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White Grubs

November 24, 2004

An overview of the white grub situation in Illinois shows that, in general, white grubs were not a major problem in turf this year. Most of the white grub populations that were large enough to be damaging were spotty, with an occasional turf area having severe damage. In general, the northwestern portion of the state from Peoria through Monmouth, Galesburg, and the Quad Cities had more white grub problems than other areas of the state. Fairly large areas of white grub infestations were also noted in Will, Kankakee, and southern Cook counties. Usually, at least 10 to 12 grubs per square foot are necessary to cause turf injury.

In many areas, the grub population was low, but treatment was still needed to control damage caused by raccoons, skunks, and birds feeding on the grubs. Raccoons peel up 4- to 8-inch pieces of turf to feed on the grubs in the root zone. Skunks usually dig up the sod in 3-inch-diameter holes, with a single skunk making about 100 of these holes in one night. Insectivorous birds, such as starlings, cowbirds, grackles, robins, and cuckoos, work their beaks through the sod searching for individual grubs. When they remove their beak and grub, they typically tear out a 1/2- to 1-inch-diameter divot. Hundreds of these small, brown divots in a small area are very obvious. Where the turf is thin and the grubs are near the surface, robins, in particular, chicken-scratch larger areas through the turf. These animals typically go after relatively small grub numbers in the range of three or more grubs per square foot.

White grubs can still be treated as long as they remain in the root zone. Once the temperature in this zone drops below 60 degrees F, Japanese beetle grubs tunnel deeper into the soil. Annual white grubs (also known as southern and northern masked chafers) and true white grubs (also known as May beetles) tunnel deeper in the soil when the root zone temperature drops below 50?F. In most years, only southern Illinois has treatable grubs until Thanksgiving; but with the mild temperatures this fall, more northern areas may see grub damage, particularly in areas where fall rainfall has been slight.

Trichlorfon, sold as Dylox, is typically the insecticide of choice for late grub treatments, but imidacloprid (sold as Merit), halofenozide (sold as Mach 2), and Hb nematodes should also be effective at this time of year. Make sure that the grubs are in the root zone before treatment. If they have already descended deeper into the soil, treatment is unlikely to be effective.

Author: Phil Nixon


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