Japanese beetles appear to be out in unusually large numbers in some areas this year. They attack nearly 300 different plants ranging from food crops and popular ornamentals to trees and even weeds. The beetles tend to feed in groups, eating the tissue between veins of the leaves so that only a skeleton of the leaf remains.
If they are chewing up your roses, you can blame Mother Nature. She provided the kind of weather it takes to trigger a population exploson of these pesky insects.
There is no mistaking the beetles. They are about 1/2-inch long and have metallic green bodies with bronze wing covers.
The beetle is the adult form of the insect. The pest spends about 10 months of the year in the ground as a white grub (this is the form that feeds on the roots of grasses) and begins to emerge mid-to-late June. They are at the peak of their abundance in July and the first part of August. Then they begin to decrease until they disappear altogether in late September.
Females alternately feed and burrow into the ground to lay eggs. Each female lays from 40 to 60 of them. These eggs hatch into larvae (commonly called grub worms) which feed on the roots of lawn and pasture grasses and sometimes on such plants as beans, tomatoes and strawberries.
If we could lure the beetles to feed on gerasiums, things might not be so bad. The geranium has a toxic substance that paralyzes and even kills some Japanese beetles.
Beetles are good flyers - they've been found up to 5 miles out to sea - and this makes it tough to protect plants from them. Pesticides kill the beetles but more fly in to take their place. Roses are especially hard to protect because the bloom unfolds too fast, offering attractive feeding of new growth which hasn't been exposed to insecticides.
Four insecticides are approved for use against Japanese beetle adults: Sevin, Malathion, Methexychlor and Diazinon. Directions on the label for mix and application should be followed closely.
Both Sevin and Malathion are highly toxic to honey bees and should not be used when the plants are in bloom. Also, they should be reserved for use during the late afternoon when the bees are not so active.
If you have only a few plants being attacked, you can collect the beetles by hand, dropping them into a jar or bucket of water and detergent. They cannot sting or bite or otherwise cause you personal injury. You'll have to do it every day when beetle activity is at its peak because more of the insects will be flying in.
Apparently diseased and poorly nourished plants are especially susceptible to attack, so proper fertilization, watering and healthy plants may go a long way toward insuring their survival of a Japanese beetle attack.