Hi - The best time to apply nematodes to control lawn grubs will be when the grubs are small and near the soil surface. For this area, that is typically around late June to early July. Heterorhabditis bacteriophora is a species of nematode that will control white grubs. You will have to read your product label instructions carefully regarding the method of application. The nematodes have a short shelf life and should be purchased just before application. They need good soil moisture to be effective. They also are sensitive to sunlight so you may need to apply the product in the evening or on an overcast day. Refer to the following pages for more information:

https://extension.umd.edu/hgic/topics/white-grub-management-lawns

http://ipm.ucanr.edu/TOOLS/TURF/PESTS/innem.html

https://www.maine.gov/dacf/php/gotpests/bugs/documents/nematodes-for-grub-control-maine.pdf

Christa