Last week, I wrote about two common beetle pests that plague our garden. My main focus of the article was rose chafers. This week I'll focus on the other pest - Japanese beetles. Like their name implies, the beetles are from Japan and were accidentally introduced around 1912 in a shipment of iris. In their native country, the beetles are controlled by natural predators and diseases, not present in the U.S. The adult Japanese beetles are easy to identify with their bright, metallic green head and shiny copper-colored back. They are oval-shaped and about 15 millimeters long and 10 millimeters wide.
The adult beetles appear in early July and can usually be seen munching the leaves of many shrubs and trees through mid-August. Leaves that have been eaten by Japanese beetles are skeletonized, which give them a lacy appearance. The larvae are fat, white grubs found in the soil in the fall and spring. The grubs feed on the roots of grass plants and can cause extensive damage to lawns.
While the adults are clumsy fliers, they can travel up to two miles in search of their favorite plants - which include raspberries, roses, grapes, ornamental maples, beans, apples, pears, and many other fruit trees.
Like rose chafers, Japanese beetles are difficult to control with sprays. No insecticide can be used on a plant in flower as this kills the pollinating insects such as bees. Some report that catnip, chives, garlic, and tansy are natural repellents, as are the remains of dead beetles. These methods do have limited effectiveness.
One of the most effective control methods is to handpick the beetles. While this sounds like a daunting task, handpicking can be quite simple. The beetles tend to drop off of the plant's branches when disturbed. You can catch several beetles at the same time by filling a pan with soapy water, holding it under the plant and gently shaking the plant. The beetles simply fall off into the water. The soap breaks the water tension, allowing the beetles to drown. But, do wait a few hours before dumping out the pan of drowning beetles to make sure they have all died.