How to Get Rid of Japanese Beetles

The end of June and beginning of July is when Japanese beetles emerge from the ground in Minnesota and feed on our garden plants for the next two months. While the damage caused is usually cosmetic, large infestations can stunt growth, destroy flowers, and reduce vegetable yields.

Important Things to Know about Japanese Beetles

• Japanese beetles overwinter as grubs beneath lawns and pastures. The grubs feed on roots.
• The beetles can fly several miles in search of food. Killing grubs in your yard does not reduce the number of beetles in your yard.
• They are active and feeding in July and August.
• Japanese beetle damage to plants is usually cosmetic only. If you do nothing about Japanese beetles all of your plants are likely to survive, though you may lose rose flowers and vegetable garden yields. Very heavy infestations can damage plants.
• The damage from Japanese beetle feeding on plants releases a scent that attracts other Japanese beetles. So the more damage they do, the more of them that will be attracted to your plants (and specifically to the plants that are already being eaten).

While no one is very fond of the iridescent beetles, in most cases you don’t actually need to do anything about them. If you can tolerate some scraggly-looking leaves you can choose to just coexist with Japanese beetles.

But if you suffer heavy infestations that are damaging your plants, or you just don’t want to tolerate the beetle damage, there are several ways to deal with mature beetles. In all cases though, the key is to deal with them early.

How to Get Rid of or Kill Japanese Beetles

• One of the best ways to manage Japanese beetles is to physically remove them from plants. Fill a small bucket or jar halfway with soapy water and pick beetles off plants, or flick them into the jar. You can do this anytime, but early morning is easiest when the beetles are still sluggish.
• You can also use insect netting to cover plants that are attracting large number of beetles to keep them away. Keep in mind that if you cover veggies you’ll also prevent other insects from pollinating your plants.
• Do not use Japanese beetle traps. While these are effective at killing impressive numbers of Japanese beetles, research at the University of Kentucky showed that these traps actually attract more beetles than they kill — the smell used to lure the beetles into the trap is so effective it lures huge numbers of them into your yard, many of which then decide to feast on your plants.
• If you want to kill Japanese beetles but physical removal isn’t practical, there are several pesticides that can work for different lengths of time. Keep in mind that pesticides can kill beneficial insects like bees and butterflies and can be harmful to people. You can read this U of M Extension resource on insecticides that can be effective against Japanese beetles.

Remember that Japanese beetles are attracted to leaves damaged by other Japanese beetles. The key to prevention is to start picking them off early, before very large numbers are attracted to your plants. Once you have a very large infestation, you may no longer be able to effectively manage them.

For example, there used to be a large collection of roses at the Washington County Fairground, at what is now the Fairest Garden managed by the Washington County Master Gardeners. The Japanese beetle damage became so severe that it wasn’t practical to maintain the rose garden and now only a few rose bushes remain.

How Many Japanese Beetles Will There Be This Year?

Japanese beetle populations vary greatly from year to year. One of the main variables impacting the population is the soil conditions when the beetles burrow underground and the new generation of eggs hatch. Drought conditions in mid to late summer can harm the turf grass that the larvae feed on and reduce Japanese beetle populations the following year. Healthy lawns with plenty of rain tend to bring about larger populations the following year.