Get Ready for Japanese Beetle Season

June is the season for roses, for the end of fresh garden lettuce and peas, and the start of tomato season. It's also the start of Japanese beetle season here in Virginia. Here are some recommendations from the Virginia Cooperative Extension on how to handle this pest.

Japanese Beetle Identification

First, know your enemy: Japanese beetles emerge sometime in the south central Virginia area around Father's Day. Some years it's a little before, some years, a little later. The brown beetles have an iridescent sheen to the carapace, or shell. 

The beetles don't migrate, but actually spend the entire year going through their larval and pupal stages in the earth. Around May, the larvae begin to wriggle to the surface. The fat grubs can often be found when digging in the soil, especially lawn areas where the adult beetles like to lay their eggs.

Japanese Beetle Damage

The larvae damage lawns by eating the roots. This turns the grass above brown, often in patches around where the insects are feeding. Adult Japanese beetles land on the leaves of many ornamental plants and eat holes through the leaves, creating a lace-like effect. They love roses, morning glories, and many, many other plants.

Image licensed from Shaka, Morguefile.com license

Good News and Bad News

The good news with Japanese beetle control is that a drought in July and/or August will kill off many of the eggs, thus reducing the population of beetles the following year. I say that's good news because we often get long dry spells at that time of year, which benefit us in terms of insect control.

Another bit of good news when it comes to Japanese beetle control is that the grubs or larval form of the insect are easier to control than the adults. Lawn-care products that promise to reduce or kill Japanese beetles are your best defense.

Natural Japanese beetle control includes Nematodes, specifically entomophagous nematodes, which are said by the Virginia Cooperative Extension to be effective in controlling the grubs.

Now here's the bad news: one the insects reach the adult form, they are difficult to control. Please see the Virginia Cooperative Extension website for detailed information on insecticides to control the adult beetles.

Can You Use Japanese Beetle Lures and Traps?

Nothing seems to generate more controversy than those ubiquitous bag traps you see hanging in people's yards. The traps work using scent lures and a bag. The scents mimic Japanese beetle pheromones or sex scents. When the beetles smell the come-hither scent, they fly to the trap, tumble into the bag, and can't get out. Every few days or weeks, you remove the bags and throw them in the trash, replacing them with fresh bags until the beetle onslaught has abated.

Some gardeners will swear that the traps work wonders. Others swear AT you when you hang up the traps, claiming you've just wasted your money and they don't work. Who is right? We have to go with the Virginia Cooperative Extension on this one. They claim that the traps work to some extent, but can attract more beetles into the area. That makes a lot of sense. After all, the goal of the scent lures is to attract beetles so it stands to reason that a trap may indeed lure more into your yard.

Whether you use the hanging traps or not is your choice, but given the few effective treatments against this invasive pest, a combination of larvae control, traps and planting resistant-species may help.

For more information on Japanese beetle control, please see:

• Virginia Cooperative Extension: Japanese Beetles
• Virginia Tech: Japanese Beetle Pest Management
• Virginia Tech: Managing Japanese Beetles in Corn Fields