Japanese Beetles: Invasion

The Japanese beetles have arrived!  All week, we have been working to control the population and minimize damage.  It seems appropriate to write a little about this pest, and give a few pointers on how it can be controlled in the garden.

History
Japanese beetles are, obviously, native to Japan. In Japan, the beetle is controlled by natural predators.  However, in the U.S. this is not the case and the Japanese Beetle has proved to be a formidable pest.  It was first found in 1916 in New Jersey. Since then, it has spread to almost all states east of the Mississippi, and has found it's way into Minnesota in the 1990's.



Problem
Japanese Beetles damage plants by skeletonizing leaves and sometimes other plant parts, like fruit or flowers.  The larvae feed on grass roots, and can cause serious damage to turf.  Over 300 plants can host the beetles.  In our garden, the beetles seem to prefer roses, fruit trees, grapes, hollyhocks, and a few like milkweed.  In eastern states, the beetle can be controlled by a soil bacteria.  However, it won't survive in Minnesota, so we have had to think of other means of control.  A healthy tree should be able to survive an attack from Japanese beetles, but a stressed or diseased tree may not.

Identification

The Japanese beetle is easy to identify by it's distinct coloration.  It's back is a copper color, while the thorax and head are a glittery sapphire green.  The beetle is about a half inch long.  They spread by flying. In the garden, we find them most often inside of a rose bloom, often in groups of 4 to 8 insects per flower.  If you notice brown patches on your lawn, Japanese beetle larvae may be the cause.  Roll back the sod and look for large, white, c-shaped grubs and a lack of a healthy root system.  

Control
In the garden, we are utilizing two methods of control: Kaolin clay and hand picking.  Kaolin clay is a natural control, and is approved for use in organic production.  We used a backpack sprayer to apply a Kaolin clay and water mixture to our fruit trees and grape vines.  It works as a repellant to many harmful insects, including the Japanese beetle.  When we hand pick the beetles, we put them immediately into water.  A little insecticidal soap will work to kill them in the water, but we have just been feeding them to the chickens on campus instead.  Like I mentioned before, we have been finding them mostly inside of roses.

Pheromone traps are available, but not recommended.  Recent studies have shown that more insects are attracted to the garden than are actually caught by the pheromone traps.

Several insecticides will also work to control Japanese beetles. For more information on insecticide use, check out the Extension website.
UMN Extension: Japanese Beetles

Japanese beetles are in Minnesota to stay.  While there are many control methods that should be utilized by gardeners, there is no way to eradicate them.  In addition to controlling populations, gardeners should practice good horticulture to keep trees, shrubs, and perennials.  Healthy plants are less likely to suffer fatal damage from Japanese beetles. 

For more information on Japanese beetles, refer to the Minnesota Department of Natural Resources and your local extension office.

Images from wikimedia commons