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It’s Japanese beetle season

Bob Dluzen
Special to The Detroit News

The first Japanese beetles of the summer showed up in my garden several days ago, which is a little later than I normally see them around here.

Those first beetles are males. Once they show up, they release a pheromone that attracts female beetles. Before you know it, you can have a real problem on your hands as other beetles arrive.

A Japanese friend  told me that in Japan they are called koganemushi, which translates to “golden bug.” While here the beetles can cause widespread damage, in Japan farmers consider them only a nuisance, mostly on crops such as grapes and soybeans.

They are very beautiful insects if you look at them closely and ignore their destructive habits.

Japanese beetles

Japanese  beetles spend most of their lives underground as grubs feeding on plant roots, causing  a lot of damage to turfgrass due to that feeding.  Skunks love to eat the juicy larvae and will dig holes in the lawn looking for them.

Adult beetles emerge from the soil this time of year to breed and to feed on plant leaves and flower buds to sustain themselves while looking for potential mates..

Japanese beetles, like many other insects, have certain types of plants they prefer over others. Roses and grapes are particularly attractive to them but it seems like they will eat just about anything once they get a taste for it.

Picking off the beetles and killing them whenever you find them is a nontoxic way of keeping their numbers down – if you are persistent. You have to be quick though, they have an unique escape method they use to evade predators and gardeners. If the plant leaves are rustled too much or if there is a lot of sudden movement, they will suddenly drop to the ground and get away.

Over the counter chemical sprays work well in controlling them, but be careful using them because chemicals will  kill beneficial insects just as easily as pest species.

One of their favorite wild plants is evening primrose, a weed commonly found in and around gardens.  A good strategy for minimizing damage to valuable garden plants is to allow the beetles start feeding on the evening primrose first,  a large number of them will often congregate onto one plant.  You can then kill the beetles without having to spray your garden directly.

Damage from Japanese beetles

Researchers  at Michigan State University started noticing about ten years ago that Japanese beetle populations were dropping in Michigan. They suspect it is because of a naturally occurring microorganism in the environment that infects the beetles while they are in their grub stage. It is a different  organism from the milky spore disease that has been used in the past to infect beetle grubs.

 As the newer microbe becomes more widespread, beetle  populations will get smaller. Long time gardeners may notice the trend from their own experience.