Japanese Beetle Control Fort Collins - Ask Extension
I live in Fort Collins and have been battling Japanese Beetles in my garden for the past few years. I would like to try beneficial nematodes, but nee...
Knowledgebase
Japanese Beetle Control Fort Collins #925799
Asked March 10, 2026, 4:41 PM EDT
I live in Fort Collins and have been battling Japanese Beetles in my garden for the past few years. I would like to try beneficial nematodes, but need some guidance on how and when to apply and what is the best variety?
Larimer County Colorado
Expert Response
Hi Sara,
I am assuming you want to use the nematodes to control the grubs in your lawn. It will be important for you to scout for the grubs/larvae before you use any nematodes.
They will only survive if they have grubs to feed on. It's hard to say if we'll have earlier insect appearances this year, based on the warm weather, but it's very possible. Typical Japanese beetles start to emerge sometime in July, so start scouting in June. Pull up sections of your turf and scout for any white grubs - they will feed on the turf roots below the thatch layer.
In terms of which species to purchase, look for the Heterohabditis nematodes (NemaSeek). These are "active" and they move around seeking and looking for prey. The Steinernema nematodes essentially wait for grubs to come to them.
What you'll want to do is scout for grubs in June and determine if there is a high enough population to treat. If so, then you'll make your first application. You can apply it to the turf areas with a watering can. Using a pump sprayer can also be used, but remove the screen, so it doesn't slice the nematodes. Your second treatment will be in July and the third will be in August.
Other tips:
•Purchase only fresh (check expiration date) product
•REFRIGERATE until use
•Store for no longer than 2 weeks in a refrigerator that is between 37° and 42° F
•Can be applied using a watering can, hose end sprayer, backpack or pump sprayer or through irrigation or misting systems
•Release early in the morning or pre-dusk when temperatures are cooler and the sun is not bright
•Water in well following application
If you wanted to control adults, you would use a Bacillus product (bacterium), such as BeetleGon or BeetleJus. But these are not nematodes.
I am assuming you want to use the nematodes to control the grubs in your lawn. It will be important for you to scout for the grubs/larvae before you use any nematodes.
They will only survive if they have grubs to feed on. It's hard to say if we'll have earlier insect appearances this year, based on the warm weather, but it's very possible. Typical Japanese beetles start to emerge sometime in July, so start scouting in June. Pull up sections of your turf and scout for any white grubs - they will feed on the turf roots below the thatch layer.
In terms of which species to purchase, look for the Heterohabditis nematodes (NemaSeek). These are "active" and they move around seeking and looking for prey. The Steinernema nematodes essentially wait for grubs to come to them.
What you'll want to do is scout for grubs in June and determine if there is a high enough population to treat. If so, then you'll make your first application. You can apply it to the turf areas with a watering can. Using a pump sprayer can also be used, but remove the screen, so it doesn't slice the nematodes. Your second treatment will be in July and the third will be in August.
Other tips:
•Purchase only fresh (check expiration date) product
•REFRIGERATE until use
•Store for no longer than 2 weeks in a refrigerator that is between 37° and 42° F
•Can be applied using a watering can, hose end sprayer, backpack or pump sprayer or through irrigation or misting systems
•Release early in the morning or pre-dusk when temperatures are cooler and the sun is not bright
•Water in well following application
If you wanted to control adults, you would use a Bacillus product (bacterium), such as BeetleGon or BeetleJus. But these are not nematodes.
