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Corn Rootworm Larvae and Rescue Treatments

June 28, 2002
At this point in the summer, reports of corn rootworm larvae are becoming more common. Howard Brown, manager of agronomy services, Growmark, detected two corn rootworm grubs per plant while troubleshooting a field of uneven corn near Armington (southeast corner of Tazewell County). The field had been planted to soybeans last season. In the coming weeks, following the emergence of western corn rootworm adults, it will make very good sense to monitor densities of this pest in soybean fields. We've discussed many times how Pherocon AM traps can be deployed in soybean fields to help producers monitor densities of western corn rootworm adults. In the upcoming issues of the Bulletin, we'll revisit this topic and review the scouting protocol and thresholds used with these traps.

In the past week, a few folks have called and asked about rescue treatments for corn rootworm larvae. In some cases, people were not satisfied with the performance of their soil insecticide or they neglected to use any product in the first place. Keep the following factors in mind when deciding whether or not to attempt a rescue treatment. Soon after July 4, the first "flush" of corn rootworm adults will begin to emerge. Although root injury will continue to occur through mid-July in many fields, decisions regarding attempted "rescues" should be made very soon. In many fields, the corn is already too tall for any attempt to limit larval injury with ground application equipment. For the most part, rescue treatments do not work very well for corn rootworms. Furadan 4F and Lorsban 4E are products labeled for use against corn rootworms at cultivation. Of the two products, Furadan 4F is more water soluble and may move into the root zone more readily than Lorsban 4E. The efficacy of both products would be enhanced with precipitation following a treatment. The key factor in limiting larval injury is for product penetration to occur into the root zone. If an infested field can be irrigated, control also is likely to be enhanced following the application of a rescue treatment. Finally, keep in mind that many corn hybrids are capable of regenerating root tissue, especially if soil moisture is not limiting.--Mike Gray

Author: Mike Gray

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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