Japanese beetles: Double trouble for gardeners
Posted in Pests & Problems,Bugs
Assorted beetles account for 40% of the world’s insect population, but of the 350,000 known beetle species, it is the Japanese beetle that strikes the most fear in the hearts of American gardeners. After hitching a ride to the United States from Japan in the early 1900s, this pest remains rampant for lack of natural predators.
of turf grass. Some grubs are still visible
in the soil where the dead grass has
been peeled up.
Identifying Japanese beetles
Japanese beetles are easy to identify. About ½" long with a hard shell, the adult beetle has a shiny, coppery body and iridescent green head. It is active for about 6 weeks every summer throughout the Northeastern and mid-Atlantic regions of the United States and into the Midwest and parts of Canada. Its diet includes the leaves of up to 300 kinds of plants. The larval stage attacks underground, on the roots of grass. Laid in summer by the adults, the eggs hatch into fat, white, C-shaped, worm-like creatures (grubs) that feed in late summer, early fall, and early spring. Each female can lay as many as 60 eggs. In severe infestations, grubs can kill off whole patches of lawn. The damage is most noticeable in early fall.
The adult beetles pupate and emerge from lawns, gardens, and grassy fields mostly in late June. For the next 4 to 6 weeks they feed, skeletonizing the leaves and sometimes flower buds of such favorites as fruit trees, roses, grapes, crape myrtles, cannas, and raspberries. The beetles mate during this time. As the weather cools, the dropped eggs become grubs that burrow about 6 inches deep into the soil, where they spend the winter in suspended animation. As the weather warms in spring, grubs feed for a few more weeks (on grass roots) before pupating into new adult beetles that repeat the cycle. Green June beetles, masked chafer beetles and Oriental beetles also feed on lawn roots but are not as destructive or widespread as adults.
How to control Japanese beetles
on roses while they mate.
Non-chemical controls include protecting plants with floating row covers or fine mesh as a blanket. You can also hand pick the beetles, either squishing them or dropping them into a bath of hot soapy water or rubbing alcohol. An organic spray of neem or mint oil works too. One other popular approach is placing Japanese beetle traps in the yard. These hanging plastic traps are baited with scents that attract the beetles. Most research, however, shows that the traps attract more beetles into an area than they capture, usually leading to increased landscape damage. Encourage your neighbors to use the traps to draw beetles away from your property! The traps can be effective if many people use them in a concentrated area. Another alternative for lawns is to introduce “milky spores” that target Japanese beetles. Nematodes (microscopic organisms) may also be introduced to reduce grub populations.
Effective chemical sprays for adult beetles include cyfluthrin, bifenthrin, permethrin, and carbaryl. In late summer and early fall apply trichlorfon and carbaryl to control the newly hatched young adults. Control the grub stage in lawns with insecticidal products containing imidacloprid, halofenozide or clothianidin.
