These beetles are especially bothersome on roses and peonies. The adults feed in swarms, attacking flowering plants first, then going on to others. They eat holes in blossoms and chew leaves to lace. In their grub form, they infest lawns and damage grass roots much as Japanese beetles do; you'll find patches of lawn that are severed at the roots and can be rolled up like carpet. Rose chafers are particularly troublesome in sandy soils.
You may find both rose chafers and Japanese beetles on your roses at the same time, and controls for the two are similar. Handpick any adults you see; pyrethrin may also be used against them. To kill larvae, drench lawns with parasitic nematodes.
Chemical controls effective against adults include acephate and carbaryl. Diazinon can be used to kill larvae in lawns.