Controlling Japanese Beetles
Without Use of Chemicals
Frederick County Master Gardener Program
Japanese beetles, which become active in late June and stick around through August, are a major pest of both agricultural and landscape plants, as anyone who grows roses or grapes in this area can attest.
One reason the beetles are so successful at turning healthy plants into disaster areas is that they are an introduced species with no natural enemies in this country. (New Jersey has the dubious distinction of being the first place in the US where
Japanese beetles were discovered.)
Some 80 years after their initial introduction, they have spread until they cause nearly a half-billion dollars of damage each year. Organic gardeners have basically three types of controls at their disposal: biological controls, traps, and
Most people think of milky spore when they think of biological controls for Japanese beetles. Milky spore is a bacterium that infects the beetles when they are living underground as grubs. Milky spore will work under the right conditions, but it has
several drawbacks. First, it takes a relatively long time to work, as the infection spreads slowly
through the beetle population. Second, it's expensive. Third, and most critical, it only works locally. Japanese beetles can fly up to five miles in search of food, so you must either have a very isolated site or have neighbors who are willing to
treat their properties as well. If not, you won't even have the satisfaction of feeding your own Japanese
beetles: you'll be feeding someone else's. There are other bacteria and parasites available: contact your Maryland Cooperative Extension agent for more information.
Japanese beetle traps, widely available in garden centers and hardware stores, use an odorant to attract beetles, which are highly motivated by smell. They will trap beetles. Unfortunately, unless you have lots of traps located well away from the
plants you want to protect, they may do more harm than good by attracting more beetles than you would have otherwise had. A area-wide trapping program is a good idea, if you can coordinate it with your neighbors.
I personally find a good deal of satisfaction in hand-picking beetles. You need nothing more complicated or dangerous than a plastic tub (the ones used for pre-packaged salads or dairy products are great), some warm water, and some liquid dish soap.
(The soap lowers the surface tension of the water so that beetles can't breath through the little air
holes along their abdomens.) Put a teaspoon of soap in a cup or so of water, don your beetle-hunting hat, and go forth. If you don't relish the idea of handling scrabbling beetles (and who does?), don't worry.
Beetles tend to do a "drop and roll" when disturbed, and will obligingly fall into your tub once you get the knack. The best times for beetle picking are morning and late afternoon - during midday, they're very alert and active, making it harder to
get them to take a swim in your above-ground beetle pool. Garden writer and organic rose gardener Liz
Druitt likens the thrill of beetle-picking to that of hunting ducks at dawn. Remember that beetles attract beetles, so each one you remove makes your plant that much less likely to be attacked. Good luck!
Read other articles on ecological gardening & native plants
Read other articles about controlling insects & garden pests
Read other articles by Marc Monefusco