The Rockdale Gardener

Gardening Posts From Rockdale Cooperative Extension

Japanese Beetles; June Invaders

japanese beetles

Japanese beetles emerge in June. Adults feed on leaves while grubs feed on turf. www.forestryimages.org

Japanese Beetle (Popillia japonica) was introduced into the United States around 1916. According to the University of Georgia, they have since spread to infest much of the East Coast from Maine to northern Georgia and inland as far as Indiana and eastern Kentucky. In Georgia, these pests are found as far south as Macon and are often abundant in and around the Atlanta area. Because the adults feed heavily on foliage of a wide range of ornamental plants, fruit trees, vegetable plants, and shade trees, they are very serious pests independent of the damage done to turf by the grubs.

They are related to June beetles, colored a brilliant metallic green with coppery brown forewings. A row of five white spots along the side of the abdomen and a pair of white spots on the top of the last abdominal segment distinguish this beetle from similar species such as the Green June Beetle.

Japanese beetles adults are nearly ½ inch long, broadly oval, thick bodied, with coppery grown wing covers and a metallic green body. Mature larvae are nearly 1 inch long and white, with brown heads. There is one generation a year. Larvae overwinter in soil.

Beetle larvae are called white grubs. More than a dozen different species may damage turf in Rockdale County. All are C-Whitegrubshaped, white to dirty white in color, with brownish head and legs and usually with a darker grey area at the tip of the abdomen. White grubs are extremely common and are only a problem requiring any treatment when they occur in high numbers. Scout for the pest by digging under a section of turf one square foot in size and count the grubs you find. Do this in several places and average the number of grubs you find per square foot. If the number is more than 5 to 10 in non-irrigated turf or 20 in irrigated turf then you may need to treat. Milky Spore is often sold as a cure for grubs. It works very slowly achieving about 40 – 60% control of Japanese beetle grubs.

Adults of this imported scarab beetle feed on the flowers and leaves of many plants. Preferred plants include rose, crapemyrtle, maples, sycamore, birch, cottonwood, linden, mountain ash, and elms. Look for adults on preferred hosts from early June through August.

Weekly application of residual or contact insecticides to host plants in June through July will provide only partial adult control. Liquid Sevin sprayed in the early morning when beetles are inactive can achieve good control. Traps usually are counterproductive and most often attract more beetles than they trap. Place one in your neighbor’s yard for the best control of your beetles. Just kidding. Avoid traps altogether.