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Green Speak

Horticulture topics from gardens to lawns and then some.

Return of the Japanese Beetle

Podcast They're out there. It's only a matter of time before you begin to see their tell-tale signs. That's right I'm referring to Japanese beetles, which typically emerge around the fourth week of June in Central Illinois.

As we have all discovered, control of this exotic new pest is very difficult. Homeowners can go with the approach of controlling the Japanese beetle grubs in their lawn before they pupate and become adults. However, Dr. Phil Nixon, Extension Entomologist, University of Illinois, explains "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."

For controlling adult Japanese beetles, conventional pesticides such as Sevin and Malathion only provide a couple days of control, plus they wind up killing a lot of beneficial insects. On smaller shrubs and flowers, I've had great success with hand-picking. Japanese beetles are more sluggish in the early morning and late evening so that is the best time to pluck them off and drown them in a soapy water mixture.

Rhonda Ferree, states, "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."

For the larger shade trees, particularly the lindens, control is not as easy. Several systemic pesticides are labeled for use to control adult Japanese beetles. Phil Nixon does warn about the dangers of such products saying, "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." Luckily, the Japanese beetle is only present for about three weeks during the summer months, which gives many of our large shade trees time to recover from such damage.

The big question is, "How bad are they going to be this year?" And the best answer to that is we're not sure. Yet, if I had to make a prediction, I would guess numbers could possibly be low due to the drought we had last summer. Japanese beetle females prefer to lay their eggs in moist, open lawns, so if you live in an area with a lot of irrigated turf then I would say expect more of the same.

Following are some great sources of information on Japanese beetles from University of Illinois Extension:

Rhonda Ferree has a blog dedicated to the Japanese beetle – CLICK HERE

HortAnswers – CLICK HERE

A PDF on Japanese beetles – CLICK HERE

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