Controversy surrounds the use of Japanese beetle traps. Some gardeners say they're useful while others claim they actually attract more Japanese beetles to the garden.
About Japanese Beetles
Japanese beetles aren't native to the United States. They first appeared in New Jersey when they hitched a ride aboard nursery stock from Japan. Without natural predators, they quickly spread and today they are perhaps the number one garden pest. According to the U.S. Department of Agriculture, Japanese beetles are a serious agricultural threat.
Recognizing Japanese Beetles
Japanese beetles are about half an inch long and are a metallic green color, with an almost iridescent quality to the color. They have bronze wings and six pairs of legs. The larvae look like white grubs curled into a C-shape and they are often uncovered when homeowners dig into the lawn. The female Japanese beetle burrows into lawn or soil about three inches below the surface, lays her eggs, and dies. The eggs hatch in early spring and change into pupae, which eat the roots of grass and plants. When they are ready, they transform in late spring into the very recognizable beetle. Beetle activity increases in June and July, peaking around mid to late June in most temperate states.
Japanese Beetle Traps
Mechanical Japanese beetle traps include a bag or basket and a lure with a scent that attracts beetles. The scent contains either a hormone that mimics the scent of the female beetle (thus luring the males) or a sweet odor that fools both sexes into believing desirable plants are nearby. Once beetles enter the trap, they crawl below a rim or ledge and end up in a bag or container. They cannot crawl or fly back out past the rim or ledge and remain in the catch-bag. Homeowners remove the bag and throw it out, replacing the bag with a fresh bag to continue trapping beetles. The beetles die in the trap.
How to Use
Most horticulturists recommend placing traps away from garden areas. The scent released by traps is so strong that it can easily attract beetles from neighboring yards, acting as a magnet for large quantities of beetles. If you place the traps near your prize rose bushes, for example, you may end up just ringing the dinner bell for every beetle in the neighborhood instead of dealing with the population at hand. Placing traps away from infected or susceptible plants guides the insects away to minimize damage.
Be sure to read the directions completely before using traps. The bait lure may contain substances poisonous to humans or animals. Follow package directions carefully and discard used traps well away from areas where curious children or pets may investigate and accidentally come into contact with the bait.
There's a great deal of controversy about using Japanese beetle traps. While the U.S. Department of Agriculture says they are okay to use, research at the University of Kentucky demonstrated that using traps actually attracts more beetles to the garden than it kills. Some gardeners refuse to use them and prefer sprays or other methods. If you do decide to use traps, remember to keep them away from your prize plants and use them only during the active period when you see adult beetles on plants or in the garden. The scented bait loses its effectiveness over time, and it doesn't help to hang the traps out year-round or too early. The scent wears off before beetles seek it.
Alternatives to Mechanical Traps
Integrated pest management (IPM) practices are recommended for better Japanese beetle controls. Such methods include planting trees, shrubs and flowers unpalatable to beetles to repel them from the garden. Good lawn management practices such as using grub control products, which kill Japanese beetle grubs before they can emerge and damage grass roots or garden plants, reduces the quantity of beetles. An organic plant spray containing neem oil provides effective Japanese beetle control too. Sprayed on leaves, it repels beetles for several days. Reapply if it rains or if you water the garden; water washes the neem oil off the leaves.
Manage minor infestations by simply using a coffee can or jar half filled with water and one teaspoon of dishwashing liquid. When you see a Japanese beetle, flick or push it into the container. The soap water makes it impossible for them to escape and they drown. Discard the water and beetles outside when the container becomes full.
Protect Your Garden
Whether you choose to use traps or other control methods, get a jump on beetle season and monitor the garden carefully. Japanese beetle damage can be unsightly or even kill plants. Keep them from decimating the garden through good pest control methods this year.