Issue 17, September 24, 2010

White Grubs and May Beetles

White grubs are still susceptible to treatment until the soil temperature in the turf root zone drops below 60 degrees F. That is the temperature at which Japanese beetle grubs descend deeper into the soil for the winter. Masked chafer grubs descend in the soil when the root zone temperature drops below 50 degrees F. Once they tunnel deeper, white grubs are usually below the level where sufficient insecticide will be present to provide control. To obtain quick control, trichlorfon (Dylox) is usually the insecticide of choice, typically providing control in 3 days.

True white grub adults (Photo courtesy Ron Hines, Growmark).

Fall tree planting and other digging activity commonly exposes May beetles, the adult stage of true white grubs, also called 3-year white grubs. Adults of the most common species emerge underground in late summer and early fall, remaining below ground until the following spring. They are stocky, one-inch long beetles, and either chocolate brown or reddish-brown. These adult beetles are unlikely to cause serious feeding damage, so control efforts are not warranted.--Phil Nixon

Phil Nixon

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