Japanese beetles present a double whammy. The coppery-colored, half-inch-long adult beetles have been attacking plants. Eventually, their grub offspring will attack turf.

In sunny, moist areas, beetle grubs will hatch and feed on the roots of Kentucky bluegrass. They leave telltale dead spots.

"Peel back the turf, which should be easy to do. ... If you see 12 or more grubs per square foot, it's time to do something," says Donna Danielson with the Plant Clinic at The Morton Arboretum in Chicago.

To control grubs, you have several options. Keep your lawn healthy and watered in August and September.

Spray one application of nematode (microscopic roundworms) spray. For fewer than five or six grubs per square foot, apply the bacteria Bacillus popilliae. Annual applications for three or four years will build up levels high enough to control more severe infestations. Or, apply one chemical insecticide application. All methods must be watered in well.

They prefer roses, but they munch on the flowers or leaves of 300 other species of plants, including birch, linden and crabapple trees.

"When they find a good food source, they send a chemical signal to their friends, and then you get a bazillion of them," says Danielson.

If the adults are still in your yard, you can try hand-picking them off into a container of soapy water. If that doesn't work, apply a Neem oil-based spray to the plant, which makes it unpalatable. As a last resort, use an insecticide. Check your local Cooperative Extension Service for recommended treatments. Never use Japanese beetle traps, which attract more beetles than they kill.