Japanese beetles were introduced to United States in 1916 and have spread to almost every eastern state since then. They are an incredibly destructive imported pest, eating tree foliage and smaller plants from the top down while exuding a pheromone that attracts more beetles to the feast. Efforts are underway by government organizations to import other insects to help reduce Japanese beetle populations, but until that time, you’ll have to control these beetles the hard way.
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Signs of a Japanese Beetle Problem
Japanese beetle grubs (larvae) can destroy even a healthy lawn. Telltale signs include inexplicable loss of health or brown patches on a lawn, or plants in the area that seem to be turning brown and withering from the top down. It’s safe to assume that if you’ve found one beetle, you’ll find more soon enough.
Mechanical and Biological Controls
- Manual removal: Picking beetles off of plants by hand is one way to control a beetle population. This is best done in the early morning hours, when the beetles are more lethargic. Shaking them off the plant and then putting them in soapy water is easy enough if you have the time and patience for it.
- Traps: Though Japanese beetle traps are quite effective at attracting and killing beetles, they often attract more beetles than they kill. So if you decide to use traps, keep them away from the plants and gardens that you’re trying to protect. Sterling Rescue!® makes a good Japanese beetle trap.
- Insecticidal soap: A gentle insecticidal soap, made by putting 2–3 drops of dish soap in a spray bottle filled with water, will kill Japanese beetles on contact without damaging plants. This is not a permanent solution, but it’s easier than picking the beetles off by hand and may also help break down the aggregating pheromones the beetles use to attract mates.
- Nematodes: For Japanese beetle grubs, lawn treatments containing beneficial nematodes (microscopic parasitic worms) yield good results. Products containing nematodes include BioSafe®, Biovector®, Scanmask®, and Exhibit®, and can be purchased at most quality gardening outlets.
You can control adult Japanese beetles by spraying a mixture of water and a common insecticide such as Sevin® or Orthene® on and around the plants that you’re trying to protect. Follow the directions carefully to ensure a proper ratio, and reapply once a week through peak season (July to September) to help keep beetles off your plants.
Keeping Japanese Beetles Away
As of yet, there’s no tried-and-true way to prevent Japanese beetle infestations, especially since adult beetles will fly several miles in one day to find a proper feeding ground. Planting beetle-resistant plants may help reduce the chances of an infestation. Call your local extension office to find out which plants in your area are least susceptible to Japanese beetles.