I recently asked the Grape Guy from My Grape Vine Blog about the Japanese beetle problem I had on my grape vines and this was his response…
Adult Japanese Beetle
The Japanese beetle (Popillia japonica, also known as the jitterbug) is one of the most visible and most destructive feeders of grape vine foliage out there.
The Japanese beetle attacks most green parts of the grape vine, but mostly feeds on young leaves in the upper part of the canopy. Occasionally, they will feed on fruit also, making it unusable for export or table grapes.
When Japanese beetles feed on the leaves of the grape vine, they will eat the foliage surface material between the veins, leaving only the veins in place, which will look like they were skeletonized. Although mature, vigorous growing grape vines can tolerate quite a bit of defoliation, this insect can cause some serious damage to a grape crop.
The life cycle of the Japanese beetle:
Japanese beetles overwinter as larvae in the soil. They will feed on the roots of grass and other plant material. Adult beetles will become visible in late spring and may be present in vineyards until mid in summer. The adult Japanese beetle (as seen in the picture), has a distinctive, shiny green body and head, with copper-coloured wings. The sides and back of the body is covered with small white hair. The female Japanese beetle is bigger than the male and is approximately ½ inch long.
After mating, the female Japanese beetle will temporarily leave the grape vine, to lay up to sixty eggs in the soil of your vineyard or if you have a backyard vineyard, in your lawn. In midsummer, the eggs will hatch and will reveal small, white grubs or larva, where they will feed and hide up to 8 inches deep into the soil, to wait out the cold of winter.
Japanese beetle control:
Strange enough, in Japan
, where the Japanese beetle originally comes from, this insect is not a big problem! Why? The answer is; natural enemies that feed on the grubs.
For the organic grape grower, you can control Japanese beetle by putting out traps with a pheromone that attracts the female and a floral lure, that will attract the male. The disadvantage of using these traps are that you can lure more Japanese beetles to your vineyard, as they can fly quite long distances in a short amount of time.
A program with physical and biological control of the grabs is a more effective method of controlling Japanese beetle. The two nematodes that are most effective against Japanese beetle grubs are Steinernema glaseri and Heterorhabditis bacteriophora. Both these nematodes are commercially available.
Milky Spore (Bacillus popilliae), a naturally occurring host specific bacterium, will also attack the destructive white grubs.