Purdue Extension, Dubois County – With the return of summer also comes the return of the most devastating pest of garden and landscaping plants in the United States – the Japanese beetle. The eastern US provides a favorable climate, hundreds of edible plant species, and no effective natural enemies for these jeweled pests of lawns, fruits, and landscaping.
The adult Japanese beetle is shiny metallic green with bronze-colored wing covers, and has six tufts of white hair along each side of its abdomen. An adult is about ½ inch long, and the young larva is a large, white grub about ½ to 1 inch long.
The life cycle begins with an egg laid in the soil in July or August. The larvae hatch and feed on decaying vegetation and grass roots. The grubs overwinter deep in the soil, pupate in early summer, and emerge from the grounds as adults in late June or early July.
Adults will eat over 300 species of plants, devouring leaves, flowers, and overripe or wounded fruit. Working as groups, the beetles will usually begin feeding at the top of a plant and work downward. They are most active on warm, sunny days, and prefer plants in direct sunlight. A single beetle does not eat much; it is the group feeding of large numbers of beetles that causes the noticeable damage. When attempting to control Japanese beetles, it is important to recognize that even if you are able to control both grubs and adults from your own property, the adults’ ability to easily fly large distances will allow others to come in from neighboring properties.
Plant selection around the home can greatly influence beetle activity, and choosing species not favored by the beetles when establishing new landscape plantings can help reduce beetle numbers. Preferred species of plants include roses, grapes, lindens, sassafras, Norway maple, Japanese maple, purple-leaf plum, many crabapples, and others, as well as weeds such as elder, multiflora rose, velvetleaf, poison ivy, smartweed, and wild grape. Plants seldom damaged include flowering dogwood, red and silver maple, ash, tuliptree, sweetgum, hickory, most native oaks, and ash.
For small plantings or small infestations of beetles, removing beetles by hand may control the problem. Odors from beetles on a plant will attract more beetles, causing further damage. An easy way to remove Japanese beetles is to shake them off early in the morning when they are sluggish, using a bucket of warm, soapy water to catch and destroy them. Exclusion from plants such as roses can also be done using cheesecloth or netting.
Chemical controls when numbers are too large to handle by hand removal include several homeowner insecticides, including carbaryl (Sevin) and pyrethroid products such as cyfluthrin (Tempo, Bayer Advanced Lawn & Garden Multi-Insect Killer), bifenthrin (Onyx, TalstarOne, deltamethrin (Deltagard), lambda cyhalothrin (Scimitar, Spectracide Triazicide), esfenvalerate (Ortho Bug-B-Gon Garden & Landscape Insect Killer), and permethrin (Spectracide Bug Stop Multi-Purpose Insect Control Concentrate). Carbaryl provides 1 – 2 weeks of plant protection, while the pyrethroid products provide about 2 – 3 weeks of protection from beetles. Botanical alternatives include Neem or Pyola, and provide 3 – 4 days of safety for plants.
Japanese beetle traps are a frequently used, but very ineffective, control for beetle damage. There are two types of scents used in these traps – one which mimics the male and female scents of beetles to attract the insects, and the other which is a sweet-smelling food based lure that attracts all beetles. The combined scents can attract thousands of Japanese beetles a day, but research shows that they rarely catch most of the beetles attracted, resulting in susceptible plants along the flight path sustaining much more damage than where the traps are not used. If you decide traps will be part of your beetle management plan, make sure the traps are placed on property borders far from susceptible plants (i.e. do not place in the middle of your garden, which will attract larger numbers to your plants).
For additional information on Japanese beetle control, check out the free Purdue publication “Japanese Beetles in the Urban Landscape” (E-75) at https://extension.entm.purdue.edu/publications/E-75.pdf .
If you would like more information, please contact Purdue Extension – Dubois County at 812-482-1782 or kjeck@purdue.edu.
