My soil here in VA @4 inches was 50 degrees on Monday. I think we will hit 55 by Friday which is the magic number for crabgrass preventer. I think you probably have another week or two after that (at least) if you are in Wisconsin.

It is always better to get it early than late though. I would wait longer though up your way.

The people at your local office of your University of Wisconsin Cooperative Extension Service would be better able to answer that then someone from far distant places that do not know your local conditions. What MSU CES has told us for many years is to apply Crab Grass preventer when the Forsythia are in bloom.

Or better yet, get a soil thermometer and apply when it hits 55 @ 4 inches!