Pests attacking corn crops, often generalized as “corn flies,” threaten the harvest. Keeping them away requires a comprehensive, proactive strategy. Effective crop protection involves managing the environment and understanding specific prevention and removal methods. Success relies on integrating diverse control methods, from initial exclusion to targeted treatment.
Identifying the Primary Corn Pests
The term “corn flies” refers to several damaging pests, including true flies and caterpillar pests (moths). Seedcorn Maggots are the larvae of a small, gray fly that targets corn seeds shortly after planting. These legless, yellowish-white maggots burrow into the seed, destroying the germ and causing poor stand establishment or “snakehead” seedlings. This damage is most severe in cool, wet soil conditions that slow germination.
The Frit Fly is a tiny black insect whose larvae tunnel into the central shoot of young plants. This feeding causes the “deadheart” symptom, where the central leaf turns yellow and can be easily pulled out, often killing the plant. The Corn Earworm, an adult moth, is a notorious pest whose larvae feed directly on developing kernels at the tip of the ear. These caterpillars enter through the fresh silks, contaminating kernels with frass and often leading to secondary fungal infections.
Cultural Practices and Exclusion Methods
Proactive cultural practices are the first defense, making the corn patch less appealing to egg-laying pests. Rotating corn with a non-grass crop, such as a legume or vegetable, is effective against ground-dwelling insects like the Seedcorn Maggot. Rotation breaks the pest’s life cycle by eliminating a host source.
Sanitation is important because the adult Seedcorn Maggot fly is attracted to fresh organic matter, such as recently incorporated manure or green cover crops, for egg-laying. Avoid planting corn immediately after tilling in fresh residue; allow time for the material to decompose. Planting date manipulation manages the migratory Corn Earworm. Planting corn early ensures the silking period is complete before the pest’s peak flight period in late summer (August and September).
Physical exclusion offers an effective barrier against early-season flying pests. Lightweight row covers, which allow sunlight and water to pass through, can be placed over the corn immediately after planting. This barrier prevents adult flies from laying eggs on the seedlings or in the soil. The row covers must be secured tightly along all edges and removed before the corn begins to tassel to ensure proper wind-pollination.
Targeted Non-Chemical Controls
Once pests are detected, non-chemical controls offer targeted treatment options that minimize environmental impact. Pheromone traps use synthetic sex pheromones to attract male moths, primarily for monitoring pest populations like the Corn Earworm and European Corn Borer. Monitoring the daily moth count helps determine the action threshold for when control measures are necessary.
Organic microbial insecticides are an effective approach against caterpillar pests. Bacillus thuringiensis (Bt) is a naturally occurring soil bacterium toxic only to caterpillars that ingest it. For Corn Earworm control, Bt products must be mixed with a food-grade oil carrier (like corn or soybean oil) and applied directly to the fresh silks. This oil-based application ensures the product penetrates the silk channel, providing a lethal dose to newly hatched larvae before they bore into the ear.
Bt has a short residual effect, requiring re-application every three to five days, or after heavy rain, to maintain a protective barrier on the continuously growing silk. For pests that feed in the corn whorl, such as the European Corn Borer or Fall Armyworm, the Bt spray must be directed into the whorl to reach the feeding larvae. Botanical insecticides, like Neem oil, act as a repellent and feeding deterrent against various pests, including aphids and earworms.
Strategic Insecticide Application
Chemical intervention should be a last resort, used only when pest populations exceed economic thresholds that forecast significant yield loss. Synthetic insecticide effectiveness depends on precise timing and application, as most pests hide inside the plant structure. For caterpillar pests like the European Corn Borer and Fall Armyworm, insecticides must be directed into the plant’s whorl before the tassel emerges to coat the interior leaves where larvae are feeding.
Controlling Corn Earworm requires targeting the silks, the larvae’s entry point to the ear. Sprays should begin as soon as fresh green silks appear and continue until the silks turn brown, indicating pollination is complete. Timing the application approximately 48 hours after pollination can increase kernel production and reduce the risk of interfering with fertilization.
Pollinator safety is a major concern because corn tassels release pollen over several days. Although corn is wind-pollinated, pollinators may forage on flowering weeds within the rows. To minimize exposure, all foliar insecticide applications must be performed late in the evening (typically 6:00 PM to 7:00 PM) or very early morning. This timing ensures the spray residue has dried and the product’s short-term toxicity has dissipated before honey bees and other pollinators begin foraging.