June is affectionately called “Big Bug Month” by some entomologists (people who study insects). While Japanese Beetles (Popillia japonica) are not the largest insects on the planet, only reaching a size of 7/16ths of an inch, they have become one of the biggest pests in North Carolina because they feed on over 200 plant species.
As the name implies, this insect is not a native to North America. This native of Japan has no natural predators in the U.S. so it has been free to move and expand its territory. First observed in a New Jersey nursery in 1916, these beetles now are reportedly found in 22 States east of the Mississippi River.
This insect is fairly easy to identify with its shiny, metallic green body, bronze colored wings, and six white tufts of hair on each side of the abdomen. The skeletal remains of leaves are all that remains when Japanese beetles finish feeding.
The adult beetles emerge from the soil between June and August. They fly, feed, mate, and then the females burrow into the soil to lay eggs. Eggs are laid in healthy turf where the grubs (beetle larva) will have plenty of delicious grass roots to eat. The grubs lay dormant through winter to begin feeding again in the spring. When they reach the proper size, they pupate into adult beetles. If grub populations are large enough, dead patches of grass with no roots can be found in the lawn.
Control of adult beetles can be achieved by chemical products with these active ingredients: acephate (Orthene), carbaryl (Sevin), malathion (Malathion), or pyrethrins (X-clude).
To control white grubs (Japanese beetle larva) in lawns and turf, use these active ingredients: carbaryl (Sevin), imidicloprid (Merit), and trichlorfon (Proxol/Dylox). Grubs are best controlled in August and September while they are small.
For those who prefer to do things the natural way, there are several biological control methods. Paracitic nematodes, especially Heterorhabititis bacteriophor can be used to control grub populations, and are available at some retail garden centers and online. Milky Spore is a commonly occurring bacterium in soils. It gets into the grubs intestine, and then into the blood where it multiplies until it kills the host. Parasitic wasps introduced from Japan help control the beetle population. Tiphia vernalis attacks grubs and Istocheta aldrichi attacks adults. It is reported that Tiphia vernalis has naturalized here in North Carolina.
Another method is through habitat manipulation. This means keep your plants healthy and strong. A strong healthy plant is not as attractive to Japanese beetles as one that is weak from lack of fertilizer or water. Planting ornamentals that are less attractive to Japanese beetles helps reduce the population as well.
Shawn Banks is a Horticulture Agent with the NC Cooperative Extension Service.