Japanese Beetle Management

June 26, 2007

Pheromone traps are available that contain a pheromone (externally produced hormonelike chemical) attractive to male Japanese beetles. They also contain a floral lure attractive to female beetles. Yellow vanes and funnel (the beetles are attracted to yellow) lead to a bag or other container to hold the trapped beetles. Research shows that beetles are attracted from a considerable distance to areas near the traps but then switch their seeking behavior to food plants, resulting in heavier plant damage near traps. Even though the traps catch large numbers of beetles, we do not recommend their use except in unusual situations.

Japanese beetle trap.

Netting is used to provide complete protection. Rosarians protect prize individual buds and blooms or even entire plants with netting. Backyard blueberry growers use netting as well. Shadecloth with a high light transmittance, spun-bound polyester row covers, netting sold in fabric stores, window screening, and other meshes all work well.

Insecticides provide effective control of adult Japanese beetles. Imidacloprid (Merit) moves systemically through the tree to provide control. Soil applications require 2 months to move through the tree and so are not practical now for this year’s infestation. Imidacloprid (Imicide, Pointer) injected into the trunk or root flare takes only 2 weeks to move through the tree. Occasionally, about one tree in seven, the imidacloprid does not provide control systemically, so you need to watch for this. Once in the tree, the imidacloprid should be effective for at least a year.

Carbaryl (Sevin), clothianidin (Arena), cyfluthrin (Tempo), and dinotefuran (Safari) provide about 2 weeks of protection per foliar spray. With the beetles present for about 6 weeks, three applications are typically required.

Because the adult beetles prefer foliage previously damaged by other Japanese beetles when they change hosts, early hand-removal of beetles is effective. In the late afternoon and evening, disturbed beetles fold their legs and drop to the ground. By holding a widemouth jar of rubbing alcohol (isopropyl alcohol) or soapy water under beetles and poking at them, one can easily collect a pint or so in less than an hour. If this is done every day or two for the first couple of weeks after the beetles emerge, subsequent damage through the summer is reduced. Although labor-intensive, this may be a viable option for clientele.