The Japanese beetle (Popillia japonica) is an invasive species introduced to the U.S. from Japan in the early 20th century. With no effective natural enemies, it has since become a wide-spread, serious turf, landscape, and garden pest east of the Mississippi River. The adult beetle feeds on a wide variety of trees, shrubs, annuals, and perennials (over 200 species), eating flowers, and the leaf tissue between veins (skeletonizing), and often causing significant damage. The larvae (grubs), feed on roots of turf grass. When populations are high, large patches of grass will wilt and die.
Understanding it’s life cycle is the key to gaining good control of this insect. The 3/8” long adult beetles, which have metallic green bodies with bronze outer wings, emerge from pupae in the ground in late June-early July. They immediately begin to feed, damage plants, and mate. After mating, females fly from the food source to lay eggs in moist, sunny turf. Eggs hatch during the next several weeks and emerging larvae feed. The “C” shaped white grubs continue to feed and grow into the fall, maturing to a length of 1”. As the cold weather approaches, the grubs stop feeding and burrow deep into the soil where they overwinter. In spring, they return to the root zone to feed for several weeks, and then pupate. The entire life cycle takes about one year to complete.
On a given property, adult Japanese beetles tend to cluster to feed and mate on a handful of favorite plant types such as rose, plum, crabapple, Rose of Sharon, grape and others. Focusing your control measures on these plants can have a significant impact on the beetle’s population. During the early morning or late evening, when temperatures are cool, clustered adult beetles are sluggish and easy to kill by knocking them into a jar of soapy water. There are many insecticides, both “natural” and “chemical”, that are effective in controlling adult Japanese beetles. If spraying is necessary, choose the least toxic method that is practical, and follow the directions on the label. These insecticides are non-selective and will kill bees, other pollinators, and predators. Do not spray when pollinators are present! They are in decline world-wide, and are crucial to food production and our survival. Encouraging birds to visit your property can also reduce adult beetle populations. Japanese beetle pheromone and floral scent traps are very effective at attracting and catching Japanese beetles from distances of up to 5 miles downwind. Unfortunately, they often have the undesirable effect of increasing the beetle population, and the corresponding damage, in the vicinity of the trap. If you decide to use traps, site them well away from lawns and favored plants (yours and your neighbor’s).
Larval Japanese beetles are most vulnerable to control treatments when they are young and small, shortly after hatching. Observation of frequent adult female beetle flights to lawn areas indicates the potential for high grub populations later. Sample several 1 sq. ft. by 3 inch areas in your lawn by cutting and then pealing back the sod in order to count the Japanese beetle grubs. Consider spot treatment if counts greater than 10 grubs per sq. ft. are observed. If brown or dead areas appear in your lawn in late summer (Aug.-Oct.), check the margins of those areas for grubs. If grubs are the cause of the damage, consider spot treating the affected areas rather that treating the entire lawn.
Direct treatments fall into two general categories: chemical and biological. Chemical treatments are very effective in killing grubs when used properly, and are fast acting. When severe damage to your lawn is probable, their use may be necessary. However, they are non-selective, may persist in the environment, and have potential impacts to humans, pets, wildlife, and water supplies. Biological controls usually take more time to work, but are more selective, and have fewer impacts on non-target organisms. Biological controls include: B.t. galleriae (Bacillus thuringiensis galleriae), a naturally occurring soil bacterium, specific to Japanese beetles, used as an insecticide, Milky Spore (Bacillus popilliae), spores of a bacterium that specifically infect beetle grubs, used as a soil inoculant, Insect-eating nematodes (parasitic round-worms) that attack grubs, applied to turf, and parasitic wasps that lay eggs on grubs (hatching larvae eat the grubs). Contact your local agricultural extension office for more detailed control recommendations. You can find yours at http://www.csrees.usda.gov/Extension/. With all insecticides, read, understand, and follow the directions on the label. The label is the law!
Habitat manipulation may also help reduce Japanese beetle populations. Allow your lawn surface to dry out between waterings to deter females from laying and to desiccate and kill Japanese beetle eggs already present. Create bird habitat: food, cover, nesting sites, and water. Some birds feed on grubs, adults, or both. Encourage other predators by keeping pesticide use to a minimum. If possible, disperse or remove favored food source plants on your property. Keep your landscape plants healthy and treat or remove unhealthy plants. Clean up over-ripe fruit. Consider reducing the size of your lawn.
The Japanese beetle is here to stay. Taking an informed and multifaceted approach to control will minimize damage to your property and neighborhood while protecting your environment at the same time.
