Ask a Master Gardener: Japanese beetles have yet to reach our area

Q: Do we have to worry about Japanese beetles in our area? My sister in Minneapolis gets her roses totally skeletonized every year.

A: Japanese beetles are a big problem for many Twin Cities-area homeowners. So far they have not been reported in St. Louis, Carlton, or Cook counties, but they have been in Pine and Itasca counties, and we should eventually expect them here. The grubs eat the roots of grass; the adults eat the foliage of many types of plants. Healthy plants usually can recover from the damage. Japanese beetles are about 3/8-inch-long with a dark green metallic head and dark tan metallic wings. They emerge in July and can be around for six to eight weeks.

When they do arrive, the safest way to control adult Japanese beetles is to pick or knock them off your plants into a bucket of soapy water. Japanese beetles are attracted to plants that other Japanese beetles are eating, so early and frequent removal can keep your garden from being the local diner. Pheromone traps also attract hungry Japanese beetles, some from several blocks away. However, they catch fewer beetles than they attract, increasing infestation. Milky spore products also are not effective. Neither is recommended. Well, maybe your neighbors down the street would like you to get a trap and thus attract their Japanese beetles, but traps are not recommended by horticulturalists looking out for your interests.

There are chemical sprays that can be used for severe infestations or grub damage, but they need to be used very carefully and at specific times to be effective and to prevent damage to bees and other beneficial insects.

For now we should just sit back and enjoy our time without this serious pest.

More information on Japanese beetles and their control can be found at: http://blog.lib.umn.edu/efans/ygnews/.

This question has been answered by St. Louis County Master Gardeners, who have been trained by the University of Minnesota as volunteer horticultural educators. Questions can be submitted and additional information found at www.extension.umn.edu/garden.

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