Japanese Beetles

japanese beetle

By Becki Lynch, Linn County Master Gardener
The Summer pest to beat is the Japanese Beetle once again.  One would think with the heat and drought, there would be fewer of them, but, unfortunately, that is not the case.  The Japanese Beetle was first found in the US in 1916, and although the Eastern US has a natural control for them in their soil-inhabiting protozoa, the Midwest is not as fortunate.  They are a serious pest as the grubs feed on the roots of grass, thus killing sections of lawn, and the adults feed on over 300 types of plants.  Although they do not necessarily kill the plant, they severely damage and destroy the foliage and blooms.  Some of their favorites are roses, hollyhocks, linden and crabapple trees. 
In case you’re not sure what a Japanese Beetle looks like, think of a small, square shaped copper/bronze glinted black bug.  You will find them on blooms and foliage quite easily, and one of the easiest ways to control an adult is to simply knock them off into a bowl of soapy water.  It’s quite easy to do this early in the day.  Another method of control is by using a contact spray.  A number are available, and are organic and leave the environment very quickly.  However, they will kill everything they touch, such as bees, so it’s best to use sparingly when beneficial insects are not around.  Some people use beetle traps, but research has found the traps attract more beetles than they catch.  So, if desperate, go ahead, but do not expect a highly successful deterrent. 
Finally, there are some trees that are not attractive to the beetle, such as box elders, lilacs, and oaks, so you can make some choices when choosing your trees.  Unfortunately, many of us have beautiful, mature trees that were present when we moved to our homes, so this step isn’t really an option.
The other method of control is through elimination of the grubs that develop into the beetle.  Look for patches of brown grass areas, and they seem to prefer the roots of strawberries.  The best time to control an infestation of grubs is from mid-July through September through a granular application which will not allow them to develop into the beetle. The beetles emerge in late June to early July and are active for approximately 6 – 8 weeks before they die.  They will lay up to 60 eggs in that time frame, and the grubs will grow to almost 2 inches. 
Thus, now is the time to check out your property and address any problems.  By being proactive this year – perhaps you can get ahead of the problem for next year! 
For additional information, please refer to the article at http://www.extension.umn.edu/distribution/horticulture/dg7664.html.
photo by: Laura Jesse, ISU Insect Diagnostic Clinic

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