Japanese Beetles Remain Active

Japanese beetles are very active in some locations and should continue to feed for the next 2 weeks. Single beetles do not eat much but an aggregation pheromone will lure more to prime feeding sites. Damage is often heaviest at the top of plants, progressing down as the insects continue to eat.

Figure 1. Severe defoliation of Japanese maple (Photo: T. James)

Figure 1. Severe defoliation of Japanese maple (Photo: T. James)


According to research from the UK Horticultural Entomology Lab, products containing the pyrethroid insecticides bifenthrin (Talstar, etc.), cyfluthrin (Tempo), cyhalothrin (Scimitar), deltamethrin (Bonide Delta Eight Insect Control, etc.), or permethrin (many brands) provided a high level of control for at least 14 days after application. Carbaryl (Sevin) provided a comparable level of control for about 7 days.

Home garden formulations of Pyola (pyrethrins + canola oil) or azadiractin (neem) provided control for about 3 days. Products containing capsaicin, rotenone+pyrethrins, kaolin particle film, D-limonene, or garlic extract were not effective in the trials.

There are some things to watch when following an intense spray program against Japanese beetles during the heat of summer.

  • First, the effectiveness of pyrethroid insecticides decreases as temperature increases.
  • Second, broad spectrum insecticides can have a greater long term impact on natural enemies that they do on pests, so problems may develop with secondary pests, such as mites.

By Lee Townsend, Extension Entomologist

Posted in Forest Trees, Landscape Trees & Shrubs, Ornamentals
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