Japanese Beetles: A List For Destruction

Japanese beetles in the process of decimating my soybeans. They must be stopped.

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.

My bucket o’ death.

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.

11 responses to this post.

  1. Posted by Smile4Ang on 07.21.2012 at 11:54 pm

    we carry a ziplock bag and pick the beetles, and baggie them, than crush and trash in a sealed bag. Brutal yet effective!


    • I like that idea. Then you can use the end of the bag to herd them in! (I am grossed out by touching them) :)


  2. Posted by Erica on 07.11.2012 at 3:34 pm

    Hey, I know the first author on the geranium study. You should understand that by “making a tea” out of geranium leaves, you’re essentially creating a pesticide. Sure, it’s not going to be of the same caliber as if an organic chemist extracted the compound. Many insecticides are derived from plants. It looks like this pesticide has a familiar mode of action as well. The reason it paralyzes is because it binds to same receptor as a neurotransmitter, over exciting the neuromuscular junction until death occurs.


    • That’s awesome you know the author! :) I understand that a tea would be a “pesticide” in the broad definition of the word, but to me it seems about equivalent to how a geranium flower could theoretically be considered a pesticide when purposefully planted near a grape vine. As you said, there’s a significant difference in degree.


  3. Posted by stephanie k on 07.11.2012 at 2:23 pm

    I need to find some quisqualic acid spray (geranium magic)!


    • I wonder if you made a “tea” with your geranium flower heads, and put it in the spray bottle, if that would work…? You should try it and let me know!


  4. Posted by Lydia on 07.11.2012 at 2:19 pm

    They have been chewing down my geraniums. However, I did find a number of them laying dead around the pot. Hmmm. I think I’ll go get more geraniums. The bucket approach has worked well and I was wondering if we’re selectively kill off the slow movers and will have a new super breed of fliers. Yes, a lot of fliers the past week or so.


    • That’s what I’m afraid of, too…by all of us using the bucket method we’re selectively breeding them to fly away. Scary!


      • Posted by Erica on 07.11.2012 at 4:07 pm

        The escape response for many beetle species is to simply drop off the plant rather than to fly away. You’re probably ok, unless this is a concentrated effort used across the board they likely won’t evolve a behavioral counter response, as some beetles have to crop rotation.

      • Hm…I *do* think that this is the method used across the board, at least by home gardeners. How widespread do you think it has to be to trigger an evolved response? All I know is that last year I didn’t see a single beetle fly away, and this year probably a quarter of them attempt to fly away, so it kinda seems like a big difference.

      • Posted by Erica on 07.14.2012 at 8:28 pm

        It took many years of farmers rotating between corn and soybeans for the corn rootworm beetle to evolve extended diapause/oviposition in soybeans. A year just seems really fast to me. You wouldn’t even see insecticide resistance evolving that quickly, and that’s usually a single gene. I’m used to this species flying away when I try to catch them – they seem like good fliers in comparison to other scarabs. You’re probably ok continuing to use the bucket method.

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