If you spend any time in the yard these days, you are bound to see them. They don’t try to hide. Japanese beetles, half inch long, brown and green metallic bugs are showing up everywhere this time of year.
According to the Missouri Garden Extension, the beetles are not considered a threat yet in the St. Peter’s area, but they still seem to be everywhere.
Japanese beetles attack the yard in two ways.
The Kemper Center for Home Gardening, based out of the Missouri Botanical Gardens, says that the mature beetles typically emerge in this area in June and July and are active for about six weeks.
They feed on low growing plant leaves then move to trees. The Japanese beetles begin at the top of the plant and work their way down. Typically, they feed in groups.
Adult beetles live about one month. Females eat, mate, then lay eggs about two to four inches below the soil surface. The females repeat the cycle during their adult life, until they have laid approximately 40 to 60 eggs.
When the grubs hatch, about two weeks after the eggs are laid, they feed on the young, tender grass roots for the rest of the summer and into the fall. Cold weather forces the grubs below the frost line for the winter.
In the spring, the grubs come to the surface, eat grass, vegetable, and garden plant roots while they continue to develop, then form a pupa in an earthen casing, about one to three inches below the soil line.
Adult Japanese beetle damage is mostly an eyesore and does not harm a plant long term. Adult Japanese beetles are capable of flying many miles as adults, so according to the Kemper Center, adult Japanese beetle control does not ensure less lawn damage.
If you choose to treat the adult Japanese beetles, Kemper recommends two very effective pesticides. Pyrethrum (Neem) can be applied twice, with about four days between applications. Carbaryl (Sevin) is stronger and may be applied twice with about five to nine days between applications.
When treating adult Japanese beetles, it is important to remove the dead beetle carcasses, since the smell of the dead ones will attract more live beetles. As always, when spraying around plants intended for human consumption, take caution.
Treating the grubs, however, will be beneficial for keeping your turf grass in top shape. The feeding grubs damage the grass roots, and roots of ornamentals and vegetables.
Home and garden centers offer a variety of brands of grub killer, which is applied directly to the turf grass. Most are sold in granulated form, but a quick check of indicates that a liquid, spray form of grub control is also available. Merit, a chemical present in several name-brand spray grub control products, is becoming popular. In the St. Peters' area, now through July is the ideal time to apply this product.
Unfortunately, there are few predators for the Japanese beetle. The beetle’s body it too tough for most birds to eat. Toads have been known to feast on the adult beetle, but not in numbers great enough to control the population.
For now, the best defense to keep your yard looking its best is to get out there and curb the grub population.