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Start scouting for western bean cutworm

Purdue University entomologists predict western bean cutworm to peak in egg laying over the next couple of weeks.

The insect is relatively new to Indiana and Ohio, said Christian Krupke. The pest originates in the Great Plains states, but has been increasing in the region since 2006. So far, 2010 looks to be the worst year for infestation.

The pearl-like eggs are found in clusters of 50 to 100 and turn deep purple before hatching. Once hatched, larvae quickly enter into the corn whorl and eat until ears form. Molds often form where worms have eaten.

Krupke expects the northwest corner of the state to experience greater populations of western bean cutworm because the soils are sandy, making it easier for the insect to dig into the soils to overwinter.

“We know eggs are present in many fields in northwestern Indiana,” he said. “There will be many more deposited over the next couple of weeks, so scouting is essential in high-risk areas of the state.”

Although some Bt hybrids offer control, insecticide sprays are effective if applied at the appropriate time. This includes field monitoring to find eggs. It is important to scout for western bean cutworm now, because in two weeks it will likely be too late.

“When scouting, farmers need to be sure to look for egg masses,” Krupke said. “Treating newly-emerged larvae with insecticides is effective if the insecticides contact larvae on their way out of the eggs and into the plant. By the time they are adults, it becomes too late to treat them.”

Egg masses are generally laid on the top surface of the plant’s newest, or uppermost leaves.

If more than 5% of the plants in a field are infected, Krupke advises treating with insecticide.

“Early insecticide applications are better than late ones,” Krupke said. “Pyrethroid insecticides will offer enough residual activity, in most cases, for several days. These residues will kill hatching larvae as they travel on their way into the plant’s whorl or leaf axils.”

Once they get inside the whorl, or ear, of the plant, western bean cutworm cannot be controlled with insecticides.

To read more about western bean cutworm visit http://extension.entm.purdue.edu/pestcrop/2010/issue14/index.html#western . To watch Krupke demonstrate correct scouting techniques visit http://extension.entm.purdue.edu/pestcrop/2010/issue15/index.html#cutworm .

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