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Corn rootworm numbers dwindling

Jeff Caldwell 08/11/2010 @ 8:37am Multimedia Editor for Agriculture.com and Successful Farming magazine.

Corn rootworm numbers are at their generally lowest levels in years in the Corn Belt, according to new information from Purdue University entomologists.

Blame the wet spring and summer, as well as new Bt corn hybrids, for the lower rootworm pressure, says Purdue entomologist Christian Krupke. Saturated soils in the spring, when rootworm eggs are usually hatching, has resulted in lower adult populations this summer. But, more importantly, the fact that more farmers are using Bt varieties has helped stem potential pesticide resistance when the production system is employed prudently, including recommended refuge acres.

"This particular pest has become resistant to many pesticides and crop rotation, so there's every reason to expect they could become resistant to Bt hybrids if given the chance," Krupke says in a university report. "The purpose of the refuge is to provide an area where susceptible pests can build up and, therefore, dilute any of those resistance genes."

That's not to say it's time to lay off on vigilance when it comes to rootworms. Though he expects fewer beetles to lay fewer eggs that will pressure next year's crops, we're entering into a critical time to gauge your specific rootworm potential.

"Now is the time when beetle populations can be assessed in pollinating corn and soybean for next year's rootworm risk where corn will be planted. Pollen from a multitude of weeds (e.g., foxtails, volunteer corn, ragweeds, lambsquarters, pigweeds, etc) will draw them in to feed, potentially leading to unexpected lodging," Krupke says. "Investigations in these areas during the next few weeks will help make informed control decisions for next year."

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