil surface. Wireworms, cutworms, grubs, seed corn beetle, and other pests are affected by winter or early spring disking and the accompanying bird feeding and exposure. Residue on the soil surface provides protection for these pests and many insects overwinter in the soil. Damage to corn seed and small seedlings is greater in no-tillage or minimum tillage culture versus conventional tillage. Typically, early spring disking destroys this cover, brings many pests to the surface, and attracts large numbers of birds. The combined action of these factors disrupts potential pests populations and can give meaningful protection to planted seed and small seedlings. In organic corn production, caution should be used with no-till culture, especially in areas where southern corn billbug, wireworms, and black cutworm are common.
Rapid seed germination and seedling grow-off: Corn plants are most vulnerable to insect injury when seed are swelling and sprouting and when seedlings are small. Insects can easily kill germinating seed and seedlings. Those seedlings suffering early insect injury may fail to have an ear or otherwise be less productive plants. Rapid germination and seedling grow-off reduces the time corn seed/seedlings spend in the most sensitive stage (from germination to the six leaf stage) and helps the crop gain a size advantage over weeds. Therefore, attention to factors that promote early germination (such as row-bedding, seeding at the recommended depth, and hybrid selection for performance under cool conditions) can reduce losses to seedling insects and other pests.
Avoiding serious insect infestations: Corn should not be planted in fields where pests are at high levels if suitably effective and economical pest management options are not available. This is especially true in billbug and western corn rootworm infested areas (chiefly in the lower coastal plain and Piedmont/mountains, respectively), where current-season fields should be isolated at least 800 to 1000 feet away from corn fields of the previous season.
Crop maturity: In corn, timely maturity of the crop almost always reduces insect damage. Certain pest insects and pathogens reach high levels in late July and August and may severely infest late maturing corn. For example, late season corn borers and fall armyworm, that are often very abundant, are attracted by green, immature plants but will not infest mature plants. Timely planting and avoiding late maturing hybrids, such as 120 + day maturity hybrids, will reduce the level of pests attracted to the crop in late season and yield loss. Hybrids maturing in 112 days, or less, will usually avoid late-season caterpillar attack if planted early.
Hybrid selection: Hybrids vary in their ability to withstand insect pests, as well as their attractiveness to some pests, such as European corn borer. 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 all factors, influenced by hybrid genetics, that may influence losses to insects. Seedling insects, stalk borers, and ear feeding insects are most influenced by hybrid traits. Some hybrids have European corn borer resistance traits that will reduce hybrid susceptibility to this important insect.
Plant population: A farmer's goal is to end the season within the recommended plant population for each hybrid planted. The level of plant loss due to pests that can be tolerated without economic impact is related to the population level initially established. Plants lost to insects are not important to yield, but the remaining plants are. Typically, a field with minimal pests and other problems will have no more than 90% as many plants as the initial seeding rate. Modern hybrids can compensate for some plant loss before yield begins to decline, under favorable growing conditions. A 10% plant loss from a full seedling stand will usually not noticeably affect yield. When planting, the grower should assure that the full recommended seeding rate is used if seed/seedling insects are anticipated. In this event, using a seeding rate of at least 10% above the maximum recommended seeding rate will increase the crop tolerance to seedling loss.
Major Corn Insect Pests and Management
Southern corn billbug: Billbugs can be serious pests of corn seedlings. No organically approved insecticide is available that has activity against billbugs. The combined effects of cultural tactics are designed to avoid concentrations of adult billbugs (rotation with isolation), and to promote rapid accumulation of tolerance, through rapid seedling emergence and grow-off. Most of the cultural methods, mention above, apply to billbug management. Three additional tactics are: 1.) avoiding areas with abundant nutsedge infestation, since this group of plants are alternate hosts for billbug; 2.) not using no-till, since soils warm more slowly; 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 insect reducing tactic will be to disc-cultivate, as described above, and to avoid no-tillage situations. Also, cultural tactics that promote rapid seedling growth and seeding at adequately high populations, to allow some seedling loss, can be important.
European corn borer and southern cornstalk borer: Borers occur in all NC corn fields. Their populations fluctuate greatly between years and sometimes within a single growing season. The organic producer can influence the abundance of these borers through rotation, site selection (away from 1 st generation ECB nursery areas of white potato and wheat fields), early planting, using short season corn hybrids, and selecting corn hybrids with ECB tolerance. These actions will help avoid high populations, in space and time, and tolerate those borers that do occur. Organically approved spinosad insecticide is labeled for use against ECB on corn, but this will likely not be effective when sprayed to tall corn and may be prohibitively expensive. If ECB scouting procedures and thresholds are desired, please consult the following web site: http://www.ces.ncsu.edu/plymouth/pubs/ent/index1.html or your county Extension office.
Western corn rootworm: Western corn rootworm is only a pest in non-rotated corn and can be successfully managed in an organically certified system by rotating corn with other crops.
There are a number of insecticides approved for use in certified organic production systems—mainly non-synthetic compounds or biocontrols. These include: neem (and its derivatives), Bacillus thuringiensis, Beauvaria spp., diatomaceous earth, Pseudomonas, pyrethrum, spinosad, and Trichoderma. While these products do have potential for controlling insect pests in corn, no research has been done on them in field corn in North Carolina and, therefore, we can give no recommendations for their use in the state. The cost of organically approved pesticides may be prohibitively expensive for field crop production. Conditions for use of a pesticide must be documented in the organic system plan (NOP 2000). See the Pest Management Web Resources for more information, or check out the OMRI site.
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