The Japanese beetle, Popillia japonica, is a scarab beetle about 3/8" long. The head and thorax are metallic green and the elytra (outer wing covers) are copper-colored. Adult feeding damage appears as lacey leaves. The Japanese beetle feeds on over 400 plants including rose, raspberry, bean, grape and blueberry. The adults are good fliers and can move from one area to another in large swarms. When threatened, adults will feign death, dropping from the plant.

The larval stage is a C-shaped white grub similar in appearance to the June beetle, rose chafer and European chafer. Japanese beetle grubs can be a major turf pest. A good indicator of a white grub infestation is skunks digging up the lawn. White grub treatment threshold is typically eight grubs per square foot.

Life Cycle

Japanese beetles usually emerge in the beginning of July and can be found right through September. After mating, the females lay eggs in turf. The eggs hatch and the young white grubs feed from early August until the first hard frosts of fall drive them deeper into the soil. After hibernating through the winter, the grubs migrate into the turf root zone to feed again in May and June. Around mid-June, the grubs pupate, eventually emerging as adults in early July.

Management

Managing adult Japanese beetles is challenging because of the large numbers that can occur throughout the summer. A combination of approaches is suggested. Although controversial, you may want to consider pheromone traps as part of your management strategy. Be sure to place traps at least 50 feet away from the plants you want to protect. Also, do not wait for the trap bags to completely fill before emptying. Poorly maintained traps can be a liability instead of a help. Protective barriers (e.g. spun-bonded material) can be used to protect susceptible plants during massive influxes of beetles. Handpicking can help if practical (may have to be done several times daily). Foliage can be protected with sprays of pyrethrins, rotenone, neem, methoxychlor, malathion, and carbaryl (Sevin). Repeat applications are often necessary for management of this pest.

Japanese beetle white grub management is best timed when the white grubs are small and feeding in the turf root zone (late summer into early fall). In New England, beneficial nematodes have been shown to be effective in managing white grubs whereas milky spore has had spotty results. Insecticides such as imidacloprid (Merit) or carbaryl (Sevin) are also an option to consider.  Targeting the grub stage in hope of relief from the adult beetle often leads to disappointment.