Begin Scouting For Western Bean Cutworm

According to Rick Foster, an entomologist at Purdue University, western bean cutworm (WBC) is a relatively new pest to sweet corn growers in Indiana and Michigan. (Click here for more information on sweet corn pests.)

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Corn growers, in general, are encouraged to begin scouting in late July for signs of WBC. First found in Indiana in 2006, western bean cutworms feed on corn, legumes, and dry beans, such as kidney and black beans. Despite the name, they do not feed on soybeans.

The cutworms can be identified by the black rectangles that develop behind the head of the later instars. These are commonly found feeding within the ear in late summer.

WBC populations are tracked and roughly estimated each year using pheromone traps placed throughout the state. The traps capture the grayish-white moths, which usually lay eggs on Indiana corn plants in July. Feeding damage can appear a few weeks later.

So far this year, moth captures in northern Indiana are lower than previous years, said John Obermeyer, Purdue Extension entomologist and Indiana trap coordinator. But the number of moth catches does not necessarily give entomologists an accurate number of larvae, and is generally used as a presence or absence tool to initiate scouting.

Larvae begin emergence after a period of warm weather, but extreme conditions, such as last year’s drought and excessive heat, are hard on WBC. With the cooler, wet Indiana spring this year, Purdue Extension entomologist Christian Krupke said the insects are likely delayed.

“We’ve had a cool spring, so we’d expect emergence a little later than last year,” he said. “It is likely that the hot, dry weather that we had last year was not good for them.”

In the early stages of development, western bean cutworms feed on pollen caught in leaf axils of corn plants (where the leaf meets the stem). This is when growers should apply insecticides to fields to prevent further damage. Once the cutworm is inside the husk of the corn plant and begins feeding on kernels, insecticides are no longer effective. When pollen is gone, kernel feeding will begin and continue until the first frost.

Click here for more information about western bean cutworm scouting.