Japanese Beetles are Back!

By Diane Hampel, a master gardener in Fairfax County who writes a monthly column, The Laurel Hill Gardener, for her community association's monthly newsletter. This article appeared in the July 2010 newsletter. 

Yesterday while I was out on a neighborhood watch patrol with my neighbor she told me she had seen her first Japanese beetle. While I have not seen any in my garden yet, I know that by the time you are reading this article we will be inundated with them.

This garden pest is the one I hate the most and causes me the most problems. My garden is full of the plants they love to feed on.

I will not go into a lot of detail here because most of the information I want to relay to you is discussed in the Virginia Cooperative Extension Publication on Japanese Beetles. Please take some time to read and study this publication to learn about the life cycle of this insect.  The beetles start as grubs that eat the roots of your turf grass and vegetable plants in the garden, so if we can reduce the number of grubs in the soil, we will reduce the number of Japanese beetles feeding on our trees, shrubs and garden plants throughout the community.


Late July or early August is the best time to apply chemical controls for grubs.  This is when the grubs are small and easily killed.  Applying controls at other times of the year is not as effective.  If you want to apply a natural or organic product rather than a chemical control, I would recommend applying milky spore.  It is available in two forms.  The powder form is a one-time application and applied in a checkerboard pattern on your lawn and then watered in.  You can purchase a special applicator for applying the powder.  The second type is a granular form and is easily applied with your fertilizer spreader.  Granules must be applied three times throughout the summer for two years.   The application of milky spore has a higher initial cost than the chemical application, but over time is the least expensive approach.  If many of us in the community apply this product we should see a reduction of the beetles after a few years.  This one or two time application of milky spore can control beetles for 10-15 years or more.

Once the beetles arrive, the best way to control them is to hand pick them and toss them into a bucket of soapy water, which should kill them immediately.  This is hard to do though, if you have 50 million of them in your yard like I have had the past few years!  DO NOT put one of the Japanese beetle traps up in your yard!  Research has shown that this will only attract more beetles to your yard.

I am testing neem oil for controlling the beetles this year.   I have applied neem oil to the plants in my garden that I know will attract the beetles. This includes all of my ferns, astilbe, hibiscus, clematis and cannas.  I plan to spray at 7-10 day intervals over the next 5 or 6 weeks when the beetles are actively feeding.   Neem oil is a natural insect repellant and pesticide made from the bark, leaves and oil from the neem tree, which grows in India.  I have read that if you can control the beetles early in the season, less will flock to your yard.  I’ll report in the next newsletter what kind of success I have this year with this product.   I am also willing to pay any neighborhood kids who would like to hand-pick the beetles from my plants each week!  The only criteria I ask is that they are not squeamish about bugs!

Whether you decide to use chemical or natural sprays on your plants, always remember to READ THE LABEL before applying, and only apply in early morning or in the evening when bees are not actively pollinating plants.  Also do not apply in windy conditions.

Please feel free to contact me if you need further information about Japanese beetle control or other gardening questions.  You can reach me at bandhampel@gmail.com.