Thanks for your question.

Beneficial nematodes are microscopic, soil-dwelling roundworms that can be a powerful organic tool in controlling lawn and garden pests—especially grubs (larval stage of beetles like Japanese beetles, June bugs, and European chafers). A commonly used nematode species is Heterorhabditis bacteriophora. These nematodes enter the grub’s body through natural openings and release bacteria that kill the grub within 24–72 hours. After the grub dies, the nematodes reproduce inside it, and new nematodes emerge to seek other hosts.

The most effective time in Minnesota to apply them is late July and into August. This is when grubs are young and close to the soil surface. In using them, one also needs to monitor the soil temperature as it should be above 50°F.

As Extension Master Gardeners of the University of Minnesota, we cannot recommend specific commercial vendors. However, if you do a web search for “grubs, beneficial nematodes, Minnesota”, you will find many locations listed as sources. Usually, one obtains them from an online source who ships them to your residence.  Application procedures will differ from source to source. Always follow the instructions that are provided you with the nematodes you receive. Generally, the soil is watered prior to introducing them. This introduction procedure may involve a watering can, a hose-end sprayer, or a pump sprayer. It is usually done during the cooler parts of the day (mornings, evenings). The area being treated must be kept moist for approximately 10 days afterwards. Sometimes a second, even a third, treatment may be necessary. If you use them, you will find that it is a more expensive option than GrubEx. If you anticipate going down this route, it will take some prepping and planning time in advance. Once these nematodes appear on your doorstep, you will need to get them into the ground ASAP.

Another point to keep in mind is that applying beneficial nematodes is NOT a permanent solution. Like GrubEx, you would need to obtain new nematodes on an annual basis.

See the following for further information on these and related points:

https://ncipmhort.cfans.umn.edu/sites/ncipmhort.cfans.umn.edu/files/2021-10/2011 Krischik Japanese-Beetle-Management-in-Minnesota.pdf

https://www.ecolandscaping.org/05/landscape-challenges/pest-management/controlling-grubs-milky-spore-disease-or-beneficial-nematodes/

https://cals.cornell.edu/integrated-pest-management/outreach-education/fact-sheets/heterorhabditis-bacteriophora-beneficial-hb-nematode

https://extension.umd.edu/resource/beneficial-nematodes/

Good luck with your battle against grubs. Thanks for consulting us.