Japanese Beetle


What is the Japanese Beetle?

The Japanese Beetle (Popillia japonica) is an invasive insect pest that can cause extensive damage to your favorite trees and shrubs. It eats the tender tissues between the veins of the leaves of plants that it attacks and all that's left of the leaves are the brown, skeletal remains. 


How did the Japanese Beetle get to the United States?

The Japanese beetle is native to Japan. The insect was first discovered in the United States in 1916 near Riverton, New Jersey in a nursery. It is thought that beetle larvae got into the United States in a shipment of iris bulbs before inspections of imported goods entering the country began in 1912. 


Where are the Japanese beetles in Iowa?

The beetle was first confirmed in Iowa in the mid-1990’s in Scott County and has been steadily moving west across the state. Click here for current distribution.


What kind of plants do they eat?

While they have been found to attack a wide variety of plants, Japanese Beetles are especially attracted to sweet smells and, as such, particularly enjoy rose bushes, linden, elm and grape vines. The grubs or larval stage of the insect feed on the roots of turf grass. Thus both life forms are troublesome to the home landscape.


What should I do if I have Japanese beetles on my home landscape?

There are several things to consider:


For a small infestation, you can hand pick or knock beetles into a bucket of soapy water the first beetles you see, usually in late June and July. These first beetles send out pheromones that attract more beetles to the area.


Plant a wide variety of trees, shrubs, and perennials, which is always the best defense against any pest or disease threat. While defoliated trees and shrubs do not look attractive, consider tolerating the damage. Defoliation typically will not kill a tree or shrub, but it does cause stress. Minimize additional stress by mulching around the tree (mulch regulates soil temperature, retains moistures, prevents mower and weed whip damage, and more) and watering if there is a dry period.


Japanese Beetle traps attract the beetles with flowery scents and pheromones and are not recommended, as they attract more beetles than they catch. Put another way, they do more harm than good.


There are insecticides you can purchase at your local garden center to kill the adult beetles, as well as products to control the larvae or grubs. Read directions carefully, and know that treating for grubs probably won’t have an impact on the adults you see the next year and treating for adults probably won’t have a noticeable impact on grubs. Treatments will need to be repeated.


Will my trees and plants survive being eaten by the Japanese Beetles?

Japanese Beetles can cause significant stress to trees and plants through defoliation, but defoliation by itself will not likely kill the plant. Try to prevent additional stress on trees and shrubs by mulching, providing adequate watering during dry periods, and limiting pruning until the dormant season (December- March). Repeated infestations year after year can worsen this stress. Depending upon many other factors and if the plant is defoliated year after year, the trees and plants may begin a slow process of decline. 


For more information see this ISU Extension Horticulture and Home Pest story