Look for beetles in your yard and garden starting in late June and early July. Start management when they first appear. Damaged leaves attract more beetles so minimizing beetles on plants should mean fewer beetles will be attracted to them.
Japanese beetles feed for six to eight weeks so it is important to continue management until their numbers decrease. Once they are present in large numbers, managing them becomes more difficult. Most feeding is finished by mid to late August.
Check your plants daily and remove any beetles that you find to minimize feeding damage. Remember beetle-damaged leaves emit air-borne chemicals that attract more beetles. By physically removing them, you’ll reduce the number of new beetles attracted to your plants.
Physically removing beetles can be a practical and effective management practice for smaller landscapes or a few plants, especially when only small numbers of Japanese beetles are present. Handpick or knock the beetles into a bucket of soapy water to kill them.
The best time to remove Japanese beetles is in the evening or in the morning when beetles on the plants are still cool and sluggish. However, anytime that it can be done is still useful.
Physical barriers – In some cases, it is possible to protect plants with fine netting to prevent beetle damage. However, do not cover plants in bloom that require pollination (i.e. fruits) as this will prevent pollinators from reaching them. Instead, handpick beetles until the plant is done blooming and starting to set fruit, then cover it.
DO NOT USE JAPANESE BEETLE TRAPS – Hanging a trap in a home garden is not an effective way to protect plants. And they may attract more insects to your yard. The traps attract beetles using synthetic female sex pheromone and a blend of chemicals with a strong floral odor. They were developed by researchers to monitor for the presence of Japanese beetles so that management strategies could be implemented.
While these traps can collect an impressive number of beetles, research at the University of Kentucky has demonstrated that more beetles fly toward the traps than are caught. This usually results in more damage to nearby gardens and landscape plants than would have happened if no traps were present.
If physical removal and barriers are not practical or you wish to supplement non-chemical management, you may choose to use an insecticide to protect valued plants. Remember that insecticides can pose significant risks to beneficial insects, including pollinators, as well as birds, fish and mammals.
Low risk insecticides are products containing pyrethrins (e.g. Pyola®) are somewhat effective contact insecticides provided they are sprayed directly on the insect. Repeat applications are necessary.
Neem oil is effective for several days but repeat applications are necessary. Neem oil helps deter Japanese beetles but is less effective when large numbers are present. This product is low risk to bees and other beneficial insects.
Bacillus thuringiensis galleriae (e.g. BeetleGone, BeetleJus), derived from soil bacteria, is moderately effective against Japanese beetle adults, giving one to two week’s protection. This product is not toxic to bees and other beneficial insects. Bacillus thuringiensis galleriae is only available from online sources.
Several effective, longer lasting insecticides are available for treating Japanese beetles. Chlorantraniliprole (Acelepryn®) provides two to four weeks protection, and is low risk to bees. Pyrethroids, including bifenthrin, cyfluthrin, lambda cyhalothrin, and permethrin, last about two to three weeks. Carbaryl or acephate will provide one to two weeks’ protection. Caution: pyrethroids, carbaryl, and acephate are toxic to bees and other pollinators.