2005 Year in Review

From the Fields Western Bean Cutworm

Source: Jim Morrison, Extension Educator, Crop Systems, Rockford Extension Center, University of Illinois, 417 Ware Avenue, Suite 102, Rockford, IL 61107, Phone 815/397-7714, Fax 815/397-8620, email: morrison@uiuc.edu

Since July 1, western bean cutworm moths have been captured in pheromone traps in eight Illinois counties: Adams, Lee, Mercer, Rock Island, Warren, Whiteside, Will, and Winnebago. What does this mean?

Cornfields in those counties need to be scouted, especially those that are tasseling or near tasseling. This holds true for other counties as the pest is detected.

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 pest was detected in Illinois for the first time last summer in Warren County.

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.

In corn, the eggs are laid on the upper surfaces of leaves by the female moth. As the eggs develop they turn from white to tan, then dark 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 overwintering chamber. The insect spends the winter in the prepupal stage.

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. If larvae have hatched, apply an insecticide after 95 percent of the tassels have emerged, but before the larvae enter the silks. Control is more difficult after the larvae have moved to the silks. If the larvae have not hatched and corn plants have tasseled, time the insecticide application to coincide with the hatch of the larvae. As mentioned above, if the eggs are purple, hatch will normally happen in about 24 hours.

Additional information is available at Extension offices, in the 2005 Illinois Agricultural Pest Management Handbook, and in the Western Bean Cutworm Factsheet available at Integrated Pest Management

by  Editor, theCity1.com
July 18, 2005