Although we suffered through one of the worst droughts of the century last year, much of the damage to the turf in 1999 was caused by white grubs, the larval stage of the adult beetle.
Our area had five or six beetle types; two in particular cause problems.
We have always had the Japanese beetle. We now are seeing an infestation of European Chafer, starting in the northern suburbs. Entire neighborhoods in suburban Detroit have suffered lawn damage from these beetles and their grub offspring.
Lawn experts agree that to understand how to control these insects, one must understand their life cycle. The grub's metamorphosis to the beetle takes a year. The adult beetle mates in the summer and the female lays her eggs in the soil below the sod line. Generally, the eggs hatch in July or August and the emerging grub moves upward and begins feeding rapidly on grass roots. Its legs give it the mobility to do damage to large areas.
The growing grubs feed until frost permeates the soil. Then, they go below the frost line for winter. In spring, they come back to the root level for last meals before they pupate and change into adults to start the cycle again.
The reason damage is so prevalent in the fall is linked to rainfall and turf vigor. September, October, and November are among a year's driest months. If grubs have severely damaged the roots by the autumn, sod will roll up like a carpet. With no root structure, the grass cannot live.
In spring, when rainfall usually is more plentiful, even root-damaged turf usually can get enough moisture to survive. And grubs slow their eating as they head into the pupal stage that precedes adulthood.
In the past, grubs often were treated with strong pesticides such as Diazinon, Ofranol, and Dylox in hopes of curing the problems after the grubs were seen. Today, we have products that are much more environmentally friendly and approach the problem in a preventive manner. Two such products are Merit and Mach 2. These are not contact insecticides; rather they affect the grubs' appetite and growth habits.
These products affect the smallest grubs in August, and should be applied before grubs hatch, ideally between Memorial Day and August. Prior application could hinder the result, and after Aug. 1 the grub will be too big for control.
If you have grubs and did not apply a preventive treatment in the fall, a curative approach is your only alternative. Grub control in the spring is difficult because the grubs are large in readiness for pupation. Controls used this spring will not ensure eradication of new larvae in the fall.
If forecasters are correct in predicting another drought year, homeowners should think prevention in their approach to grub control. Low rainfall makes conditions difficult for grub-damaged grass to survive.
Mona Macksey is a free-lance writer for The Blade.
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