Do you have Japanese beetles in your garden? I’ve had them for many years now, and I’ve tried several solutions for dealing with them. I'm happy to report that I’ve found a solution that helps. “Helps” is the key word. This method doesn’t eliminate them, but it definitely reduces the number.
Before we discuss what's worked, what have you tried?
Methods I haven't tried:
- I've never used beetle traps because most sources say they actually attract more beetles. Apparently, the traps (treated with flower scents and pheromones) and the dying beetles (also releasing pheromones) draw more beetles in.
- I don’t use insecticides in my garden, so that option was off the table. Plus, they have to be regularly re-applied, and even the “organic” ones are harmful to other insects and pollinators. (With that said, I do use organic neem oil on indoor plants.)
- Diatomaceous earth is another method—but it, too, can be harmful to monarch caterpillars and other garden critters. So, again, not an option I was willing to consider.
- Applying nematodes is another method some gardeners recommend but one I haven’t tried. Several issues here: they have to be applied at certain times of day and certain times of year, they must be a specific species to be effective at eliminating Japanese beetles and the soil and soil moisture must be optimal for them to work.
Methods I have tried:
- Soapy Water — With this method you can simply pick the beetles off the plants and drop them in the bath, or shake them off the plants into the water. Mix a couple tablespoons of dish soap with water in a small (approx. two cups) container. Empty beer or soda cans work well because the beetles have even less of a chance to escape. The soapy solution kills the beetles—they drop to the bottom and drown before they have a chance to release pheromones.
- Soapy Spray — You can mix the same ratio of dish soap with water in a spray bottle, and spray it on your vulnerable plants. The problem with this method is that you’re likely killing and repelling beneficial insects at the same time. So, while I've tried it, I don’t feel good about it.
- Stomping — If you only have a few Japanese beetles (other methods are working but the beetles aren’t eliminated), you can pick them off and quickly stomp them. This destroys them fast before they have a chance to release those pheromones.
- Companion Planting — Some plants, like garlic, scallions, marigolds and catnip, tend to repel Japanese beetles. Try interplanting these repellents among other plants in your garden to help keep beetle numbers lower.
- Milky Spore — This method works best for me. I’ve been using it for a few years now, and it seems to have significantly cut down on the number of Japanese beetles in my garden. The trick is that you need to place it in the garden in late summer or early fall (late August-September). The two main reasons? Ideal soil temperature for effectiveness is 60 to 70 degrees, and it only works on the grub stage of Japanese beetles, which are more active, close to the surface and prevalent late in the season.
Since milky spore is only effective against Japanese beetles, it won’t harm beneficial insects. It’s organic and extremely safe for use around children, pets and non-targeted species. It offers long-term, ongoing control, and only needs to be applied once per season. Follow the directions on the container for application, and then water the treated area to help the milky spore soak in and reach the grubs.
Don’t expect dramatic change after the first year of treatment; it can take up to three years to see a significant decline. I did notice a reduction after a couple of years, and even more each year since.
Beth Stetenfeld is an organic gardener, native plant enthusiast and garden blogger and writer. She’s also a master naturalist volunteer and instructor.
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