Drenched turf quells beetles

Ladies and gentlemen, introducing The Beetles … Unfortunately it’s not Paul or Ringo, but the Japanese beetle, the most destructive insect pest of turf and landscape plants in the eastern United States, wreaking $450 million in annual damage and control costs.

The all-too-familiar, 3/8-inch long adult feeds on more than 300 different types of plants and lays up to 60 eggs in turf. The eggs hatch into white, C-shaped grubs after 7-10 days. Grubs feed on grass roots for two to three weeks before shedding their skin, or molting, into a larger, more unmanageable grub. It then feeds for three to four weeks before molting into a third-stage grub, spending the winter typically 2-6 inches underground. In the spring, these grubs, which are too large to effectively control, feed for one to two months doing maximum damage. They then enter a nonfeeding stage when they turn into adults, emerging around the Fourth of July in Bangor.

Japanese beetle problems can be reduced, not eliminated, by using a combination of strategies. We recommend against buying Japanese beetle traps because they attract far more than they catch. Avoid killing a beetle with a white egg on its back. The egg will hatch into a young fly, or maggot, that will tunnel into the beetle and kill it. If only a few beetles are present, handpicking may be effective. Protective netting, a more practical alternative available at many local hardware stores, can be used to cover small, valuable plants. Insecticides may also be applied to protect plants. The truly effective insecticides are also hazardous to bees and other beneficial insects.

Research has shown that well-established turf, watered deeply and infrequently instead of daily, is less attractive to Japanese beetle adults looking to lay eggs. Turf can often recover from damage if irrigated or fertilized in the late summer or fall. Treatments may be justified in August if you find more than 10 grubs per square foot using a spade or cup cutter to go through the turf and the 6 inches of soil under it. Beneficial nematodes (harmless, tiny worms) can kill grubs if applied according to the label directions. For information on their use and limitations, visit http://www2.oardc.ohio-state.edu/nematodes/.

A soil insecticide can also be effective. These treatments can protect lawns through spring of the next year but will not prevent next year’s adults from flying in from elsewhere and damaging your turf and other plants. Unfortunately, milky disease, sold under various brand names, has not been effective in scientific trials.

Colin Stewart is a homeowner-greenhouse pest specialist at the University of Maine Cooperative Extension in Orono. To learn more about Japanese beetles or insecticides, contact Stewart at 581-2967 or cstewart@umext.maine.edu.