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John Fulton

John Fulton
Former County Extension Director

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In The Backyard

Horticulture columns and tips done on a timely basis

Control of Adult Japanese Beetles

Posted by John Fulton -

Application of imidacloprid (Merit and other brand names) and other systemic insecticides is effective in controlling Japanese beetle adults. Although the imidacloprid occasionally doesn't work in a tree to control this pest, it does over 80 percent of the time. However, a soil application of imidacloprid typically takes 6-8 weeks to move completely up to the leaves of large trees. With Japanese beetle emergence typically starting the fourth week of June in our area, the sooner the better for application. This would be a prime option for linden trees, crabapples, rose bushes, and other favorites of the Japanese beetle.

Imidacloprid can be soil-applied either as a drench or by injection. Because imidacloprid is easily tied up on organic matter, mulch and other dead organic matter must be removed from around the base of the tree before a drench application is made. Removal of turf around the tree would also be recommended for a drench. Soil injections should be made deep enough to get below mulch, turf thatch, and other organic matter, but not deeper than 3 to 4 inches. Apply to the soil within 1 to 2 feet of the trunk, where the greatest concentration of fine feeder roots is located.

Just remember, each beetle must eat some leaf to get the insecticide. If a million beetles all take two bites of your linden leaf, there are still going to be a lot of linden leaves eaten. Don't use this treatment on fruit or small fruit trees unless labeled.

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