For the last couple weeks, Japanese beetles have been making their seasonal appearance, and now they have crashed our party in vast numbers. Boldly strutting into our gardens like they own the place, rudely eating what is not meant for them, and offensively humping on every available surface. It’s like an 80′s coke party except these assholes are stone-cold sober.
The Japanese beetles are an invasive species, and are very capable of destroying many different types of plants. In my gardens they are particular to my grape vine and my soybeans. The beetles start out as grubs that hatch from eggs below the soil surface.
There are a number of things you can do to limit the populations. I am personally against the use of insecticides for the adult beetles that can also harm other insects (not to mention my food), so taking that into account, here is my list, in order of my most preferred, to least preferred:
List for Japanese Beetle Destruction
1. A bucket of soapy water, and knock the beetles in.
I hate to get all high-tech on you, but the beetles are generally slow to take flight, and in a typical home garden a daily (or every-few-days if you’re like me) walk through will be enough to avoid catastrophe. I keep my bucket of water perpetually on the porch so that I can just grab it quickly when I’m walking by. This was my sole approach last year and was happy with the results. This year I’ve noticed some of the beetles are more willing and able to fly away. Has anyone else noticed this?
2. Parasitic Nematodes.
There are species of nematodes that feed on the grubs. Locally, I’ve known Bachman’s to have nematodes in stock, and suppliers on Amazon.com have nematodes, as well. You apply the nematodes to the soil at night, and then keep the soil moist to keep them alive. Keep in mind you’ll just be reducing the grubs in your yard, and some beetles can (and will) fly in from elsewhere.
3. Plant geraniums!
Geranium flowers can be deadly to the Japanese beetle. A particular amino acid in a geranium flower that causes paralysis of the Japanese beetle is identified in this study, and you can watch the paralysis here. This blogger has had success controlling Japanese beetles with geraniums.
4. Pheromone traps.
Pheromone traps use scents to attract Japanese beetles from surrounding areas, at which point you drown them as in #1, or kill them some other way. There is much disagreement about this approach, because it does seem that the trap attracts more beetles to your area without being able to trap all of them. However, I am of the opinion that I’d rather attract them from a neighbor who chooses not to control their populations and just control the population myself. This is an example pheromone trap on Amazon.com: Japanese Beetle Trap.
5. Milky Spore Disease.
This is a bacteria that you can introduce to the soil that does not affect beneficial insects, but causes disease in the Japanese beetle grubs. I just saw some at my Ace Hardware store. The U of M Extension and at least one entomologist at Ohio State says that recent trials show milky spore has not been particularly effective.