The Yellow Farmhouse Garden

July 29, 2011

Koganemushi in the Garden

Filed under: Insects — bob @ 12:42 pm

The first Japanese beetle of the season showed up in the garden several days ago.  The beetle actually landed on my arm. That was a big mistake on his part because I immediately tossed him to the chickens.

Those first beetles are forward scouts. Once they arrive, they release a pheromone that attracts other beetles. Before you know it, you have a real problem on your hands.

Sayaka Terada, a garden volunteer at Matthaei Botanical Gardens, told me that in Japan they are called koganemushi, or, in English, “gold bug.” Japanese farmers consider them somewhat of a nuisance because they do some damage on crops such as grapes and soybeans.

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

The beetles are emerging from the soil where they spend much of their lives as grubs.

Picking off the beetles and killing them whenever you find them is an adequate way of keeping their numbers down – if you are persistent.

Japanese beetles, like many other insects, have certain types of plants they prefer over others.  One of their favorites is evening primrose, a type of weed commonly found in and around gardens.  A good strategy is to let the beetles start feeding on the evening primrose; a large number of them will often congregate onto one plant.  You can then kill the beetles without having to spray your garden directly.

Two Japanese Beetles  feeding on Evening Primrose. The green lighting effect is from the early morning sunlight.

Over the counter chemical sprays work well in controlling them but chemicals also kill beneficial insects.

There is promising research at Michigan State University that involves introducing naturally occurring microorganisms into the environment to infect the grubs and reduce their population.  This new method will be different from the milky-spore treatment that is currently available.


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