With no natural enemies in their environment, Japanese beetles are among the most devastating of all landscape pests in the United States. They attack hundreds of different kinds of plants, including trees, shrubs, turf grass, and vegetable crops.
Each beetle doesn’t eat very much, but they feed in groups, starting at the tops of plants and working their way down. They feed most actively on warm, sunny days, preferring plants that are in direct sunlight.
Japanese Beetle Description and Life Cycle
Adult Japanese beetles are about one-half inch long. They are metallic green with copper-brown wing covers and white tufts under the wing covers. The adults emerge from the ground in June and feed for four to six weeks, after which they die.
In addition to feeding, the adults also begin to mate soon after they emerge in the spring. The females lay their eggs in the ground, 40 to 60 eggs per female. The inch-long grubs that come out of the eggs eat the roots of turf grass and plants, and then overwinter in the ground.
The next spring they emerge from the ground as adults, and begin the cycle of feeding and mating over again.
Integrated Pest Management
Recognizing that Japanese beetles are here to stay, the U.S. Department of Agriculture (USDA) has developed a multi-faceted approach to controlling them that involves a variety of methods. Called integrated pest management, or IPM, this approach involves:
·Assessment. Before taking measures to control Japanese beetles homeowners need to survey their properties to determine the extent and location of any infestation. Garden centers sell traps for this purpose.
·Biological controls. Biological methods of controlling Japanese beetles use parasites, nematodes, and fungi to minimize infestations. While they take longer than chemicals to control the beetles, their effect lasts longer and does less harm to the environment.
·Chemical controls. Targeted use of pesticides can be part of an integrated approach to controlling Japanese beetles. All pesticides pose hazards to people, wildlife, and the environment, so homeowners must read and follow instructions carefully if they decide to use chemicals.
·Plant Selection. Adult Japanese beetles feed on a wide of range plants. Plants that are especially prone to beetle damage include apples and crabapples, grapes, roses, plums, and Japanese and Norway maples. One way to avoid problems with Japanese beetles is to grow plants that the beetles do not attack. If you want to plant a maple tree, for example, choose red or silver maple rather than the Japanese or Norway maples.
Instead of apples, grow pears or persimmons.
·Mechanical traps. Homeowners can set up traps that use lures to attract and capture Japanese beetles. Traps should be put out when the adult beetles emerge, usually between early June and late August. Local extension offices know the right time to place the traps in your area.
Want to Learn More About Japanese Beetles
The more you know about Japanese beetles the better you will be able to control them in your garden.
Clean Air Gardening sells an Excellent Organic Japanese Beetle Killer.
The USDA describes the IPM approach to Japanese beetle control in depth, including a detailed list of susceptible and resistant plants, in Managing the Japanese Beetle: A Homeowner’s Handbook.
Because infestations and control measures vary by location it’s important to consult your local extension office for current guidance for your area. Following are a few of the many factsheets provided by extension services around the country.
The University of Kentucky has great info related to Japanese Beetles in the Urban Landscape.
Here’s great tips on Control of Japanese Beetle Adults and Grubs in Home Lawns from the University of Ohio.
The University of Wisconsin can tell you all about the Japanese Beetle.