One of the most destructive pests to home gardens and the green industry is the Japanese beetle. This beetle was originally found in 1916 in New Jersey and has spread throughout much of the United States. You may be familiar with the beetle’s green shiny head and copper-brown wing covers as well as their protruding back legs while they feed on your garden plants. This beetle is known for defoliating or “skeletonizing” plant leaf tissue until all that is left are the leaves vascular tissue.
Hosts
Japanese beetles feed on over 400 species of broad-leaved plants. Some examples are roses, flowering cherry, and zinnias. Not only do the beetles feed on foliage, but the larval stage (white grubs) will feed on root systems of ornamental trees, shrubs, garden crops, and turfgrass. Japanese beetle larvae tend to prefer Kentucky bluegrass, perennial ryegrass, and tall fescue.
Infestation Symptoms
Japanese beetles are known as skeletonizers, meaning that they eat leaf tissue while leaving the veins of the leaf behind. The larvae can kill seedling plants but usually feed on turf grasses. Turn will be off-color as if it is under drought stress. Turfgrass that has been fed on will peel away easily from the soil and the roots have been eaten by the larvae. You will see turf damage in irregular patches.
Control Methods
Cultural control –
Plant varieties that are not susceptible to Japanese beetle feeding like red and silver maple, holly, boxwood, euonymus, flowering dogwood, cedar, juniper, arborvitae, red oak, tulip poplar, magnolia, red mulberry, forsythia, ash, privet, lilac, spruce, hydrangea, and yew. Avoid planting susceptible varieties like Japanese and Norway maple, birch, pin oak, horse chestnut, Rose of Sharon, sycamore, ornamental apple, plum, cherry, rose, mountain ash, willows, lindens, elms and Virginia creeper.
Biological Control –
There are a few different species of parasitic wasp that will feed on Japanese beetle larvae. Introducing these wasps do not seem to reduce Japanese beetle populations when they are already at damaging levels. Introducing wasps could be helpful when beetle numbers are low. These species are Tiphia popilliavora, T. Vernalis, and the winsome fly (Istocheta aldrichi. Parasitic wasps can be purchased online.
Mechanical Control-
There are numerous Japanese beetle traps that can be found on the market. Many of these traps use pheromones to attract the adult beetle. There is data to suggest that this does not significantly reduce grub populations and may cause an increase of foliage feeding if traps are placed near favored feeing plant. Make sure to place traps away from plants that beetles like to feed on.
Chemical control –
There are preventative insecticides available for Japanese beetle larvae. Products labeled for Japanese beetle control will have Chlorantraniliprole as an active ingredient, this can be applied to turfgrass from early April through July. Products containing clothianidin are effective in May
through August. Products with imidacloprid or thiamethoxam can be applied in June through august, and products with halofenozide as the active ingredient can be applied in July.
Products with active ingredients of dinotefuran, trichlorfon or clothianidin are most effective when beetle grubs are in the first and second instar stages, this is between august and September. Remember to read the entire label before using any insecticide and follow all instructions and rules.
Information used from OSU fact sheet HYG-2504-91
