Western Bean Cutworm

Bryan Jensen, UW Department of Entomology and Division of Extension

Western Bean Cutworm adults are well into flight in southern Wisconsin and it is a good time to be scouting for eggs. Foliar treatments are suggested with 5% of the plants have egg masses. On whorl stage corn the best timing is to spray is when egg masses are dark colored. Indicating hatch will start soon.

When given a choice, adult females prefer pre-tassel corn to lay eggs because pollen is an important food source for larvae prior to moving to the ear. Infestations are often aggregated within a field so thorough field scout is needed. Go to at least 5 different areas of a field and count egg masses on 20 consecutive plants. Often eggs are found on the upper leaf surface on the uppermost leaves. Use the sun to backlight those leaves and look for the shadow of the egg mass. Later during the adult flight, also look for larvae that may have already hatched. Often, they are found in leaf axils feeding on pollen.

Western bean cutworm egg mass near/at hatch. Egg mass turns from cream colored to purple 24-48 hours before hatch. Newly hatched larvae consume the egg shell, so egg masses are most evident before or immediately after hatch.
(Photo: E. Cullen, Univ. of Wisconsin-Madison)