Japanese beetles (Figure 1) rarely cause the rampant destruction they inflicted 15 to 20 years ago; their populations now fluctuate around more tolerable levels. However, there are often sufficient numbers to damage plants that are particularly attractive to them, so some management is needed.
Handpicking can be adequate in home landscapes and gardens when beetle numbers are low. Check plants in mid-morning and tap beetles into a container of soapy water. A few happy beetles will draw more; while feeding on a good host, Japanese beetles release chemicals that attract more beetles. While individual beetles do not eat a lot, clusters of them can be very destructive. Don’t give them time to advertise.
Many landscape and garden insecticides can give good contact and or residual control of Japanese beetles. Be sure that all plants being treated are on the product label and the rates are correct. Amounts of insecticides used on landscape plantings may be higher than those allowed for vegetables. Do not directly spray plants in bloom and do not allow spray droplets to drift onto nearby flowers.
- Carbaryl (Sevin, etc.) is still effective.
- Pyrethroid insecticides (active ingredients: bifenthrin, cyfluthrin, cyhalothrin, deltamethrin, or permethrin) can give relatively long term (7 to 10 days) protection, depending on weather conditions and beetle pressure. However, repeated use of these products can contribute to problems with aphids or mites. Monitor closely for developing problems.
- Neem products can deter beetle feeding for 3 to 4 days.
- Pyrethrins also can provide short term protection. Repeated applications will be necessary to protect favored plants.
- Insecticidal soaps and extracts from garlic, hot pepper, and other essential oils usually are not very effective.
By Lee Townsend, Extension Entomologist