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White Grubs

October 16, 2007

There have been numerous reports of white grubs and associated damage in northeastern Illinois. Although there were heavy flights of Japanese beetles in both northern and southern Illinois, white grub damage appears to be spotty in southern Illinois. Japanese beetle eggs die at soil temperatures over 90F; and high temperatures coupled with very dry conditions in southern Illinois probably account for the lack of damage. Also, Japanese beetle grubs need 11 inches of rainfall or irrigation through the late summer and fall. Dry soils in southern Illinois have probably killed many of the resulting grubs that did hatch.

People in northeastern Illinois are questioning whether they have masked chafer grubs, annual white grubs, or than Japanese beetle grubs. Masked chafer grubs better survive the dry soil conditions that northeastern Illinois has experienced. However, masked chafers are typically reduced when Japanese beetle moves into an area.

I have not seen any grubs from northeastern Illinois. I will be happy to identify any that are sent to me. To preserve the grubs, drop them into boiling water, immediately fish them out, and put them into rubbing alcohol.

Regardless of the species, trichlorfon (Dylox) should provide control. If the soil is dry, irrigate 2 to 3 days before treatment to bring the grubs up into the root zone, where the insecticide can be effective. Water the Dylox in with at least 1/2 inch of water. The grubs can be effectively treated if they are in the root zone. Japanese beetle grubs migrate downward into the soil for the winter when the root zone temperature drops below 60F. Masked chafer grubs migrate downward when the root zone temperature drops below 50F.