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Natural Resources

Posted on: July 12, 2017

Japanese Beetles Are Back

Have you noticed linden or birch trees with lacy brown leaves? Japanese beetles are the culprits. The Japanese beetles were terrible last summer and they are emerging now. Each year is different,some years we hardly notice the pests. Lindens and birch trees are their favorite trees – along with other shrubs and flowers. If your trees were nice and full and healthy before the infestation, they will likely be just fine long term. The damage definitely stresses them out so any extra care you can give for the rest of the season and the next few years is a help. This means long deep watering in times of drought and going into the winter.

Typically a systemic insecticide (one that lists Japanese beetles and your tree/shrub on the label) is enough to ward them off in each future year. Application must be timed properly so the insecticide is effective in the tree as the beetles become adults and start feeding. (This year, that would have been a few weeks ago.) It is also critical to follow the label and dosing requirements, as these products can kill beneficial insects too, like bees and pollinators. Any sprays on the market typically have a lower residual rate so you’d have to keep spraying. With large trees this can be very difficult.

As soon as you start to see Japanese beetles show up, squish or drown them, as they are attracted to each other. The pheromone traps/bags are not necessarily the answer, as you are essentially calling the beetles over to your yard, and they will stop at other things and chew.

Japanese beetles are definitely a nuisance but typically the trees do survive and leaf back out just as full next year. A more “resistant to Japanese beetle” Sentry Linden tree was offered in this years City Tree Sale and road projects. Researchers and nursery companies recognize that consumers do not want to deal with these pests and have created new trees as a result.

For Japanese beetle management in Minnesota from the U of MN Extension Service follow the link below.
Additional Info...
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