Thanks for the question.

Although you did not specify, I assume that you are looking for a way to eliminate white grubs from your yard. White grubs are immature forms of various beetles. In Minnesota and especially in the Metro Area, the two most common are June Bug Beetle grubs and Japanese Beetle grubs. For some background information on these, see:

https://extension.umn.edu/news/white-grub-control-lawns

https://extension.umn.edu/yard-and-garden-insects/japanese-beetles

http://cues.cfans.umn.edu/old/extpubs/7664japanese/DG7664.html

The effectiveness of beneficial nematodes in controlling white grubs is very time-sensitive. They are most effective when the grubs are in their active feeding stage, which is usually during the spring and fall months. In Minnesota, this would generally mean applying beneficial nematodes in late spring to early summer (May to June) and again in late summer to early fall (August to September). These times coincide with when grubs are most vulnerable and actively feeding on roots.

However, it's also essential to monitor soil temperatures, as beneficial nematodes are most effective when the soil temperature is between 60°F and 90°F (15°C to 32°C). Therefore, it's crucial to time the application when soil temperatures are within this range for the best results. You may find the following to be helpful in determining the soil temperature in your area:

https://gis.mda.state.mn.us/mda-soiltemp/

There seems to be mixed results with respect to the use of beneficial nematodes to control white grubs in Minnesota. In some instances success has been recorded whereas in other cases, they seem to have been ineffective. In general, their effectiveness can vary depending on factors such as the species of nematode used, environmental conditions, and application methods. It's important to follow the recommended guidelines for application and choose the right nematode species for the specific type of white grub infestation. As previously described, timing of application is crucial and is typically done in the late summer or early fall when white grub larvae are actively feeding near the soil surface.

As volunteer Master Gardeners of the University of Minnesota and to maintain impartiality, it is our policy not to recommend specific commercial products or vendors. We trust that you will understand this.  However having said this, if you do a Goggle search on "beneficial nematodes AND vendors", you will find several different sources.

Good luck. Please get back to us if you have additional questions.

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