By SHELLY STRAUTZ-SPRINGBORN
Michigan Correspondent

LANSING, Mich. — Western bean cutworm (WBC) is making a stronger stand in Michigan this growing season; it is a severe pest in corn and dry beans, which affects both crop yield and quality.

Chris DiFonzo, Michigan State University field crops entomologist, said it has been detected throughout much of the state this year.
“We had infestation last year in the northwestern quadrant, from Oceana County to Montcalm County and north,” she said. “This year, we have had detections all across the state and into Ontario, Canada.”

Historically, WBC was a pest in the western Corn Belt. DiFonzo said it has steadily spread from west to east, and has “moved very rapidly across the Corn Belt in the last 10 years.”

Unlike other cutworms, WBC is a late-season pest. It feeds primarily on corn ears, chewing and scarring kernels, and predisposing the ear to fungal and mold infections. One generation of WBC occurs each year.

Moth emergence usually begins in early July. After mating, females lay eggs on available host plants such as field corn, sweet corn, popcorn or dry edible beans. Typically, the pest is attracted to fields in which corn is tasseling or near tasseling and fields that have hybrids with upright leaf characteristics.

After hatching, larvae feed on host plants for about 31 days. After a larva finishes feeding and completes development, it drops to the ground and burrows into the soil, where it overwinters.

“It’s pretty much done for the season,” DiFonzo said. “It’s ready to pupate. In a couple of weeks, they will drop and go into the ground for the winter.”

During years with severe infestations, multiple larvae per ear may be common. “It is very happy with its brothers and sisters,” she said. “You can see that in heavily infested ears. There’s six, eight, 10 of them on an ear.”

Under severe feeding pressure, 50-60 percent of an ear’s kernels may be damaged. In dry edible beans, eggs are laid in areas of dense bean foliage on the lower surface of leaves. Dry beans are particularly attractive to WBC if neighboring cornfields have already tasseled.

Larvae chew holes in pod walls and developing seeds. Most feeding occurs on cloudy days or at night. If WBC development is not complete, as beans are pulled, larvae may congregate under the windrow, feeding on pods and seeds until harvest.

In corn, DiFonzo said, “there is some thought that with the greater planting of Bt corn, we have cleared up the ears so there is not a lot of corn borer.” That characteristic may have made corn more vulnerable to WBC.

“What we see is that some types of Bt corn control this pest and some do not,” she added. “The type that does is Herculex. It may not be 100 percent control, but it is probably as effective as if you were spraying for corn borer.”

DiFonzo said infestation can be managed with insecticides, “but the timing has to be right.” Plus, she said spraying can be more difficult because infestation occurs late in the season, when corn is taller.

“Farmers have to have the right equipment, which may be a challenge,” she said.

Overall, DiFonzo said the pest is “sporadic,” and she doesn’t believe it will be a pest every year.

“The moth prefers to colonize fields that are pre-tassel,” she said. “The moths choose the favored fields to land in. Across the landscape, if you have fields that are in the acceptable stage where the moths are flying, they may or may not land.

“Different farmers are going to have different risk.”