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White Grubs

September 1, 1999

So far, we have not received any reports of high white grub numbers or heavy damage. Conditions were right in early July for egg laying to be concentrated in irrigated turf, and the flights of both Japanese beetle and masked chafer adults were large. Typically, white grub damage makes itself known by late August, particularly in the southern and central areas of the state.

Keep a watch on irrigated areas that you havenít treated. Brownish turf areas that are 6 inches to a foot across can be an early sign of a grub damage problem that is about to explode into major damage. Realize that this early damage mimics some turf disease symptoms. Pull up the turf in these areas to check for grubs. Ten or more C-shaped white grubs per square foot should be in the root zone, but they may be deeper if the soil is dry. At this time of year, the grubs should be about 3/4 inch long. Turf damaged by white grubs is also easily pulled up because the roots have been eaten. Unlike root-diseased turf, the sod holds together and comes up like a carpet.

Rescue grub treatments include trichlorfon (Dylox, Proxol) and bendiocarb (Turcam). Both of these insecticides should kill the grubs in three to five days, giving immediate relief. Diazinon also quickly stops grub damage, but the treated, nonfeeding grubs live for about three weeks before dying, which is difficult to explain to clients. Remember that diazinon cannot be used on sod farms or golf courses. Hb (Heteror habditis bacteriophora) nematodes are also effective once the grubs are present. Water in any application with at least 1/2 inch of water to get the insecticide or nematodes down into the root zone where the grubs are located. If the soil is dry, water a couple of days before treating to entice the white grubs up into the root zone where they can be more effectively controlled.

Consistent watering at this time of year and in the spring can replace an insecticide application if grub numbers are moderate--in the range of 10 to 18 grubs per square foot. If you provide plenty of water, the turf will grow new roots as fast as the grubs eat them, as long as there arenít too many grubs. Remember that raccoons, skunks, and birds may damage turf while feeding on as few as three grubs per square foot, so there are situations when treatment is warranted where there are few grubs.

Author: Phil Nixon


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