What you should know if you’re struggling with Japanese beetles

WAUSAU, Wis. (WSAW) – If you’ve been struggling to deal with Japanese beetles, you’re not alone.

It’s estimated that Japanese beetles cause $6-$7 million in plant damage in the U.S. every year. The beetles aren’t too selective in the plants they feed on, and that makes them pretty problematic.

Apples and green beans, raspberry plants and Basswood trees. Japanese beetles like them all. They eat over 300 plant species, which is not normal for most beetles.

They tend to come out in early July, and there are a lot of them feeding this time of year.

“As a non-native species, they really don’t have the predators and parasites and diseases that control the populations of native species of insects and that’s part of the reason why they’re so abundant,” UW-Stevens Point Assistant Dean for the School of Biology, Chemistry and Biochemistry, Paul Whitaker, said.

He says there are a few things that go after these beetles. Skunks will dig up turf in search of beetle grubs. There is also a fly species that targets Japanese beetles. They lay their eggs on the top of the beetle’s head.

“That fly larvae, or maggot, will hatch out of the egg and burrow into the guts of the adult beetle and kill that adult beetle,” Whitaker said. “So that was a fly that was brought in on purpose as a biological control.”

Whitaker says the USDA introduced this fly to help control the invasive beetles. He also says there is a non-stinging wasp that digs into the soil and looks for grubs. It lays its own eggs on the beetle grubs. Then, the wasp larvae eat the Japanese beetle grubs.

“The thought is that predators and parasites and diseases gradually begin to catch up with the beetles and bring their populations under control. So if people can be patient, like on the time frame of a decade, they might see some relief,” Whitaker explained.

If you’re working on dealing with these beetles yourself, Whitaker recommends avoiding watering turf from July to mid-August. That’s when females are looking to lay eggs in damp turf.

Hsu Growing Supply says many people buy neem oil.

“It helps to deter bugs and if it’s ingested, it can harm the beetle that eats it,” Hsu Growing Supply Sales Manager Betsy Heidt explained.

There are many other treatment options, including putting netting around your garden, or going through and tediously picking the beetles off of your plants.

Whitaker says beetleGONE! is 90% effective in deterring Japanese beetles from eating plants, but not killing them.

A UWSP professor says once the bugs emerge in July, they feed for about 2 months

When Japanese beetles are feeding and happy, Whitaker says they release aggregation pheromones. These attract more beetles to the area. Pheromones are also used in traps for these beetles.

Whitaker says these traps may not do what you want.

“Those BAG-A-BUG type of traps, you wind up with more plant damage in the area of the trap than you would if you didn’t have the trap. So yeah, if you buy one of the traps, you want to give it to one of your neighbors, like a block away or something, and they might draw the beetles away from your place,” he said.