How To Kill Japanese Beetles

My War With An Unrelenting Insect

About three years ago I had my first encounter with Japanese Beetles. The encounter happened to be death and destruction of a massive portion of my, at the time, small garden. The newly planted apple trees and rose bushes got the brunt of their assault. Everything had at least some damage by these insects. They land on the leaves and flowers of my plants and eat like cows until the plant is unrecognizable. I looked on in horror as my once prolific plants were mangled and turned into swiss cheese. Think Charlie Brown Christmas tree… OK, maybe not that bad. But they had declared war and I decided to try everything I could to get rid of them.

Today I’ll go over a few options available to combat these insects and my recommendations and experiences with each. But first, let’s cover what Japanese Beetles are for those of you who have never seen or heard them.

Japanese beetles are really an interesting insect. They are a decent sized beetle, I would say the size of a marble. Not nearly as big as a June Beetle (nor as crunchy, gross). They have brownish wings with metallic green accents around the rest of their body. Very identifiable; you will know one when you see one. Japanese beetles are not native to North America and in fact are not as much of an issue in their native habitat. The reason for this is that there is very few predators located here to keep their populations in check. In Wisconsin, they tend to begin to arrive the first weekend in July. Almost on queue you will begin to see them landing on your favorite plants and eating them. The list of plants they like, unfortunately for us, is a very long one. And so we are left to our own devices to defend our fragile roses and raspberry bushes from the invading swarm.

So how do we get rid of the? Let’s talk about six options for killing Japanese Beetles.

  1. Milky Spore

One way to kill the beetles is to get them while they are still larvae, before they hatch into beetle form. At most big garden stores they will sell a product called “Milky Spore” which you can apply to your lawn and let it grow. Essentially, it is bacteria that will latch onto and kill the beetle larvae. It may take a year or so in order for the spore to grow numerous enough to have an impact, but that is not the only issue. I have not used this on my lawn because for one it is pretty expensive for those who have a decent area to apply this too. Secondly, if you apply this to your lawn, but your neighbors do not apply it to theirs, the beetles will just hatch in the lawn that is not infected and fly right back over to your plants upon reaching adulthood. Therefore, I would not start with this tactic.

  1. Traps

Something I have personally tried, but do not recommend. Japanese beetle traps are generally hung on a shepherd’s hook or somehow off of the ground. They are a green tube with one end closed and the other with yellow fins that prevent the beetles from getting out. Inside, you place an attractant that brings them in by the droves. Two years ago, I used two of these traps and killed a few thousand beetles. You would think that my neighborhood would be clear of beetles after that many, but in fact I think it actually brought in more beetles then I would have normally had. Thousands were killed, but thousands were not, and they laid their eggs in my yard. If you use these traps, expect more beetles than normal.

  1. Sprays

You could give sprays a try. I have used “Sevin”, soap and water mixture, and “Neem Oil” to kill/ward off the beetles. Personally, they haven’t produced great results. Both the “Sevin” and soap/water mixture seemed to do more harm to the plants then the beetles in my case. The other thing is, once it rains, you need to respray. “Neem Oil” is part of a mixture I use on my fruit trees regularly, so they get sprayed with this normally. “Neem Oil” coats the leaves so that when an insect begins eating them, it induces vomiting and the insect leaves it alone. It seems to keep some of the numbers down, but do not expect it to eradicate the beetles. If you want to spray, I suggest mixing “Neem Oil” with water and doing a few applications to your favorite plants.

  1. Soapy Water**

This is my main method of attack nowadays. It is the second prong in a two prong approach that I take with Japanese Beetles. Take a bucket of soapy water with you as you tour your garden, and whenever you see a beetle, grab it and put it in the bucket. Now there are a couple tricks to this. One, the beetles like to let go of the plant when you get close and roll to the ground to escape. Cup your hand under the leaf and let them roll right in. Secondly, the best time to do this is in the morning. Japanese beetles are super slow when it is cold out and morning is best. If you try this in the afternoon when it is hot, they are active and fast. You will miss more than you will catch. Highly effective, but manually intensive.

  1. Geranium

Probably the most unique weapon on the list is geranium plants. There have been some studies that show that Japanese Beetles that eat geranium leaves become paralyzed for a period of time. Combine this paralyzation with the heat of the sun and you have a cooked beetle. I placed one of these by my traps the year I used them and had dead beetles in the trap and a pile of dead beetles beneath the geranium. Place these around the plants that are most affected and you may have some added protection. I will say that they do not actively search out geranium, so this may not be as effective as you hope.

  1. Nature**

This is now the second prong in my two prong attack. Ever since I have been trying to heal my yard and the land around it, I have increased the numbers of beneficial insects and birds twofold. Birds, especially crows and sparrows, will eat the beetle larvae before they hatch. I’ve also noticed an increase in parasitic wasps in my yard which lay their eggs on beetle larvae that will consume and kill the beetle before it hatches as well. Skunks too, will dig up beetle larvae and eat it. Although I don’t think you want skunks in your yard. All of this wildlife has really reduced the beetle numbers in my yard to make using the soapy water method the only other thing I need.  

In general, I’ve found that conventional means of fighting Japanese Beetles to be more harmful than good. Either they bring in more of the bad guys, or they hurt the plants I’m trying to protect. Using natural organic and permaculture methods, described in this blog, to promote beneficial insects and birds, has been the best tactic for my garden. Nature has a way of balancing itself out. All you have to do then is take care of the leftovers.

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About the Author

Geoff has been growing plants and vegetables consistently for the last 6 years and actively experiments with, and writes about, all aspects of gardening.

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