Last summer was a bad one for Japanese beetles in my area. Thousands devoured my knock-out roses, green beans, and the leaves on our linden tree.
James Quinn is a regional horticultural specialist at the University of Missouri. He says when you see the first beetles arrive, spray the plants you want to protect with an insecticide.
"If you can get that initial treatment on, it will probably give you about three-weeks of protection. And then if you see them start to see them linger, come back around, treat again," says Quinn. "There’s a number of different active ingredients you can use. Sevin is one that’s very effective, Spectricide triazicide insect killer is a very effective product, and there’s lots of formulations with permethrin, and that also should be effective."
There are drenches available for tree protection. Be careful applying them if the tree is flowering so it doesn’t affect the bees.
If you don’t want to use insecticides, another option is trapping. The jury is out on whether traps are effective, or they call in more beetles telling them the party’s at your house.
"When populations of Japanese beetles are fairly low in the area, then they can work ok because there’s not so many that they overwhelm the traps, and so people will often use traps initially to good success," says Quinn. "But when the Japanese beetles come in in some really daunting numbers, then, the traps almost seem to draw more into your area than the trap will catch."
If you use traps, put them around the edge of your property, away from the plants you’re trying to protect.
Find more tips for managing Japanese beetles