Japanese Beetles – They’re here…

Japanese Beetle

Japanese beetle on daisy

While they prefer roses, Japanese beetles will attack many plants, including daisies.

While several weeks later than last year, Japanese beetles definitely have arrived in Minnesota. I saw several on a garden tour last weekend and gardeners on the MSHS Facebook page chimed in that many have been seeing the beetles for at least a week. Jeff Hahn, one of the bug experts at the University of Minnesota Extension Service,wrote about them on July 10.

Here’s the 411 on Japanese beetles.

Food, Appearance, Lifecycle

Japanese beetles are most likely to begin their attack with roses, but once they get in a yard or garden, they will eat almost anything available, including geraniums, hollyhocks, Linden trees, beans, grapes, vines and fruit trees. Beyond roses, raspberries are a particular favorite. They typically feed in groups and it’s easy to spot them at the top of plants because of their iridescent green color and relatively large size. While not harmful to humans or animals, a bad infestation of Japanese beetles can defoliate a plant in a day.

dainty bess rose with beetle

This pretty ‘Dainty Bess’ rose is just what the beetle likes. Note the two hair tufts on his back end–an identifying mark on Japanese beetles.

Beetles are about a half-inch long with a shiny, two-tone green and tan back. They are distinguished from other beetles, such as the rose chafer, by their tufts of white hair, five on the side and two at the rear. The beetles overwinter as grubs in the soil and may be a more serious threat to turf grass than to plants, but they can fly long distances, so the beetles in your yard did not necessarily hatch there. Adult beetles emerge in July and for the next six to eight weeks go on a feeding frenzy. In the two months she is alive, a typical female Japanese beetle will lay about 60 eggs.

 Treatment Options

If an infestation is not severe, the best approach is to hand-pick the beetles and drop them in a bucket of soapy water, where they will die. You will tend to see more beetles on sunny days. It’s also a good idea start picking and killing beetles when you first see them because the presence of beetles attracts other beetles. Do not squish the beetles, no matter how tempting! It only attracts more.

You can find beetle traps for sale, but their effectiveness is not proven. Because the traps are baited with the scent of geraniums and roses as well as the pheromone of beetles, some researchers believe the traps actually attract more beetles to your yard.

Insecticides can be used on the beetle grubs (in May) and on the adults. However, many popular insecticides, such as those using carbaryl, bifenthrin, and permethrin as an active ingredient, also can be highly toxic to birds, bees and fish. The infestation will not last forever. Whenever you spray, follow package directions carefully and be mindful of possible spread of the insecticide.

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About Tom McKusick 30 Articles
It is the mission of MSHS to serve Northern gardeners through education, encouragement, and community. Through a variety of educational programs, classes and conferences, and by publishing an award-winning magazine, Northern Gardener, MSHS helps its members and the general public to be better gardeners in USDA plant hardy Zones 3, 4 and 5. MSHS’ plant donation network, Minnesota Green, started in 1988, serves the greening efforts of volunteer gardeners throughout the state. Minnesota Green promotes grassroots efforts to revitalize communities by coordinating the donation and distribution of nurseries and greenhouse’s flowers and trees to be planted in public spaces statewide. MSHS was formed in 1866, as an association of fruit growers who took on the challenge of growing apples and other fruits in a northern climate. Two years later, the association became the Minnesota State Horticultural Society to recognize the importance of all phases of horticulture development in rural and urban Minnesota. In 1873, the Minnesota Legislature approved an act providing for the publication and distribution of 2000 copies of all the transactions of the society. 1894 marked the birth of one of the longest continually published horticultural magazines in the country: Northern Gardener, formerly known as Minnesota Horticulturist.