They're back! Yes, the Japanese beetle have completed metamorphosis and the adults are back to enjoy a smorgasbord of leafy tissue in the garden. Is there anything that can be done to reduce the population?
The Japanese beetle spends most of its life (10 months) underground as a small, white, c-shaped grub that feeds on the roots of grass. The larvae usually begin to pupate in May and the adults emerge from the ground in late June. The unusual weather this year has aided the adult in appearing a few weeks ahead of schedule. Expect the adult to be here through July when it will lay eggs in the soil.
Eggs require moisture to survive and hatch. If there is good news in a lack of rain it is that fewer insect eggs will survive the drought to hatch out and become larvae. The grubs that do hatch will feed on grass roots until the temperatures begin to drop in the fall. At that time they will move deeper into the soil to wait for spring.
If control is desired then imidacloprid can be applied to the ground to control newly hatched larvae. This can be found as a granular application in Bayer Advanced and GrubEx. To time the application correctly aim between June and mid-August. Mow the lawn before applying any chemical control to allow for better penetration of the chemical into the ground where grubs are feeding. Water the lawn immediately after application to move the chemical into the ground. This can be done with irrigation if rain is not in the forecast. Read the label before using the product.
Control of Japanese beetles may be hard to achieve if yours is the only yard applying chemical control. Adult beetles can fly in from other locations next season even if there are no grubs found in the soil in your garden. Traps will collect adult beetles but they will also attract them to the property so avoid using these for control.
Another approach to consider when facing off against the pest is to avoid plants that are most likely to be eaten by Japanese beetles. Following is a list of many of the beetles favorite foods: Japanese Maple, Norway Maple, Horsechestnut, Hollyhock, Gray Birch, American Chestnut, Rose-of-Sharon, Black Walnut, Flowering Crabapple or Apple, London Planetree, Lombardy Poplar, Cherry, Plum, Peach, Roses, Sassafras, American Mountain Ash, American Linden, American Elm, English Elm and Grape. If these plants represent some of your favorites then you may have to learn to live with the Japanese beetle found in the area.
Sources for this article: M.F. Potter, D.A. Potter, and L.H. Townsend. Japanese Beetles In The Urban Landscape. ENTFACT-451. University of Kentucky College of Agriculture. Department of Entomology. January 2006.;
The Extension office is open Monday - Friday, located in Kennett, Missouri at 101 South Main Street (the old bank) on the 2nd floor. For horticulture questions contact the horticulture specialist at 573-686-8064. MU is an equal opportunity/ADA institution.