Japanese beetle a pest for all seasons

August 09, 2005|by Lori Young

What is the pest of the summer? The Japanese beetle has been the most-called-about insect from those in the county.

The adults feed on more that 275 species of plants and the grubs feed on turf grass. This has caused many problems for homeowners in the county, starting last fall with grub damage and continuing this summer with adult beetle damage.

The adult beetles defoliate leaves on many species of plants, liking those in the rose family best. Grubs eat the roots of turf grasses such as Kentucky bluegrass, fine fescues and ryegrasses, causing the grass to die. If you suspect grub damage, try pulling the grass up. The grass can be pulled up like a mat if you have a grub problem.

How to control the Japanese beetle requires knowing the life cycle.

The life cycle of the Japanese beetle is one year. The beetles emerge from the soil in late June. They then feed on leaves and flower petals and mate. They skeletonize the leaf so that is looks lacelike. They return to lay eggs in the soil in August. Most beetles lay eggs close to where they feed. So, if you had high Japanese beetle populations, be on the lookout for grubs this fall!


The eggs hatch in about 10 days and begin feeding on grass roots. This will cause brown spots to appear in the lawn. They will feed until about mid-October, when the grubs will move down 6 to 18 inches into the soil. In late March, the grubs return to the surface and feed on the roots again. By late May, they pupate and emerge as adults in June, starting the cycle again.

How do you break the cycle and get control? The cycle is easier to break in the grub stage, when the grubs are young. A product called Imidacloprid, which is found in commercial lawn care products that advertise season-long grub control, can be applied to your lawn from May through early July. If you did not apply a product with Imidacloprid, then you can use a product with Dylox in it. Check your lawn now for grubs. If you have more than 6-8 grubs per square foot, then chemical control should be applied. You can also protect your lawn by planting tall fescue, as it is grub-resistant.

Now, what about those adults? They have done most of the damage they are going to do this year. The control for the adults is to handpick them off and then drop into soapy water or spray with an insecticidal soap/pyrethrin blend. There is also a soil drench containing Imidacloprid that is labeled for adult Japanese beetles feeding on trees and shrubs.

I have also been asked about Japanese beetle traps. These traps are baited with an attractant that lures the beetle into the bag and then won't let it out. These traps will attract beetles from a large area and limit the damage to a small area. In other words, you can attract your neighbor's Japanese beetles to your yard and you see the damage. Research has demonstrated a 31- to 40-percent increase in plant damage when traps are used close to plants that the beetles like. Some of these plants are roses, willows, lindens, elm, grapes, Japanese and Norway maple, birches, pin oak, rose of Sharon, ornamental apples, plums and cherries.

Will Japanese beetles be bad next year? That depends on how many grubs are killed and the harshness of the winter, among other things. If you had Japanese beetle problems this summer, be on the lookout for grub damage this fall.

All information for this article was taken from Maryland Cooperative Extension publication HG 78: "The Japanese Beetle and Garden Insects of North America," by Whitney Cranshaw. If you would like a copy of Fact Sheet HG 78, check out this Web site,, or call me at 301-791-1604.

Lori Young is an Extension educator, specializing in horticulture for the University of Maryland Cooperative Extension. She is based in Washington County. She can be reached weekdays by telephone at 301-791-1604, ext. 14, or by e-mail at

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