Western Bean Cutworm Officially a Pest of Indiana, Michigan

Insect hits cornfields in two new states as it continues to expand its movement into the Eastern Corn Belt

INDIANAPOLIS — September 19, 2007 — When Larry Lathwell decided to take a look at the progress of his drought-stressed corn in early August, the Frankfort, Mich., farmer discovered he wasn’t the only one in his cornfield that day. As he pulled back on the husks, ground kernels fell out until a shredded ear of corn was revealed with several worms feeding on it. Each ear of corn he inspected looked the same.

“I thought perhaps it was corn earworm,” Lathwell said. “But when I saw we had eight to 10 worms on some ears, that didn’t seem like earworm to me because they are cannibalistic.”

When his seed salesman identified it as western bean cutworm (WBCW) — which was later confirmed by Michigan State University extension — Lathwell was quite surprised.

“That really threw us off because we had never heard of western bean cutworm before,” he added.

Those in the ag industry following the movement of this insect are not surprised by the latest find. In the last decade, WBCW has moved from the dry bean fields of western Nebraska into eastern Nebraska and throughout Iowa. Within the last two years, WBCW crossed the Mississippi River and became a pest of cornfields in northern Illinois and southwestern Wisconsin.

After capturing WBCW moths the past two years in Indiana, Purdue University entomologists confirmed in August that they had identified western bean cutworm larvae in a Jasper County cornfield, located in northwestern Indiana, officially marking WBCW as a pest of Indiana.1

“The larvae will overwinter in the soil in the pre-pupal stage, emerge as moths and take flight next summer before laying eggs at the top of corn plants. When the eggs hatch, the larvae quickly move down the plant to the ears and begin feeding under the protection of the husks,” said Dr. Mike Culy, U.S. technical leader for Dow AgroSciences. “While you can’t predict which cornfields they’ll infest, they will inflict considerable damage when they arrive.”

Gary Lathwell, Larry’s brother, can attest to the damage he’s seen, adding that corn growers throughout Benzie County saw their fields infested by WBCW.

“Our ears aren’t very big this year because of the drought we’ve experienced, but they’re eating everything,” Larry Lathwell said. “Some ears we saw in the field, the corn was totally gone and you’d still find a worm trying to bore into the cob looking for something to eat. We’re consistently seeing three, four, five or six worms to an ear and it looks like in some places, the crop is going to be a total loss.”

Insecticides can control WBCW; however, the window of application is narrow. Once larvae hatch, they quickly get to the cob. The husks provide protection and cover from the insecticide. Farmers need to proactively scout fields to see whether they have a WBCW infestation. Usually, WBCW isn’t detected until it’s too late.

A better way to protect corn from WBCW damage is with an in-plant trait. Farmers who grow corn hybrids with HERCULEX® Insect Protection (www.HERCULEX.net) in-plant traits have built-in protection against WBCW; however, YieldGard® and Agrisure™ in-plant traits do not offer this protection.

Garry Lathwell says his corn that was infested with WBCW contained hybrids with YieldGard Corn Borer and YieldGard Rootworm in-plant traits.

“At this point, it’s not feasible to spray it,” he said. “We’re going to go with HERCULEX next year. There’s no way I can afford this type of damage. While I realize it wasn’t going to be a great crop, by the time they’re done eating, we’re looking at a loss of 50 percent to 60 percent.”

It’s likely that WBCW will continue to be a pest of growing economic importance across the Corn Belt, Culy adds. He says a 40 percent yield loss is not uncommon, and even a 5 percent loss can cost a grower $25 per acre at today’s corn prices where yields run about 175 bu./A.

“One of the theories discussed today is that the increased use of in-plant insect protection as a whole are helping suppress populations of corn earworm, which are cannibalistic and can help control populations of western bean cutworm,” Culy said. “So far, we see the area that western bean cutworm infests continuing to grow. Since HERCULEX is the only in-plant trait that offers protection against western bean cutworm, we’re seeing more demand for it.”

You can learn more about WBCW by viewing a slide show from Iowa State University extension.

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