All you need to know about the Japanese beetles in your garden
The metallic green head and copper-colored wingcovers make this beetle easy to recognize. It devours many members of the rose family, marigold, zinnia, and most vegetables. The small, grayish white grubs feed on roots and are especially troublesome in lawns. Japanese beetles are most common east of the Mississippi, but they have been found in Southern California.
Employ a variety of management techniques. Till the soil in the fall to expose grubs to birds. Keep floating row covers on vegetable crops. Handpick any adults you see. Drench lawns with parasitic nematodes or milky spore disease (a disease caused by Bacillus popilliae and B. lentimorbus); you may need to treat extensive areas, including neighboring lawns, for this to be effective. Pyrethrin may control adults.
Chemical controls include acephate and carbaryl (for adults) and diazinon (for grubs in lawns).