Are Japanese Beetles Eating up Your Yard? This Bug Scientist Has Some Advice

Japanese beetles are considered to be the most devastating plant pest in the eastern half of the United States. Enterlinedesign/Dreamstime/TNS

By Aaron Mudd From Lexington Herald-Leader

First found in the United States in 1916, after accidentally being introduced in New Jersey, the invasive Japanese beetle has been marching westward ever since.

Today, they’re considered to be the most devastating plant pest in the eastern half of the country, but you likely know them as those metallic green beetles that pass through a yard and leave ugly, skeletonized trees and bushes in their wake.

Rose bushes are one of their favorite targets, but they also enjoy several tree varieties, including birches, elms, cherry, black walnut and some maple trees.

Jonathan Larson, an entomologist at the University of Kentucky, knows them well. He also appreciates how deeply gardeners despise them. Japanese beetles can devastate garden crops and strip a tree of its leaves in a matter of days. While your roses may survive an attack, they likely won’t be pleasant to look at.

“They just feel like a Biblical plague almost,” Larson told the Herald-Leader in an interview. “It’s always at the top of the most-hated bug list.”

Larson often deals with Japanese beetles in his job, and he’s trained under a global expert on them, so we thought we might draw on his experience to help you ward off any invasion you’re facing. Here’s a look at the most effective control methods, including whether you should or just crush the bothersome beetles.

Hand Pick Japanese Beetles to Stop Them From Spreading Further

When people have a pest problem, particularly when it involves bugs, often their first thought is to reach for some kind of spray. True, you can easily find effective beetle control products at any hardware store or garden center these days.

That said, you shouldn’t underestimate what you can do with a simple bucket, some soapy water and a little patience. If you’re really just trying to protect a few plants, maybe some roses bushes you really like, Larson recommends going for an evening walk armed with a bucket of soapy water.

When you spot a Japanese beetle, pluck it from the plant it’s been nibbling on and dunk it into the water bucket. Repeat the process until your bucket is full of dead beetles, then dispose of it. Keep it up for at least a few nights or until the beetles stop showing up. It’s generally best to do this around 6 or 7 p.m., Larson said.

If you’d rather not do it yourself, pay your children or a neighbor’s kid to do it.

“I’ve had people that pay their grandkids like a penny a beetle as a bounty,” Larson said. “It is very effective if you’re only trying to maintain a few plants.”

This method works because of how beetles are drawn to feed on plants in the first place.

While you may have heard Japanese beetles summon others of their kind for a chow down, this isn’t actually the case. What’s really drawing the beetles to a particular plant are the stress chemicals the plant gives off while under attack.

Plants synthesize and use chemical compounds to communicate and interact with their environment. Tomato plants, for example, are known to make themselves less nutritious when under attack by caterpillars, forcing caterpillars to cannibalize each other to survive. Likewise, some corn, cotton and tobacco plants release chemical signals to summon parasitic wasps that prey on hungry caterpillars.

The chemical compounds a plant emits while under attack by Japanese beetles are somewhat like a cry for help. Like bloody chum in shark-infested waters, Japanese beetles pick up on this cue and come running, or in this case, flying. So, if you can reduce the number of biting beetles, the plant’s stress response will diminish and you’ll ultimately have fewer beetles on your hands.

Will Crushed Japanese Beetles Draw More With Their Scent?

That’s a persistent myth Larson often finds himself debunking. Female Japanese beetles do use breeding pheromones to attract mates, but they’re mainly drawn to a particular plant because of the stress it’s under due to an ongoing beetle attack, Larson said.

Once a female has mated, she’ll stop producing the pheromones and burrow underground to lay her eggs, meaning it’s generally OK to smash a beetle you happen to find crawling around your home.

Be Careful About Using Traps for Japanese Beetles

Maybe you have a large beetle infestation and hand-picking them off of your bushes and trees isn’t practical. In that case, you might consider using a store-bought bag trap for Japanese beetles, but Larson cautions against using those.

“We try to push people away from using those near the plants they want to protect,” Larson said. As he explained, the bag can only contain so many beetles, and if a full trap is within 30 to 90 feet of a plant you want to protect, it could become a target for the remaining beetles drawn to the area by breeding pheromones.

“At that point, now they’re just kind of milling around your landscape looking for things to eat,” Larson said. “If you have a large plot of land and you can put (the trap) far away from plants that you want to protect, that is something that can be helpful.”

Larson has also seen people adapt the traps for their own needs. This includes:

• Rigging the trap so beetles are dropped into a 55-gallon drum
• Setting up the trap in a chicken or guinea fowl yard
• Floating them out to the middle of retention ponds and lakes for fish to eat

“There are adaptations, but it’s not something that you want to tie to your rose bush or put them next to your birch tree because you’re going to end up with more damage,” Larson said.

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