Japanese beetles?? - Ask Extension
Hello,
Is there anything that can be done about the Japanese beetles? Preferably organic... Last late summer/fall I put down Milky Spore, but they ...
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Japanese beetles?? #865352
Asked April 21, 2024, 8:12 PM EDT
Hello,
Is there anything that can be done about the Japanese beetles? Preferably organic... Last late summer/fall I put down Milky Spore, but they came back worse than ever. I can tolerate a little bit of munching, but they're defoliating even my salvias at this point.
Thanks,
Laura
Hamilton County Ohio
Expert Response
Hi Laura,
Japanese beetles are really challenging! In part, this is because there are so many types of plants that they are willing to eat, and in part it is because both larvae (grubs) and adults do damage in different ways and in different places. Since you mention defoliation, I am guessing that you are noticing the Japanese beetles' effect mostly from the adults skeletonizing leaves on your plants. Let's first consider how they got there.
Do you have patches in your lawn - areas with dead grass, especially spongy areas that are dead and/or animals are digging there? This often indicates the presence of the larval stages of Japanese beetles, which are white grubs that live in the soil and eat from plant roots. Those progress through the stages of the life cycle to become adult Japanese beetles. We have a fact sheet that describes this life cycle, and issues with all life stages, at https://ohioline.osu.edu/factsheet/ENT-46.
If these insects are hatching and developing on your property, one way to reduce populations is to treat for the grubs and kill them before they become adults. However, Japanese beetles can travel fairly far from where they develop, so the adults that are eating your plants may be overwintering and maturing somewhere else, and then arriving to eat your plants as adults.
It is very difficult to organically treat for adult Japanese beetles. There are some treatments that have been approved for organic use (see this link https://ipm.missouri.edu/MEG/2018/1/organic_management_japanese_beetle/), but chemicals approved for "organic" use because they are not harmful to humans can still be just as deadly for native pollinators as they are for Japanese beetles. Also, if Milky Spore did not work for you, it may be because it was not applied at a time when the grubs were eating, or it may be that the adults flew in from another location in your area.
There are a few other options that you may not have tried yet. You can check out the Homeowner's Handbook for managing Japanese beetles from Missouri Extension at this link:
https://extension.missouri.edu/media/wysiwyg/Extensiondata/CountyPages/Butler/JapaneseBeetleHandbook.pdf.
Be very wary of trapping adult Japanese beetles. In residential landscapes, trapping can often attract way more beetles than would otherwise have been there and actually increase plant damage. Although you are not farming, there are some very good ideas for control of Japanese beetles in this article for farmers: https://www.canr.msu.edu/news/managing_japanese_beetles_in_fruit_crops.
I hope this information is helpful, and please don't hesitate to contact us again with any further questions.
Best,
Japanese beetles are really challenging! In part, this is because there are so many types of plants that they are willing to eat, and in part it is because both larvae (grubs) and adults do damage in different ways and in different places. Since you mention defoliation, I am guessing that you are noticing the Japanese beetles' effect mostly from the adults skeletonizing leaves on your plants. Let's first consider how they got there.
Do you have patches in your lawn - areas with dead grass, especially spongy areas that are dead and/or animals are digging there? This often indicates the presence of the larval stages of Japanese beetles, which are white grubs that live in the soil and eat from plant roots. Those progress through the stages of the life cycle to become adult Japanese beetles. We have a fact sheet that describes this life cycle, and issues with all life stages, at https://ohioline.osu.edu/factsheet/ENT-46.
If these insects are hatching and developing on your property, one way to reduce populations is to treat for the grubs and kill them before they become adults. However, Japanese beetles can travel fairly far from where they develop, so the adults that are eating your plants may be overwintering and maturing somewhere else, and then arriving to eat your plants as adults.
It is very difficult to organically treat for adult Japanese beetles. There are some treatments that have been approved for organic use (see this link https://ipm.missouri.edu/MEG/2018/1/organic_management_japanese_beetle/), but chemicals approved for "organic" use because they are not harmful to humans can still be just as deadly for native pollinators as they are for Japanese beetles. Also, if Milky Spore did not work for you, it may be because it was not applied at a time when the grubs were eating, or it may be that the adults flew in from another location in your area.
There are a few other options that you may not have tried yet. You can check out the Homeowner's Handbook for managing Japanese beetles from Missouri Extension at this link:
https://extension.missouri.edu/media/wysiwyg/Extensiondata/CountyPages/Butler/JapaneseBeetleHandbook.pdf.
Be very wary of trapping adult Japanese beetles. In residential landscapes, trapping can often attract way more beetles than would otherwise have been there and actually increase plant damage. Although you are not farming, there are some very good ideas for control of Japanese beetles in this article for farmers: https://www.canr.msu.edu/news/managing_japanese_beetles_in_fruit_crops.
I hope this information is helpful, and please don't hesitate to contact us again with any further questions.
Best,
