Proper management reduces yield losses from corn insects

Corn producers face substantial economic losses from insects every year. In Texas, at least 25 insect pests attack corn at one or more of the four major growth stages: seed/seedling, whorl to pre-tassel, tassel/silk, and grain filling.

Pests that attack at the respective stages include wireworms, southwestern corn borer, corn earworm, and spider mites.

“Entomologists have found that producers should have an integrated pest management (IPM) program to control insects expeditiously,” says Patrick Porter, Texas Extension entomologist at Lubbock. “This plan has four components: prediction, prevention, detection (scouting), and remedial action. Carrying out the first three often eliminates the need for the fourth.

“Prediction involves anticipating problems before they occur. Experienced producers often can predict pest problems based on weather, the cropping system used (such as no-till or conventional tillage), and past pest problems,” Porter said. “Also, computer models predict pest outbreaks.”

Prevention is often the least expensive and most effective way to save money on pest management. Techniques include crop rotations, planting dates, sanitation to destroy insects and their non-crop habitats, planting resistant/transgenic varieties, preserving beneficial insects, and using adequate levels of fertilizer and water.

Scouting is a prerequisite to successful pest management.

“Corn should be scouted at least weekly, and more often when pest numbers are increasing,” Porter said. “Also, pesticide-treated fields should be scouted as soon as the re-entry interval has passed, because applications are not always effective.

“Scouts should routinely check for pest insects, beneficial insects, diseases, weeds, plant nutrition problems, and water stress,” Porter said. “This information is essential for making sound management decisions.”

Also, scouts should know which insects are most likely to become a problem as this will make efforts more effective. Examples: Many cutworm species lay eggs on weeds before corn is planted, and European corn borers prefer to lay first-generation eggs in taller corn. Armed with this knowledge a scout can locate the initial site of infestation more effectively and then track the insects as they begin to spread out.

“Fields should be sampled adequately because significant variations in pest counts can result from plant differences caused by soil type or fertility, drainage, organic matter, and weeds,” Porter said.

Differences in pest counts between locations within a field can be a function of the pests themselves. Some pests tend to remain clumped in specific areas, particularly if infestation level is low. With other pests, infestations may begin on the side of the field from which the prevailing winds blow and then spread downwind through the field.

Remedial actions—pesticide applications—lower the number of pests. “These should be used judiciously because broad spectrum pesticides destroy both beneficial insects and pests, and can result in resurgence of the treated pest and outbreaks of other pests,” Porter said.

“Also, pesticide applications should not be used until the cost of the pest damage equals or exceeds economic threshold—pest density that justifies pesticide applications, factoring in costs and the amount of damage pests will do if untreated.”

There are two major types of economic thresholds, static, and dynamic. Static models do not change to reflect actual values and costs; dynamic models do. “Neither type is perfect but both are usually fairly accurate,” Porter said.

“Economic thresholds are only guidelines. However, they are reasonably good indicators of when control measures should be implemented, but there are no hard and fast rules in integrated pest management. It is a blend of science, art, and experience.

“Making integrated pest management decisions can be difficult, but information to help is available from county Extension agents, agricultural consultants, and agribusinesses,” Porter said. “And if the producer anticipates a significant economic loss due to insect pests, he may want to enlist the aid of a professional scout/consultant.”

Detailed information on corn insects and integrated plant management is available in AgriLife Extension publication B-6177, Texas Corn Production, Emphasizing Pest Management & Irrigation: 2006, on website, Agricultural Insects. Printed copies are available from Texas AgriLife Extension at

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Additional information about integrated pest management of corn is available on website

TAGS: Corn
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