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Reports of White Grub Injury Still Trickling In

July 14, 2000
As odd as it seems, we are still receiving an occasional report of white grubs causing damage to crops. Recently we received a report of white grubs causing serious damage to soybeans in Scott County. The roots apparently showed signs of white grub feeding activity. I received specimens of the grubs and photographs of both the grubs and aboveground symptoms of injury from two separate sources. I examined the grubs under a microscope, and, although they appeared to be "true" white grubs (Phyllophaga species), something about them made them look a little different from the grubs we usually receive for identification. However, there are many species in the genus Phyllophaga, and identification to species usually is difficult.

Information about most Phyllophaga white grubs indicates that the grubs feed throughout the summer during their second year in the soil. Therefore, it's not unusual to find grubs in field crops during the summer. However, the presence of white grubs in a field does not necessarily mean that the grubs are responsible for the injury. Our crops in many areas of the state have suffered several stresses this summer, not the least of which is "wet feet" after continuous, heavy rainfalls. The excessive rain that has occurred in some areas has resulted in aboveground symptoms of injury that may resemble injury caused by other factors, including white grubs. So bring your diagnostic skills to bear whenever you visit fields that just don't look right. A mistake in diagnosis could result in unnecessary or misplaced concern.--Kevin Steffey

Author: Kevin Steffey

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

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