Pests and Diseases: Japanese Beetles

Well, the Japanese beetles are zooming about and hiding out in your roses. They can quickly turn your prized plants into skeletons of their former selves. There are tons of chemicals that people use to kill them each year but is it really necessary? Do we really have to drench our beloved plants in insecticides to withstand the deluge of Japanese beetles? Let’s look at the life cycle of Japanese beetles to determine the best time to treat them.


japanese beetles
Photo courtesy of USDA


The winged insect that you see flying around in July is the culmination of a full year’s work. The eggs were layed in the soil the previous July or August and quickly hatched into grubs. Those tiny grubs eat plant roots until the temperatures cool down in the fall. At this point, they burrow down 4″-8″ to wait out the winter. In the spring as the temperatures rise, the larvae rise back to the surface where they mature into the adult that eats your plants. Now, thinking about how to successfully treat them, it only makes sense to treat the grubs when they are small in the late summer. In Virginia, August is the best time. If you wait until the spring, the grubs are large (over an 1″) and it takes much more chemical to kill them.

As you all know, I don’t like applying pesticides. As much as I don’t like them and won’t use them in my yard, I understand that many homeowners still prefer to use chemical methods. I would rather educate people so that if they apply chemicals they do so at the proper time instead of applying chemicals willy nilly. I am often asked in the spring what chemicals can be applied to take care of Japanese beetles. People are discouraged when I tell them that missed the boat and need to wait until late summer. At least you all know now.

In regards to more organic methods of Japanese beetle control there are a few options. The first is milky spore. It’s a soil dwelling bacteria that attacks the grubs and then reproduces in the soil. It is slow to establish itself but the magic of milky spore is that it continues to propagate itself without any effort from you. Another control option is trapping. There are the conventional yellow bag traps that have been used for decades and there are all sorts of newfangled ones. I saw an interesting video on a new type of trap that is renewable. I am by no means recommending it since I haven’t tried it but it’s still a great idea that I thought that I would pass along.

If you watched the video, you saw that backyard chickens are an integral part of the system. Chickens are a wonderful means of pest control that should be considered as part of any backyard garden. They provide pest control, manure that can be composted for your garden and “hen fruit”, the name that Joel Salatin has given to eggs.

Is your garden being inundated with Japanese beetles this year? What control methods are you using? Leave me a comment below or e-mail me to let me know. If you enjoy being part of the Mid-Atlantic Gardening community, join our e-mail list (upper right hand corner of this page), become a fan on Facebook and follow me on Twitter. Happy gardening!

July 10, 2012Permalink 9 Comments

9 thoughts on “Pests and Diseases: Japanese Beetles

  1. I’m interested in the milky spore but could use a little more coaching on the do’s and don’ts and how much?? Good piece and especially informative on when to address/apply.

    • Thanks Kenny. Here is a website for the product. I’m not personally recommending it since I’ve never had to treat for Japanese beetles (too much shade and not enough ornamentals that they desire).

      Also, realize that there have to be grubs for the milky spore to reproduce…sounds reasonable but as your grub population decreases over time, so will your milky spore population. But hey, what insecticide lasts for 10 years (in a good way)?

  2. Here’s a good blog post with a GREAT comment discussing milky spore.

    He says it affects scarab beetles…a group that includes dung beetles. I dunno. I wish the beetles would emerge long before my berries got ripe so I could save my berries with chickens rather than just pay the chickens to eat the berries and bugs at the same time.

    Looks like you just put a teaspoon down every 3-4 feet in a grid pattern.

    • Thanks for the blog link…I haven’t had a chance to check it out yet but I will. Did you check out the video in the original post? You could have these traps with your berries and then feed the girls the Japanese beetles. It’s pretty cool. Now I’m off to read up on these dung beetles that you’re so enamored with…

      • The video is pretty cool but I rotate my chickens across the farm. I guess you could put a bucket of soapy water under the trap when the chickens aren’t nearby. I think I like that method more than using milky spore. Plus, by attracting all the beetles from my neighbor’s farms I’ll be translocating nutrients in from outside…if I can trap them all.

  3. Pingback: Pests and Diseases: June BugsMid-Atlantic Gardening

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