Japanese beetle outbreaks have been reported in many areas recently. This insect attacks more than 300 species of plants and is one of the most destructive of all garden pests when present in large numbers.
The beetles tent to feed in groups, eating the tissue between veins of the leaves so that only a skeleton of the leaf remains. They are particularly fond of roses and the only way to save the blooms is to cut them when they start to show color and take them indoors.
There is no mistaking the beetles. They are about 1/2-inch long and have metallic green bodies with bronze wing covers.
The beetles start to emerge from the ground in late June and early July. They usually reach their peak of abundance in late July and early August, and then begin to subside until they disappear altogether in late September.
Each female lays 40 to 60 eggs in the ground, a few at a time. These eggs hatch into larvae commonly called grub worms. The grubs feed on the roots of lawn and pasture grasses. A heavy infestation can do serious damage to a lawn: all the roots may be devoured and the grass can be rolled up like a rug.
For control of Japanese beetles, specialists recommend two steps: Spray with Sevin to protect the plants the beetles are feeding on: apply Milky Spore Disease powder to the lawn to destroy the grubs that hatch.
Sevin usually provides about a week's protection, but there are two disadvantages to its use. It destroys beneficial insects that help control harmful insects in the garden, and unless spraying is done in late afternoon, bees (so essential for pollination) also may be killed.
Beetles are good fliers, they've been found up to five miles out to sea, and this makes it tough to protect plants during the growing season. The presticide kills the beetles but more fly in to feed on the tender new growth.
If you have only a few small plants being attacked by the beetles, you can collect the beetles by hand (they can't sting or bite you), dropping them into a jar of water and detergent.
Milky Spore Disease powder (available at large garden centers and environmentally safe) contains a bacteria organism that causes the grub to become disease.
It may take a year or two before the full effect can be seen, but when grubs succumb to the disease, billions of bacteria spores are liberated in the soil. Such spores remain viable for years ready to infect and kill subsequent generations of grubs before they can do serious damage.
Laboratory investigations have indicated that in a few places the milky disease powder became less effective after 15 to 20 years.
Biological control of the beetle may be possible sometime in the future. USDA scientists have isolated, identified and systhesized the beetle's sex attractant, a lactone produced by the female beetle.
Traps baited with the systhesized attractant captured more males than traps baited with live virgin females in field tests in North California.
Another natural enemy of the Japanese beetle, a nine-inch nematode, has been identified, that parasitizes the beetle grub. It has been found in Vermont and at golf courses in Schenectady, Beacon and Sarasota Springs, N.Y. A species similar to the one found in Vermont is known to infect May and June beetle grubs in Russia.