Entomologist Suggests Corn Growers Consider Pest Issues Before Planting

Kansas enjoyed a mild, albeit dry winter through much of the state, but that doesn’t necessarily mean farmers will see more insects in their corn this year, a Kansas State University entomologist says.

"Populations of most below-ground insects, such as wireworms and white grubs, probably were not greatly affected," says Randy Higgins, field crop entomology specialist with K-State Research and Extension.

The mild winter may have an impact on other insects, however. Higgins provided the following information on several pests common in Kansas cornfields:

• Black cutworms – The generally accepted theory is that most of these insects enter the state as egg-laying adults from southern regions. So, problems depend on how many invade Kansas and whether the female moths find conditions suitable for egg laying and larvae survival.

  Weed cover at or before planting can lead to increased cutworms because egg-laying female cutworm moths are attracted to weeds. But, moths must move through an area and find a field before laying eggs on a favorable site. If this happens and large numbers of cutworms start feeding on the weeds, problems in the crop could develop, particularly if a tillage operation or a burn-down herbicide eliminates the weedy food source before they have finished feeding.

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• Flea beetles – Adults overwinter in grassy or brushy areas. Survival depends on winter conditions, including temperatures, so producers should watch for these insects, paying attention to the earliest emerging corn.
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• Spider mites – These mites overwinter in such vegetation as brome and sometimes alfalfa and other cover crops. A mild winter can mean greater numbers at the start of the growing season, but factors can interfere weeks or months later with the development of large populations. Seasonal conditions and mite predators will help determine the seriousness of future populations.
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• European corn borers – These pests overwinter as large larvae inside stalks of non-Bt corn. Field-to-field movement and mixing of the population occur after the adults emerge. Storms during mating and egg laying may possibly influence the significance of future problems more than the borers´ success in surviving the winter.

Cultural practices such as rotations also can have an influence on insect pests expected to be of concern in this year´s cornfields, Higgins said. If corn is planted after a non-corn crop, for example, rootworms should not be a problem, although other pests could still be a concern.

Rootworms lay eggs in the soil during the late summer and fall, he explained. In Kansas, they prefer to lay their eggs in existing cornfields. As a result, when a grower rotates to another crop, rootworm larvae emerging from eggs laid in last year’s corn ground should starve, because suitable food sources are unavailable.

Fortunately, Kansas does not yet have the strain of rootworm that prefers to lay many eggs in nearby soybean or other non-corn fields. That problem occurs in some eastern and northern U.S. corn production regions, Higgins said. Growers there may be treating for rootworms every year, regardless of their rotation schedule.

In contrast, wireworms and grubs seem to be more of a problem when corn follows some type of grass or sod. But, where corn follows corn, rootworm protection of some type is often justified unless the field was scouted last year and low levels of rootworm adults were present – which means low egg laying potential and relatively low populations of larvae will be present. Paying for additional protection also may not be justified where moderate to high adult rootworm populations were developing last year, but timely and effective adult control treatment was applied. If frequent scouting through the end of the egg laying period showed the egg-laying adult population did not rebound to threatening levels through immigration from surrounding fields, treatment this year may be unnecessary.

Growers can refer to the K-State Research and Extension "Corn Insect Management 2006" recommendations, publication MF-810, for information on seed treatments, planting time insecticides, post-planting rescue and foliar treatments, and host plant resistance (including the use of BT corn) as insect management tools. This publication is revised annually and is available on-line at www.oznet.ksu.edu/library/. Printed copies can be picked up at most county or district K-State Research and Extension offices.