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Extension > Yard and Garden News > Dealing with Japanese beetles

Wednesday, July 5, 2017

Dealing with Japanese beetles

Jeffrey Hahn, Extension Entomologist

If you had problems last summer with Japanese beetles on your property, the odds are very good they will be pests again this year. In fact some people are already seeing them in high numbers. So the question is what can a gardener do?

Killing individual Japanese beetles is actually easy but the problem is what to do when there are a lot of them. There is no one guaranteed method for treating Japanese beetles. It is best to use as many different management steps as possible to improve your chances of keeping Japanese beetle feeding to tolerable levels.

Have you checked your garden recently for Japanese beetles?
  Photo: Jeff Hahn, University of Minnesota Extension
If you have a small garden, physical removal can be a good option, especially when only small numbers are present. However when Japanese beetles are numerous, it becomes impractical to handpick them every day. Another non-chemical option is to place a cheese-cloth, or similar type of fabric, around valued plants to exclude the beetles.

There are a few low impact insecticides available. Pyola is effective but this product is short-lived and repeat applications are necessary. Neem oil is also an option. It helps deter Japanese beetles but is less effective when large numbers are present. Both of these products can be toxic to pollinators so be sure to apply them when bees are not active.

Thinking of using traps to control Japanese
beetles? Save your money, they are not
effective.  Photo: Jeff Hahn, U of M Ext.
There are a variety of residual insecticides that you can use, like permethrin or carbaryl (Sevin). To protect bees, apply insecticides during late evening after bees are no longer active. The products should be dry by morning when bees become active again. If you are trying to protect a large tree, you may need to have it treated by a landscape or tree care company.

Deciding whether to treat trees and other plants will depend on how many of the leaves are still intact. If nearly all of them are already chewed up, then spraying does not help protect the plants. If there are still a lot unaffected leaves, then it is worth your while to treat them.

Keep in mind that trees that are healthy and mature are not going to be killed from just one year of feeding. Trees are quite resilient and can tolerate a lot of defoliation. If trees has been recently transplanted or are already under stress, it is a good idea to protect them from any additional damage.

What you don’t do is just as important as what you do try. Some people like the idea of using Japanese beetle traps to protect their plants. While these traps can capture an impressive number of beetles, the traps are attracting more beetles than they catch. Research has shown that when these traps are used in home gardens, damage is not reduced but in fact is likely to increase. Likewise, companion planting has been demonstrated to be ineffective in protecting plants from Japanese beetle feeding.

 For more information, see Japanese beetle management in Minnesota.

8 comments:

  1. after my Linden Tree was half eaten, I put up four traps. Withing two hours I had caught a good gallon of beetles. This continued for several days. In my opinion I may have saved my tree from being completely denuded like other nearby Lindens. Having disposed of nearly 4+ gallons of beetles my hope is there will be fewer eggs laid in my lawn and fewer grubs eating the grass roots. I plan to apply the grub chemical to my lawn and hopefully have fewer JB next year. I know all the authorities say this will not work but I feel it is better than doing nothing and letting another pest ruin the urban landscape. If this is allowed to continue unchecked then the future does not look good for our environment and a few dominant pests will rule and other species will not longer exist. You failed to mention that beside eating the leaves the JB also leaves and ugly residue of JB droppings on decks and sidewalks and premature shedding of damaged leaves. I believe I have done the proper action if only removing a large number of JB from the area surrounding my yard. If there are a million JB in the world there are now less thanks to my efforts.

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  2. i agree! i do think the traps help! i actually have found, after 4 years of battling these bugs, that placing the traps somewhat near my garden areas, not IN the flowers, but adjacent to them, draws the beetles to the traps...i am then able to more easily manage the ones venturing to my flowers by hand. i also use EIGHT. i bought some grub stuff from gardener's supply and applied it this spring--not sure if it helped. i will do it again next year. after investing a lot of time & money in all my flowers & landscaping, every effort is worth it to me!

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  3. I collect mine in a jar with soapy water everyday

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  4. I have to say, as I've travelled around the suburbs delivering packages for Amazon, I've seen several of the bags you picture above stuffed with these beetles. Teeming with them. In fact, I've never seen one that wasn't just crammed full.

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  5. The grapevine at the UM daycare has been decimated by these little jerks this year.

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  6. All of my apples, plums,grapes, hazelnuts and linden leaves have been skeletonized. I handpicked them everyday only to collect more and more. I tried neem oil and that didn't do anything except temporarily immobilizing them.
    I did set traps that seem to be doing the job.
    Wish there was a predator that preyed on these pestilent unrestrained revellers

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  7. as i read more & more about how insanely aggressive the invasion is this year, i feel pretty confident that my preventive action of using live nematodes (a grub prevention method) had SOME positive effect. i say this b/c this is my 4th year of battling this pest and this is the *mildest* year, for me!, that i've experienced. i will definitely do it again next spring! the product is from gardener's supply, out of vermont--can't remember the name of it, but just enter "grub" in search space...read reviews, as that did help me in the purchasing & application of the product. best of luck fellow earth mamas & papas!

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