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White Grubs

August 4, 2004

White grub eggs should be hatching toward the end of July in southern Illinois and in early August in central and northern Illinois. Both the northern and southern masked chafer (annual white grubs) and Japanese beetle eggs should hatch in these periods. With rainfall being plentiful during the first two weeks of July, coupled with relatively cooler conditions during that time through most of Illinois, white grub injury should be relatively slight this year.

When nonirrigated turf is attractive to egg-laying beetles because it is green and moist, eggs are typically laid in both nonirrigated and watered turf. This results in low numbers of grubs per square foot, resulting in little or no turf dieback due to root feeding. The dry weather in northwestern Illinois should cause grub damage to be heavy in that area. Throughout the rest of the state, grub injury will probably be limited to hot spots here and there. Be watchful for signs of turf wilting and dieback, check for grubs, and treat with trichlorfon (Dylox) if grubs are numerous.

Scout for grubs by cutting through the turf with a heavy knife and then pulling up the turf. The C-shaped, white grubs should be in or just below the turf’s root zone. If the soil is dry, the grubs may be 2 to 4 inches deeper. Check for these deeper grubs by tilling up the soil with the knife. Ten to 12 or more grubs per square foot usually cause obvious turf injury. Eight to 10 grubs per square foot may cause injury in heavily used turf, such as sports fields. Skunks, raccoons, and insectivorous birds may damage turf while feeding on as few a two to three grubs per square foot.

Author: Phil Nixon


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