Photo by Jeanne Falk Jones, K-State Research and Extension. Western bean cutworm egg mass, found on upper corn leaf surface near the stalk.
Western bean cutworm adults have begun laying eggs and some of those eggs have begun to hatch. Here’s what you need to know. WBC moths lay eggs in clusters of 5 to 200 on the top surface of the upper third of the corn plant, near the whorl. Eggs develop over a 5-to-7 day period and the egg color changes from cream-tan to purple just before hatching. Newly-hatched larva feed on corn tassels before migrating to the silks and ears. A month into their development, they drop to the soil surface and burrow up to six inches deep, remaining there through the winter until emerging as adults the following June.
To scout for WBC, Kansas State University agronomists recommend checking 20 plants in a minimum of five different areas of each field. Look for eggs on the top surface of the upper-most leaves and larvae in the tassel.
When making treatment decisions for WBC, understanding the threshold of the insect is important. Corn hybrids without Bt control of WBC benefit from an insecticide if 5-to-8 percent of the corn plants have egg masses or larvae. Application timing is important and should occur when 95% of the corn plants in a field have tasseled. If larvae have migrated from the tassel to the ear, they will be protected by the husks and control will be ineffective. When considering fungicide applications, work closely with your AgVenture Yield Specialist to determine the best tactical approach for your fields.