Thanks very much for the information. Any idea how to determine where in the lawn the spores might be living? I have a pretty big lawn; wouldn't really know where to begin. Any signs to look for?

You spray the entire lawn :-) But you will often find browned, dead patches in spring from the root feeding of the grubs/larvae over winter and you can focus on those first.

One of the most efficient methods of control is hand picking. Tedious and time consuming and difficult on any shrub or tree of size but any reduction in numbers is a good thing. Also neem oil/azadirachtin sprayed on the foliage the beetles are feeding on can be very helpful.

I find them when I dig in my garden beds and lawn. I sometimes have had to reseed areas or take out big weeds, or transplant or dig out things. That's when I find the grubs. And that's how, after three years, I know the milky spore is working. Will not eliminate, but can greatly reduce. Also, important to properly fertilize and water your lawn. Over-fertilized lawns are ideal habitats for the grubs. I've changed that up since I moved into the house so don't have as many grubs.

Here's an excellent pamphlet on controlling the pests. It has a section on how to survey for the grubs. I never have surveyed since I run into them in my tasks throughout the yard. Plus I gauge my success by how many turn into adults . . . https://www.aphis.usda.gov/plant_health/plant_pest_info/jb/downloads/JBhandbook.pdf

Here's a great pamphlet that talks about how to water and fertilize the lawn properly to discourage the grubs. https://unis.mcgill.ca/en/uw/insects/beetle_grubs.html

I'm dealing with somewhere between one-and-a-half to two acres of lawn. I have an immediate front yard that borders the landscaping, but watering and fertilizing all the lawn on my property is unrealistic. So, there's no danger of my yard being over-watered/fertilized.

I feel your pain, I have a large lawn too. That makes milky spore an expensive option. Start with the area closest to your house and work outwards. We started with our front yard. This is a long term beetle management strategy. The pamphlets have some other ideas for a total plan, including planting resistant plants, and controlling and killing the adults. But you can get a handle on it. We did. We did the milky spore for three years and are now supplementing with a nematode treatment, same scenario, starting with the front lawn which is closest to our landscape plantings that we want to protect the most since they are the most vulnerable.