The first recorded sighting of Japanese beetles was in the 1970s, and since then, this pest has wrought destruction on gardens throughout the eastern United States. Originating in Japan, where it has an abundance of natural predators to keep it in check, the Japanese beetle faces few predators here in the United States.
What does Japanese beetle damage look like?
Adult Japanese beetles are recognizable by their iridescent exoskeleton and orangey-green wings. The larvae look like small fat grubs in the soil, typically residing 2-3 inches below the surface.
Japanese beetle larvae feed on the roots of grasses and plants, causing them to die. Adult Japanese beetles feast on the foliage of fruit and ornamental trees and shrubs, and can defoliate a tree or shrub rather quickly.
Ways to Control Japanese Beetles: Mechanical Methods
The best way to control Japanese beetles is to plant beetle-resistant varieties. There are a number of shrubs and herbaceous perennials that are less palatable to the beetles, and aren't as likely to be decimated. Having a diverse selection of resistant plants in your garden is the best way to control these pests.
Japanese beetles are less likely to target healthy plants. Be sure that you are fertilizing and watering your trees, shrubs, and perennials so that they are hardy and strong enough to withstand a Japanese beetle invasion.
Traps are a popular method to control Japanese beetles. We recommend placing these traps far away from your garden, as they attract beetles. Traps have only been shown to capture about 75% of the beetles who approach them, so having a multitude of traps placed around your property perimeter is best.
If you come across white grubs while digging in your lawn or garden in the spring, dispose of the grubs in a bucket of soapy water. Similarly, when the beetles emerge in the summer, pick them off of the plants and dispose of them in soapy water. Resist your squeamishness and pluck those beetles off, smoosh them between your fingers, and dispose of them.
Ways to Control Japanese Beetles: Biological Methods
Biological methods of control are less likely to adversely affect beneficial organisms (think: pollinators) than chemical methods, and some have longer-term effectiveness at beetle mitigation. For biological controls, it is best to target the beetles in their larval stage, as it is when they are actively feeding and growing.
Milky Spore is made up of the spores of Bacillus popillae, which when ingested by the beetle, infects the gut cells eventually leading to death. It is best applied throughout your yard and garden in the late summer to early fall, when grubs are actively feeding. Another benefit of Milky Spore is that it continues to populate the soil once excreted by an infected beetle or larvae, wreaking havoc on Japanese beetle populations for multiple seasons.
Bt (Bacillus thuringiensis) is also a popular biological control. Bt must be ingested by the beetle larvae in order to be effective, you can apply it to your lawn as you would any other pesticide in the summer or early fall.
Ways to Control Japanese Beetles: Chemical Methods
When using chemical pesticides, always follow directions closely to reduce negative effects of pesticide usage on waterways, beneficial organisms, and soil health. Please also be aware that many chemical methods are not safe for children or pets, and should not be used on anything they may ingest or come into close contact with. If applying the insecticide on the ground, wait until it has fully dried and absorbed before letting children play in that area.
Below are the recommended chemicals to use to target adults and larvae. Choose products with the active ingredients listed below. Always follow the directions on the bottle when spraying.
Chemicals for Adults:
Imidacloprid
Bifenthrin
Carbaryl
Cyfluthrin
Deltamethrin
Permethrin
Chemicals for Larvae:
Halofenzide
Trichlorfon
Japanese beetles are a pest that is here to stay. While it can be disheartening to watch your garden get eaten, following best practices with planting, fertilizing, and spraying will mitigate the damage they do.