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Corn+Soybean Digest

Arriving Corn Pest An Earful Of Bad News For Farmers

The western bean cutworm (WBC), which attacks maturing corn, has migrated into Indiana from Illinois and states further west, says Christian Krupke, Purdue University Extension entomologist. While the pest isn't expected to cause crop damage this year, corn growers will want to keep an eye on the insect from now on.

"The western bean cutworm is a moth in the same family of moths as the corn earworm," Krupke says. "In fact, it could be confused with corn earworm because the western bean cutworm is also a late-season pest that feeds on corn ears.

"One key difference between the two pests is that you can have more than one western bean cutworm larvae on an ear of corn, whereas the corn earworm is cannibalistic so you'll only have one corn earworm larvae per ear. So at least from that standpoint, you have the potential for more damage with the western bean cutworm."

Based on WBC feeding in Iowa and Nebraska, yield loss of a few bushels per acre is possible, Krupke says.

Purdue Extension specialists have been monitoring the insect's eastern migration. This year they began capturing WBC moths in traps set across Indiana.

"Western bean cutworm has been steadily moving east from Nebraska in recent years," Krupke says. "In the last several years it spread from Nebraska to Iowa, where some of the highest populations have been found.

"Last year the pest was found in Illinois. We started trapping the moths in Indiana this year, as well as Wisconsin, Michigan and Ohio. We found moths in all of those states. The highest concentrations of western bean cutworm moths we've found in Indiana are in northwest parts of the state, closest to the sites of infestation in Illinois. We've also found moths in eastern counties, such as Randolph and Whitley. It is important to note, however, that the moth numbers are not very high and we haven't documented any damage by the pest yet in Indiana."

There are insecticide treatments and at least one Bt corn variety
effective in controlling the pest, Krupke says. Because moth numbers are low he doesn’t recommend growers treat their fields at this time.

"We would recommend growers scout their fields for this pest," he says. "Scouting methods are like those for corn earworm. Start in July and look at plant leaves for eggs. Also look for larval feeding."

Western bean cutworm moths are dark brown with a white stripe on their upper wings and measure about 3/4 in. long. Larvae are about 1/4 in. long when hatched and can grow to a length of 1.5 in. Young larvae are tan and become a pale brown as they develop. Older larvae have three light stripes on the back of their heads.

"There's one generation of western bean cutworm each year," Krupke says. "Adult moths emerge in early July, move into cornfields and lay 20-50 eggs on the upper surface of corn leaves. The eggs hatch and the larvae will feed in the whorl for the early part of their life cycles. Once the tassel emerges they'll feed on the tassels. They'll eventually move into the ear and silks, where they will conclude their feeding for the season.

"In the worst-case scenarios, you may see a 4-bu./acre yield loss, which is significant. But even in places like Iowa where the pest is more prevalent, the western bean cutworm isn't a key pest – it's more of a hotspot sort of insect, with some damage in some fields. You don't tend to see a 50-acre field entirely wiped out by this pest."

WBC overwinters as late-stage larvae in fields, Krupke says.

Growers who suspect their fields contain WBC larvae are encouraged to report possible infestation to Krupke at (765) 494-4912 or by e-mail at [email protected]; or contact their county office of Purdue Extension.

"Producers also can take a digital photo of a living larva and e-mail it to us, or send us a larva that they've found," Krupke says.

For more information on crop pests, visit Purdue's field crops
integrated pest management Web site at
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