Japanese beetle - Ask Extension
We live just south of your office on Greenbriar Park. We have almost an infestation of Japanese beetles, first time I’ve seen them in 20 years here....
Knowledgebase
Japanese beetle #878457
Asked July 23, 2024, 3:44 PM EDT
We live just south of your office on Greenbriar Park. We have almost an infestation of Japanese beetles, first time I’ve seen them in 20 years here. They are devouring a young peach tree, cinquefoil and garden green bean leaves at the moment. We bought two Bag a Bug Japanese beetle traps and probably got 400+ in 2-3 days. However, we just threw out the traps because we still had bugs on the plants (perhaps fewer) and wondered if we were actually attracted all the neighbors beetles too. We’re still hand picking them off and killing in soapy water. We are putting in an entire new xeriscape yard this week with many new plants. We’re worried about the beetles eating them.
All this to say- do you know how long this infestation will last, life span of this bug, etc?
Thanks for any help, Megan
Larimer County Colorado
Expert Response
Hi Megan,
You are correct that beetle traps attract beetles - and are best not used. Japanese beetles have been in Fort Collins for several years and are slowly spreading. They are here to stay, so finding tolerance for their damage and doing what you can and using the options available are good solutions.
Handpicking can be VERY effective. The beetles are around for a few weeks, and picking them every morning when it's cool and less sunny is a great way to help control populations.
There are also things you can use to spray on your most desirable plants, such as BeetleGon and BeetleJus. These products stop the beetles from feeding, but it take several days for them to die. You will need to apply these every few days because they break down in UV light.
Milky spore will not work, so skip that. I would suggest you watch the webinar our state Extension entomologist did a couple years ago about the insect and the control options available. You can watch here.
Because this insect has been in the U.S. for over a century, there are very good biological controls available. As for your new xeriscape garden, these plants may not be as attractive to the beetles. My colleague in Douglas County has been monitoring plants that are attractive to JB. You can find more details here: https://douglas.extension.colostate.edu/horticulture/publications-2/
You are correct that beetle traps attract beetles - and are best not used. Japanese beetles have been in Fort Collins for several years and are slowly spreading. They are here to stay, so finding tolerance for their damage and doing what you can and using the options available are good solutions.
Handpicking can be VERY effective. The beetles are around for a few weeks, and picking them every morning when it's cool and less sunny is a great way to help control populations.
There are also things you can use to spray on your most desirable plants, such as BeetleGon and BeetleJus. These products stop the beetles from feeding, but it take several days for them to die. You will need to apply these every few days because they break down in UV light.
Milky spore will not work, so skip that. I would suggest you watch the webinar our state Extension entomologist did a couple years ago about the insect and the control options available. You can watch here.
Because this insect has been in the U.S. for over a century, there are very good biological controls available. As for your new xeriscape garden, these plants may not be as attractive to the beetles. My colleague in Douglas County has been monitoring plants that are attractive to JB. You can find more details here: https://douglas.extension.colostate.edu/horticulture/publications-2/
Thank you very much for this thorough information. It’s timely and much appreciated.
Megan
On Jul 23, 2024, at 2:31 PM, Ask Extension <<personal data hidden>> wrote:
