The adult Japanese beetle attacks shrubs and vegetables and is a common garden pest. Its larvae also wreaks havoc in soil. When present in your lawn in sufficient numbers, the beetle grubs can quickly stress the grass and destroy the lush appearance of your yard. Determine whether you have grubs in your lawn and treat your yard with insecticides if necessary to defend your landscape's health and beauty.
Review the appearance of your lawn. Grubs attack the grasses' roots and reach the peak of their activity in late summer. Symptoms include random wilting and irregularly shaped brown spots.
Check the soil if you notice irregularly shaped brown spots or wilting. Insert a spade into your lawn turf and pull back the grass to see the soil at the root level. You'll see the grubs if your lawn is afflicted with them. The grubs are white, from 1/16 to 1 1/4 inches long and curl into a C shape when exposed.
Measure the infestation. Many lawns have grubs, but treatment is necessary only if the grub population swells out of control. Map out a 1-square-foot plot in your lawn and pull back the grass within that area. Lawns need to be treated only if 10 or more grubs are found in that space.
Spray your grass with grub-targeting insecticide if your lawn has a large amount of grubs. Standard lawn insecticides used to treat grubs include permethrin, carbaryl and acephate. Apply the insecticide according to its labeled guidelines because toxicity varies by product.