Issue 15, September 23, 2014

White Grubs

White grub infestations continue to be widespread and scattered this year. There appears to be more mammal and bird damage than direct grub damage appearing. With the low number of Japanese beetle and masked chafer adults in most areas of the state, this makes sense. It takes ten to twelve grubs per square foot to cause turf injury. Even marginally high grub numbers will not produce obvious damage due to the periodic rains in most areas of the state. With sufficient rainfall and low grub numbers, the turf will grow new roots to replace those that are eaten by grubs.

Turf damage from skunk feeding on white grubs.

Turf damage from birds feeding on white grubs.

Mammals and birds commonly damage turf with as few as three grubs per foot square. While searching for and feeding on grubs, a single skunk in one night can make about 100 holes through the turf that are 2 to 3 inches in diameter. Raccoons peel back the sod in areas that are usually 4 to 8 inches wide to expose the grubs. Armadillos dig holes several inches deep and several inches wide to feed on grubs. Armadillos entered Illinois several years ago and are most common in the southern third of the state. However, several have been found in the rest of the state, including northeastern Illinois. Insectivorous birds, such as starlings, blackbirds, cowbirds, and robins, peck holes through the thatch to feed on grubs. Areas that have been heavily worked by birds look brown from hundreds of tiny divots of thatch having been pulled up. Where the grubs are numerous, robins in particular chicken-scratch, scratching away the turf in patches that are several inches across in searching for grubs. (Phil Nixon)

Phil Nixon

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