2005 Year in Review

Western Bean Cutworm

As if soybean rust, western corn rootworm, and perhaps soybean aphid weren’t enough pests to contend with, farmers and agriculture dealers need to be aware of a new insect in 2005. Western bean cutworm was detected in Illinois (Warren County) for the first time last summer.

Historically, the western bean cutworm has been a pest in the western cornbelt and over the last few years it has moved east across Iowa.

The larva of the insect feeds on both corn and dry beans, affecting both yield and quality of the crop. Unlike cutworms, the western bean cutworm is a late-season pest of corn feeding mainly on the ears, predisposing them to disease infections.

Generally, only one generation of the western bean cutworm occurs yearly with moth emergence beginning in July. Eggs are laid on corn or dry edible field bean leaves. In corn, the eggs are laid on the upper surfaces of leaves. As the eggs develop they turn from white to tan, then purple within about 24 hours of hatching. After hatching, the larvae pass through five instars and feed on host plants for about 30 days.

When larvae develop to the third instar, they have three dark stripes just behind the head. This characteristic helps differentiate the western bean cutworm from other caterpillars feeding in cornfields.

Newly hatched larvae move from the leaves to the corn whorls and then to the silks. As the larvae and corn ears develop, the larvae begin feeding on ear tips. An ear may be infested by more than one larva. After a larva finishes feeding and development, it drops to the ground and forms a subterranean over wintering chamber. The insect spends the winter in the prepupal stage. In May, western bean cutworms pupate and emerge as adults in July.

Scouting for western bean cutworm should begin in mid-July. Check 10 consecutive corn plants in at least five random locations in the field. Look for egg masses or small larvae on the upper surfaces of corn leaves. Also, check tassels for larvae before pollen shed.

An insecticide treatment is suggested if eight percent of the plants have egg masses and/or small larvae. Timing of an insecticide application is critical. Control is more difficult after the larvae have moved to the silks.

Additional information is available at Extension offices and in the 2005 Illinois Agricultural Pest Management Handbook.

by  Editor, theCity1.com
March 4, 2005