Damage caused by the adult feeding on leaves is easy to distinguish by the skeletal remains of leaves on plants. The adult feeds on all green tissue until only the veins are left behind. Adults emerge sometime in the first part of June in our area. Feeding continues until they lay new eggs in July. The larva of the Japanese beetle is a grub that hatches in the later part of the summer, increases in size within 40 days and overwinters in the ground just below the surface. Feeding is concentrated on the roots of turf grasses, usually those that are irrigated.
If populations are high enough, this feeding can cause damage to the health of turf. Control measures may be applied by using contact formulas during the adult stage of the insect but multiple applications will be needed as there will be more than one population that attacks each season. Control can also be hard to achieve if neighbors are not working toward the same goal. If you control those adults present in your yard, other adult beetles may move in once the competition is gone.
Control may also be applied to the larva, or grub stage just as you would control grubs that feed on turf grass. It would be better to concentrate on the larva before they pupate into the adult beetle stage as this would help reduce the population by reducing the number of adults that lay eggs in July. Larvae begin pupating by April and feed for 4 to 6 weeks prior. One word of caution, while Japanese beetle traps do attract and catch adult beetles, these traps attract more beetles than are actually caught in the traps. Consequently more damage will be caused to the immediate area than would have been caused without the trap.
One way of controlling attacks by the adult beetle is to avoid using their favorite plants in your landscape. Some of the more favorite plants include grape, roses, linden tree, prunus species, Norway and Japanese maples. Permethrin and pyrethroid are effective in controlling adult beetles as is carbaryl. Consider the health of bees in your landscape when you are deciding on a method of control.
You may do just as well by spraying insecticidal soaps on shrubs that are heavily infested with the adults. Granular applications of Merit may be used on turf to control the larvae stage of the Japanese beetle. Source: Japanese Beetles in the Urban Landscape. M.F. Potter, D.A. Potter and L.H. Townsend. University of Kentucky Cooperative Extension Service. Entfact-451. The University of Missouri Extension Center is located in Kennett, Missouri at 101 South Main Street (the old bank) on the 2nd floor. Open Monday - Friday. University of Missouri Extension programs are open to all.
Sarah Denkler is a horticulture specialist
with University of Missouri Extension
in Dunklin County.