One of the most destructive garden insects is the Japanese beetle, a six-legged creature about one-half-inch long with copper-color wing covers and a metallic-green head. It has a voracious appetite for flowers, fruit, and foliage, and dines on hundreds of different plants from birches to poison ivy. The species feeds in groups, quickly stripping a rose of its blooms or reducing leaves to a lacy skeleton. To make matters worse, adult female beetles seek out the best grass available in which to deposit their eggs. Within two weeks white grubs emerge and start feeding on grass roots, causing areas of the lawn to turn brown and die. Japanese beetles overwinter as grubs burrowed about ten inches into the soil; when the soil temperature warms up in spring, they move close to the surface and feed for a short period before pupating and becoming adult beetles.
In their native Japan, the beetles cause only minor damage because their population is controlled by natural predators. Not so in the United States: Even though they are a favorite food of skunks and moles and are eaten by many birds, there always seem to be plenty of grubs around. While adult beetles show resistance to pesticides, the grubs are killed, but often at the risk of harming earthworms and beneficial insects. Fortunately, there is a wealth of weapons in the organic arsenal. Milky spore disease, a naturally occurring soil bacteria (Paenibacillus popilliae), kills beetle grubs while not harming valuable insects. It is sold in a powdered form that is spread on the soil and may control grubs for 15 to 20 years.
The adults may travel up to five miles for a meal. The presence of beetles on a plant attracts other beetles, so picking the early arrivals from plants will reduce infestation. Pheromone traps catch lots of beetles but draw in many more that are never caught. Place traps at least 30 feet downwind from the plants you want to protect. Botanical sprays containing pyrethrin, garlic, or neem oil will reduce Japanese beetle damage, as will planting chives, garlic, tansy, and other repellent plants among vulnerable plants. Using one or more of these safe controls will help protect birds, earthworms, and beneficial insects, and soon will have you saying sayonara to this garden troublemaker.