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Japanese Beetle News

Current information for homeowners and agricultural producers

The Management of Japanese Beetles Begins Soon

It is not too early to begin preparing for Japanese beetle problems. "It is too early to tell how bad the Japanese beetle problem will be this year," says Rhonda Ferree, extension educator in horticulture with University of Illinois Extension.

Here are some tips from Dr. Phil Nixon, Extension Entomologist, University of Illinois, for starting early to help keep Japanese beetle damage as low as possible this summer.

Even though you may dig up some grubs while gardening, now is not the best time to control grubs, including Japanese beetle grubs. These grubs will feed for a short time this spring and then pupate. Grub control products will not be as effective when the grubs are in the pupae life stage.

However, if your turf is being severely damaged this spring and you actually find the grubs present grub control products might be helpful if applied before the pupae stage. If you can pull large sections of your turf up like a carpet and see at least 12 grubs per square foot, a lawn grub treatment is recommended. This threshold is the same for later in the summer when grubs will do more damage if they are present. As always, please read and follow label directions.

Dr. Nixon emphasizes an important point, "Just because you control grubs in your lawn does not mean you will reduce the population of the adult beetles in your yard this summer." "The beetles can fly for several miles, so there will be just as many on your plants whether you treat for grubs or not."

Japanese beetle adults typically emerge the fourth week of June in central Illinois. They feed for about six weeks, flying to new hosts every three days.

Control of the adult beetle is difficult and challenging since they move frequently. Generally pesticide sprays, such as Sevin and Malathion can reduce damage for two to several days, but several applications are required to maintain control.

Some home gardeners find picking them off by hand every couple of days can be just as effective as spraying. Ferree says that, "If you can keep feeding damage to a minimum when they first arrive, it is likely you will have less damage overall."

When disturbed, the beetles fold their legs and drop to the ground. Hold a can containing rubbing alcohol or water with detergent below the infested leaves. The beetles will drop into the container and be killed. Prized roses and ripening fruit can be protected by covering with floating row covers.

To date, imidacloprid (Merit, Bayer Advanced tree and shrub insect control, and other brand names), and other systemic insecticides are labeled to control adult beetles in certain plants. However, recent research has found that since these products last a long time in the plant and kill all insects, they are a serious threat to our pollinator populations. "These highly systemic insecticides have been increasingly shown to move into the flower pollen of various plants where they are picked up by pollinating insects including honey bees and bumble bees." "Until we know more about translocation into pollen in various plants, it is prudent to avoid these insecticides in applications to plants attractive to pollinators."

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