HYG  Pest newsletter

Issue Index

Past Issues

Annual White Grubs

Although all indications are that larval annual white grubs should be present now in large numbers, we have yet to find any in central Illinois or in any other part of the state.

The adult beetles emerged later than usual, probably because of the cool spring. We normally first see adults in east central Illinois on the evenings of July 2 or 3, but we did not see them until July 7, almost one week later. July 18 was the last time that we saw beetles in central Illinois.

Because the beetles do not feed, they normally live for only about two weeks. At The Morton Arboretum in northeastern Illinois, annual white grub adult flight peaked on July 22, and a few were still present in the first week of August. In most years, annual white grub flight is over in northern Illinois near July 25. Beetle flights ranged from normal in some areas of the state to above average in many areas, including central Illinois.

When turf is dry and dormant, the adults migrate to irrigated turf to lay their eggs. Unirrigated turf throughout most of Illinois was dry and dormant in July. This should have resulted in large numbers of eggs being laid in watered turf.

The eggs that the masked chafers or annual white grub adults lay usually hatch in two to three weeks. High soil temperatures around 90°F and above will reduce hatching. However, soil temperatures have been in the 70s during this time. The resulting white, C-shaped grubs are easily noticed against dark soil, even the newly hatched ones, which are approximately 3/16 inch long. They are present in the root zone of turf if the soil is damp. Dry soil will cause the grubs to move downward in the soil column.

With the late flight of the beetles, we do not anticipate damage to occur until late August in southern Illinois and until almost mid-September in northern Illinois. Grub numbers of ten or more per square foot are likely to cause turf damage.

If raccoons, skunks, or birds feed in the area, turf damage will occur at much lower numbersthree to five grubs per square foot. Raccoons peel back four- to twelve-inch-wide sections of turf to feed on the grubs. Skunks tear out divots of turf that are three to six inches in diameter. While a raccoon usually tears out six or fewer sections of turf in an area, a skunk usually makes 30 or more holes. Birds pick at the turf, tearing out the sod in one-inch pieces. Such feeding causes the affected areas to turn brown from the removed thatch and sod.

If treatment for grubs is needed at this time, use faster-acting insecticides such as trichlorfon (Dylox, Proxol), bendiocarb (Turcam, Intercept), or isozofos. Triumph is labeled for use only on home lawns, sod farms, and golf course tees, greens, and aprons. Diazinon is not labeled for use on golf courses or sod farms. Grubs treated with diazinon will stop feeding but will take about three weeks to die.

Author: Phil Nixon Fredric Miller Karel Jacobs


College Links