4 Ecologically Sensitive Ways to Manage Japanese Beetles

August 20, 2020

If you’ve ever seen leaves that look like lacy skeletons, with only the veins intact, you’ve seen the damage Japanese beetles can do. These pests are relentless, invasive, and incredibly detrimental to our ecosystem.

The beetle, originally from Japan, was first discovered in the US (in New Jersey) in 1916. Since then, populations have steadily expanded, and climate change is only making them more of a threat. These beetles are considered the single most destructive pest to local landscapes. They feed on over 300 different kinds of trees, shrubs, grasses, and garden planets, including: elm, birch, black walnut, grape, hawthorn, Japanese maple, linden, apple, mountain ash, flowering cherry, pussy willow, rose, raspberry, and willow. The adults are about ½” long, have metallic green heads and copper bodies. But it’s not just the adults you have to worry about; 90% of the lawn grubs that live in Massachusetts lawns are Japanese beetle grubs, waiting to emerge and feast.

It is important to catch infestations early. Once they start feeding, the release of pheromones and plant volatiles can lead to a feeding frenzy that’s difficult to stop. That’s why many people resort to spraying harsh chemical pesticides to get rid of these pests, but these chemicals are notorious for hurting the environment more than they help it. If you suspect these beetles are wreaking havoc on your land, we encourage you to try one of these more mindful, ecologically-conscious solutions for Japanese beetle management…

Hand Plucking

The simplest (yet most time consuming) way to rid your garden of these beetles is to go outside in the early morning when they’re least active and individually pick them off your plants. Dropping them in a bucket of soapy water (Dr. Bronner’s works great) will quickly kill them. For those with a small, organic vegetable patch, this is probably the simplest way to manage them.

Setting Traps

Most traps on the market are designed to release a sex pheromone and a floral scent to the attract beetles, who end up getting stuck inside the bag or container. But there’s some debate about the effectiveness of these traps. In some cases, they can inadvertently attract more beetles! This is generally the case if you only set one trap, which is why it’s important to set multiple. About 4 traps surrounding the perimeter of your yard are recommended, set at least 500 yards from any highly susceptible plants. Keep in mind that these traps require regular upkeep and the bag of beetles can smell pretty unpleasant, so it may not be the best solution for those with small yards.

Beneficial Nematodes

Treating your soil with nematodes (specifically the species Heterorhabditis, found at gardening centers) can actually help control the larvae and reduce infestations before they’re an issue. Nematodes are parasitic roundworms that eat the beetle grubs (along with 200 other pests) and help keep populations in check. Don’t worry, nematodes quickly die in temperatures over 86 degrees Fahrenheit, making them a safe option if you’re concerned about the health of yourself, children, and pets. The best time to introduce beneficial nematodes is late August/early September.

You can also treat your land with a fungal disease called milky spore, which appears to only target Japanese beetle grubs, but this can be expensive as at least an area of ⅝ mile needs to be treated in order to be effective.

Diatomaceous Earth

This natural powder is made from hard-shelled organisms and is highly abrasive. It gets under the beetles’ shells and eventually kills them. Sprinkling this substance around rose bushes, geraniums, and other highly attractive plants can help stave off beetles, but applying it directly on the insects is most effective.

Of course, if you’re early on in the process of beautifying your landscape, the best way to resist infestation is to plant trees and bushes the beetles aren’t attracted to, like: boxwood, dogwood, forsythia, hemlock, hickory, holly, juniper, lilac, magnolia, mulberry, northern red oak, pine, red and silver maples, and tulip poplar.

If you have questions about organic land care, reach out to us anytime. We are here and happy to help!

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