Robyn Stewart
When I was growing up, my mother had a variety of rose bushes planted in our houses’ landscape. Most years, I would play in the yard and watch these metallic green and copper beetles in the roses and on the leaves of the rose bushes. These beetles, called Japanese beetles (popillia japonica) are a destructive invasive species found throughout the eastern United States.
The Japanese beetle originated in Japan but was first found in the US in 1916 in New Jersey. Despite efforts to control this pest, they infect about half of the contiguous 48 states and continue to spread across the country. The beetle is a serious pest of a huge variety of plants, including roses, grape, linden, apple, cherry, birch, marigold, corn silks, and more. They feed on over 300 different plant species. Feeding damage appears as missing tissue between the major veins of the leaves, making them look lace-like. Feeding damage can cause leaves to brown and fall off of the plant. Mature trees, shrubs, and ornamental plants can tolerate feeding without long-term injury. However, feeding damage will ruin blossoms on flowering plants, reduce yield from fruits and vegetables, and can kill young or unhealthy plants. The white grubs of the Japanese beetle feed on the roots of grasses and can cause significant die off in lawns and turf. The threshold for treatment in home lawns is less than 10 grubs per square foot. Be aware that white grubs can attract insect-feeding animals like moles, skunks, and armadillos, which may dig up and damage turf.
Adult Japanese beetles are usually about ½ an inch in length, metallic green in color, with copper or bronze wing covering. They have five white stripes down the sides of their abdomens and two white patches on the back/tail of their abdomen. Japanese beetle larvae (also known as white grubs) are white or cream-colored with a tan head. Their legs are easily seen and they vary between 1/8 in to 1 in in length. The white grubs are hard to identify without examining their spine pattern and abdominal hairs. The Japanese beetle has a one-year life cycle. Adult females lay their eggs (up to 60 of them) in June and July. After 8-14 days, white grubs emerge in the soil and spend 10 months underground, feeding on roots and organic matter. After their 10-month growth stage in the soil, adult beetles will emerge in early June and live between 30-45 days. Females lay their eggs during this time and the cycle repeats.
Control of Japanese beetles may not be necessary for some plants, but others are succeptible to long-term damage and loss of yield. Adult beetles prefer plants in direct sun and typically will congregate in masses. Hand picking the adult beetles off your plants can be effective if you catch them early in the season and in lower numbers. Simply pick the beetles off your plants and drop them into a bucket of soapy water. For larger infestations you can consider using an insecticide with carbaryl, malathion, or imidacloprid as an active ingredient. You may need to spray every 4-7 days for effective control during heavy infestations. If you are using insecticides, be sure to follow all labeled recommendations for waiting period on edible plants and produce. One last thing- pheromone traps can be effective at trapping Japanese beetles, but the pheromones will attract additional pests to your yard which can be counterproductive for long-term control.
If you have any questions about Japanese beetles, please reach out to us at uge3181@uga.edu or 706-359-3233.
