Adult beetles are usually out for about six weeks, which means most should be gone by mid-August. After mating, beetles lay their eggs in the soil. Eggs hatch into grubs that may feed on various plant or turfgrass roots. Thus it is possible for lawns to be damaged later this summer by the grubs. Japanese beetles overwinter as grubs in the soil, and emerge as adults again next June to start the cycle over again.

Actively feeding beetles can be controlled using carbaryl (Sevin). Repeat the application at about weekly intervals. Treatment is generally suggested for smaller plants, or perhaps those near entrances or other key landscape locations. Treating large trees is rarely suggested. Also, research has shown Japanese beetle traps to be ineffective, and may actually draw more beetles into the area.

Automatically treating lawns in areas where the beetles currently are feeding is not suggested. Only treat lawns for grubs if in fact grubs become a problem in the lawn. You may see adult beetles now on trees and shrubs but no lawn damage from grubs later this summer. And even if you were to kill all the grubs in the soil, there is no guarantee more beetles still don't appear next season on your trees and shrubs, as they fly in from other areas.