Japanese Beetles - Ask Extension
We have Japanese beetles. So far as we can tell, they have been attacking our roses and potentilla. We applied a grub retardant in early spring, but h...
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Japanese Beetles #880377
Asked August 06, 2024, 11:20 AM EDT
We have Japanese beetles. So far as we can tell, they have been attacking our roses and potentilla. We applied a grub retardant in early spring, but have primarily just been picking the beetles off of the plants. We have read conflicting articles about how to deal with them. One article talked about traps. We’ve ordered them but haven’t used them yet because another article said using the traps would attract more beetles to our yard. Also, how does one get a neighborhood involved to combat this pest? Finally, we have a beautiful Norwegian maple in our front yard and we understand that these beetles may attack it, also. Any advice will be welcome.
Weld County Colorado
Expert Response
Carol,
Thank you for your question. And, thank you for your patience.
Control in Lawns: Controlling Japanese beetle grubs in the lawn is one way to decrease the numbers of Japanese beetles coming out of your lawn. This article gives information on biological and chemicals to choose and the critical timing for application to the lawn. Per article, GrubEx has long persistence and low toxicity to pollinators, people and pets. It should be applied in May/June. Follow directions on the label exactly when using.
https://extension.colostate.edu/topic-areas/insects/japanese-beetle-5-601/
Traps: Per the above article, CSU does not recommend using traps. "...the use of Japanese beetle traps often increases damage by Japanese beetles by drawing into the vicinity larger numbers of beetles than are captured in the traps. Because of this Japanese beetle traps are not recommended for Japanese beetle control".
Control on Plants: Frequent hand picking is a very effective approach to control beetles on specific plants like roses. Daily attention can control damage to foliage and flowers.
Insecticides can be used but care should be taken related to toxicity for pollinators. A spray has been developed (sold as beetleGONE! or beetleJUS!) that is a stomach poison for Japanese beetles when they eat sprayed vegetation but low toxicity for pollinators. See above article for both biological and chemical applications. Follow directions on the label exactly when applying.
Norwegian Maple: Norway maple is one of the trees that Japanese beetles do like. If you are seeing beetles on the tree and it is small enough, hand picking can be done. If this is a mature tree, consult a tree service professional for advice on treatment. I have also posed this question to a CMG colleague who is a tree specialist and if I get any other useful information, I will send it to you.
Neighborhood Participation: If you live in an HOA, you could consider appealing to your Board for action. Also contacting your city government for assistance.
Hope this helps. Please let us know if you have any other questions.
Ruth, Weld County Colorado Master Gardener
Thank you for your question. And, thank you for your patience.
Control in Lawns: Controlling Japanese beetle grubs in the lawn is one way to decrease the numbers of Japanese beetles coming out of your lawn. This article gives information on biological and chemicals to choose and the critical timing for application to the lawn. Per article, GrubEx has long persistence and low toxicity to pollinators, people and pets. It should be applied in May/June. Follow directions on the label exactly when using.
https://extension.colostate.edu/topic-areas/insects/japanese-beetle-5-601/
Traps: Per the above article, CSU does not recommend using traps. "...the use of Japanese beetle traps often increases damage by Japanese beetles by drawing into the vicinity larger numbers of beetles than are captured in the traps. Because of this Japanese beetle traps are not recommended for Japanese beetle control".
Control on Plants: Frequent hand picking is a very effective approach to control beetles on specific plants like roses. Daily attention can control damage to foliage and flowers.
Insecticides can be used but care should be taken related to toxicity for pollinators. A spray has been developed (sold as beetleGONE! or beetleJUS!) that is a stomach poison for Japanese beetles when they eat sprayed vegetation but low toxicity for pollinators. See above article for both biological and chemical applications. Follow directions on the label exactly when applying.
Norwegian Maple: Norway maple is one of the trees that Japanese beetles do like. If you are seeing beetles on the tree and it is small enough, hand picking can be done. If this is a mature tree, consult a tree service professional for advice on treatment. I have also posed this question to a CMG colleague who is a tree specialist and if I get any other useful information, I will send it to you.
Neighborhood Participation: If you live in an HOA, you could consider appealing to your Board for action. Also contacting your city government for assistance.
Hope this helps. Please let us know if you have any other questions.
Ruth, Weld County Colorado Master Gardener
