Controlling Japanese Beetles in the Home Garden

In recent years, I have noticed increasingly larger populations of Japanese Beetles in my garden.  I first observed them in my garden a few years ago when I came upon them devouring my edamame soybean plants.  Easy to spot with their metallic green abdomen and bronze wings, I picked off as many as I could, but it seemed impossible to keep up with their numbers.  The following year, I found them devastating my sunflowers and zinnias. I have since learned that they will feed on over 300 species of plants, trees, shrubs, and grass, including common gardens plants such as sweet corn, sweet peppers, asparagus, soybeans, rhubarb, and more.

First reported in the United States in 1916 in Southern New Jersey, the Japanese Beetle, Popillia Japonica Newman, was accidentally imported here from Japan and quickly became a pest.  Without its natural predators, a hospitable climate and ample food supply made it easy for the Japanese Beetle to spread it’s population through most of the Eastern United States.  Efforts have been made to eradicate the beetle, but it has continued to thrive in the East, whereas Western and Southern states have prevented it from establishing through tough regulations and careful monitoring.  While it may be extremely difficult to exterminate them all together, it is possible for you to keep their populations in check and at a manageable level with the following strategies.

Hand Picking or Trapping

This was my original first line of defense in dealing with my own Japanese Beetle problem.  Hand picking is best done in the cool morning temperatures when they are more lethargic and dew on the beetle’s wings impairs their ability to fly.  They will often fall from the plant to escape your grip, so first place a light colored sheet (for better visibility) at the base of the plant and then gently shake the plant so that the bugs fall onto the sheet.  You can also pick them off the plant and dispose of them in a bucket of soapy water that you hold under the plant (to catch any strays as they fall).  There are also mechanical traps that are designed to attract and trap adult beetles.  These can be found at many lawn and garden centers, and should be used away from the main garden to lure the beetles away from your crops.  While hand picking and trapping is a benign way of controlling the adult beetle, this will not stop their life cycle.  Other measures must be taken to manage this beetle in its larval stage as well.

Biological Control

The adult Japanese Beetle is usually spotted in the garden from late spring through midsummer, while it is feeding and laying its eggs (which it does in burrowed holes in the soil).  Its’ young larva, the white grub, begins to hatch during midsummer.  This is a beneficial time to use biological controls to mange the beetle in its larval stage.  There several parasites, nematodes, and fungi that will target and kill these grubs, while at the same time leaving other potentially beneficial organisms unharmed.  Nematodes are microscopic parasitic roundworms that seek out the larva in the soil and inoculate the grub with a bacteria that feeds on the grub tissue.  The nematode then eats these bacteria, therefore establishing its own population and sustainably keeping the grub population down.  The most effective commercially available insect-eating nematode is called Heterorhabditis bacteriophora. Other biological controls are Bt, Bacillis thuringiensis which is an insect stomach poison and must be ingested by the grubs to kill them, and the bacterium Milky Spore, Bacillus popillae which infects the grubs with Milky Spore Disease and eventually perpetuates the disease in the soil to help keep the future of the population in check. Controlling Japanese Beetles with these biological methods takes longer than controlling with insecticides, but the results are much longer lasting.

Habitat Management

Trap Cropping, interplanting repellant plants, keeping your lawn and garden as healthy as possible, and choosing landscaping plants and trees that are not susceptible to the Japanese Beetle are also great ways to help control the populations.  Planting a trap crop of highly preferred varieties, such as pastel zinnias or marigolds, away from the main garden will help to lure the beetles to a tastier meal.  Remember though, trap crops serve to concentrate your pest population and lure them away from other, more valued crops; but the pest population on the trap crop still needs to be addressed through one of the control methods mentioned above – otherwise you are just serving to increase the overall population!

Interplanting repellant plants like garlic or chives with their strong odor, among your susceptible plants like soybeans will further help to deter them.  Remember also that insects are often attracted to diseased, undernourished, and injured plants.  Therefore, keeping your garden healthy and removing diseased or damaged plants can be beneficial insect control.

Lastly, think outside the box…or outside the garden in this case.  There are many trees, shrubs, and grasses that are highly susceptible to Japanese Beetles (and there are resistant ones as well).  Therefore if you plan to do any landscaping in the near future, keep in mind that introducing certain species, such as Japanese or Norway Maple, crabapple, and plum trees to name a few, are sure to increase the Japanese Beetle population in your yard and therefore bringing them closer to your garden.

Photos from http://www.ag.purdue.edu/

 

This entry was posted in Articles by Megen Hall, Plant Pests and tagged . Bookmark the permalink.

12 Responses to Controlling Japanese Beetles in the Home Garden

  1. Virginia Danielsen says:

    One organic method that was not mentioned was the use of chickens!! Japanese beetles are one of my chickens favorite food!!

  2. Jackie says:

    Any suggestions on those revolting squash bugs that are ruining crops?

  3. Eleanor says:

    This was very informative. I didn’t know anything about these pests. I have been very fortunate that I have never seen them in my garden. But I already use benneficil nematodes, Bt and milk spore in my garden. Also, the benneficial nematodes are great for controlling fleas (if you spray it on the lawn). I will be sure to watch for these bug in the future.

  4. judi says:

    i like to catch them in a yogurt cup with a few inches of water in it the pour that into our chickens water dish. when i yell ‘bug soup’ they come running.

    • Angel says:

      We also like to trap them in cups of water and then freeze them. It makes a refreshing treat for our chickens in the summer and some tasty treats for them in the winter months as well when bugs aren’t in supply.

  5. Bill says:

    We grew 3 types of pole beans this year on 4 pole bean towers. Interestingly, the Japanese Beetles have not touched the Green Romano Pole beans; the leaves are untouched and I never find a beetle on them! However, I pick them daily off the others – Kentucky Wonder and the Yellow Romano type. These pole bean towers are all in a row with the leaves touching one another, but for some reason the Japanese Beetles will not eat the leaves of the Green Romano bean. We will probably grow these exclusively next year because of that!

  6. gail says:

    This article is not very helpful to someone who’s been in the battle and not winning…. We grow for our farmstand and lose so much crop to these creatures, despite using all the mentioned methods. I’d like to know how do the “big boys” do it on commercial fields, ie High Mowing Seeds, et al?

    • High Mowing Organic Seeds says:

      Hi Gail,
      I will check in with our farm managers about this question – and see what solutions they have that are more geared towards commercial growers. – HMS

  7. High Mowing Organic Seeds says:

    A tip from one of our customers, “I have had success treating Japense beetles in my home garden,,, I use two approaches,,, 1 milky spore on my lawn,, 2 I put the beetles in a blender and spray whatever they are eating,,, it is amazin how they stop eating after you spray. The trick is to filter out the blended beetles as much as possible so that the liquid is mixed with water,(stockings work great for this),and sprayed onto the attacked plants,,,, I store it by freezing it as well,, and then BEFORE they start attacking i spray and it works pretty good,, Rain of course washes it off and u have to respray,,, this worked for slugs as well,,, so i highly suggest you get a blender at at yard sale,,, and not use,, your wifes,, (they get really mad) Jerry” Thanks, Jerry!

  8. Chris says:

    Three years ago I had moderately heavy beetle pressure – predominantly on my edamame. At that time I knocked the bugs off and sprayed with a vegetable oil/water emulsion which kept the beetles off the leaves until the oil wore off. It was a pain and messy and I worried about any beneficials that might have gotten sprayed. I also tried the garlic/chili pepper thing to no effect. The last two years the beetle pressure has dropped considerably for no particular reason I am aware of. I use no insecticides of any kind and never have. At this point, I do attribute my lack of severe insect predation issues to the fact that I simply let the ecosystem around me develop and so attract plenty of beneficials. I think this year I’ve seen about a dozen or so beetles all season. I have about three acres of which about an acre and a half are under cultivation with mixed vegetables.

  9. Dixie Townsend says:

    Does anyone know if neem oil works on Japanese beetles? I am a first time gardener and I do not have any experience with neem oil. Thanks!

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