I have numerous spongy patches in the lawn, which I can easily tear out by...

Asked October 15, 2013, 1:03 PM EDT

I have numerous spongy patches in the lawn, which I can easily tear out by hand revealing an infestation of white grubs. What are they and how can I control them? The lawn is about 25 percent infested with these patches. (Coin in image is quarter)

Frederick County Maryland

3 Responses

The insects in your photo are the grubs (larvae) of scarab beetles. Some of the more common beetle grubs are those of Oriental beetles, Japanese beetles, and Asiatic beetles. These beetles lay their eggs in the soil under lush turfgrass in June and July. The eggs hatch in August and begin feeding on the grass roots. When there are large numbers of grubs, a dozen or more per square foot of turfgrass, the grass is destroyed. It is too late to control the grubs now. The grubs will be moving lower into the soil as temperatures drop. They will return to root level in April/May, but will quickly go into pupation and emerge as adult beetles in June. If we have weather conditions next year that are similar to this year, i.e., wet summer and lush lawns while the adult beetles are active in June, you may want to consider applying a grub control in July.

Can you suggest particular types of grub control? We had a outrageously large number of flying beetles over the lawn in the past June and July. They were not the familiar Japanese beetles, but were similar. Minor beetle damage to garden plants. I have heard of using Sevin and of Milky Spore Disease as control methods. Can you recommend using one of these or other measures? Thanks.

Milky spore disease affects only Japanese beetles. In order to control all species of beetle grubs that may be in your lawn, you should use a product containing imidacloprid (Trade name Merit). Typically, the available products are granular and in our area should be applied around the Fourth of July or shortly thereafter.
Sevin is not recommended for either adult beetles or for beetle grubs.