Japanese Beetle, Popillia japonica Newman   

Description and Life Cycle

The adult beetles feed on the foliage and fruits of more than 250 kinds of plants, but grape is one of the preferred hosts.  The larvae are C-shaped grubs found in the soil, and are serious pests of grass roots.  The adult beetle has a shiny, metallic-green head and thorax, and coppery-brown wing covers.  Tufts of white hairs are located along the sides of the body.  Adult beetles are about 1/2 inch long.

This insect overwinters as a larva below the soil surface.  Larvae feed principally on grass roots.  During late spring, larvae move closer to the soil surface and complete their development; adults emerge in late-June or early-July.  Eggs are laid in the thatch layer of soil and take 10 days to hatch.  There is one generation per year.

 

      Life cycle of the Japanese beetle in Ohio.

       Adult beetles emerge from the ground in June and July, and begin feeding upon foliage.  Mating occurs at this time and eggs are laid in the ground.  Eggs hatch in August and young grubs begin feeding on plant roots.  Grubs continue to feed and grow until cold weather, at which time they tunnel 3 to 12 inches down and make overwintering cells.  In the spring when soil begins to warm, grubs move toward the surface where additional feeding may occur before pupation in May.

Damage Symptoms

The adults feed on the leaves of both wild and cultivated grapevines.  Beetles prefer foliage exposed to direct sunlight and often are seen clustered together feeding on tender vegetative parts.  Vines with thin, smooth leaves, such as French hybrids, are preferred over those with thick, pubescent leaves, such as Concord.  Concord vineyards rarely need special control sprays for Japanese beetles.  On the other hand, French hybrids and other thin-leaved cultivars require frequent inspection to prevent damage.  Damaged leaves have a laced appearance, and severely affected leaves will drop prematurely.

Management

There is no economic threshold on the number of beetles or amount of damage that requires treatment.  If a susceptible cultivar is being grown and growers previously have experienced high populations of Japanese beetles, an insecticide should be applied when beetles emerge and thereafter as needed.

Monitoring

 Japanese beetle lure and trap is available for monitoring this pest, however these beetles are easily detected while walking through the vineyard and if skeletonizing of leaves becomes evident, thin leaved cultivars may need to be protected with an application of insecticide.  The usual threshold for making a spray application is about 15% of the leaves damaged. 

Control

Insecticide is usually applied when feeding is apparent on most vines and skeletonized leaves are found.  Spot treatment is adequate in some cases.  An insecticide with long residual activity is needed when beetle populations are high.  Repeated applications may be needed to control new beetles flying in from surrounding areas.

A microbial insecticide is available to control Japanese beetle grubs in turf, although it is slower acting and more expensive than conventional insecticides.  This substance is bacterial in nature and causes milky spore disease within the grub stage of development.  This microbial insecticide can not be relied upon to protect grapes from Japanese beetle. 

Current pesticide recommendations may be found Here