AMES, Iowa – This summer, Japanese beetles have made their presence known in many parts of Iowa, emerging in mid-June to eat the foliage, fruits and flowers of many different types of plants. It's common to find a horde of a dozen or more beetles at a time. That’s concerning, but how can foliage be protected?
Iowa State University Extension and Outreach horticulturists can help answer questions about how to best handle Japanese beetles.
Japanese beetles are defoliating my linden tree. Will they kill it?
Japanese beetles feed on the foliage, flowers and fruit of more than 300 different plants. However, lindens are one of their favorites. Defoliation of well established, healthy lindens (and other trees) is usually not fatal. Defoliation is most harmful to recently planted trees (those planted in the last two or three years) and trees in poor health.
Small, recently planted trees can be protected by spraying the trees with carbaryl (Sevin) or permethrin (Eight). Because of the short residual effect of the insecticides, repeated spray applications will be necessary. Also, be sure to water small trees on a regular basis during dry periods. Defoliation and drought stress may be too much for young trees to endure.
Can Japanese beetles be effectively controlled by using traps?
No. Research conducted in Kentucky and elsewhere found the traps do not effectively control Japanese beetles. Traps attract more beetles than they catch and may actually result in a larger population in the yard than would otherwise occur.
Will applying an insecticide to the lawn reduce the Japanese beetle population in my yard next year?
No. Controlling the Japanese beetle larvae (grubs) in the lawn in late summer will not reduce the number of Japanese beetles in the yard the following year. Japanese beetles are capable flyers and will migrate into the yard from nearby areas.
How long do Japanese beetles feed on plants in the yard and garden?
Japanese beetles are present for about six to eight weeks every summer. Adult beetles usually begin to emerge from the ground in late June and new adults continue to appear through July. Each beetle lives from 30 to 45 days. Most Japanese beetles are gone by mid- to late August.