I apply a pre-emergent crabgrass control in late April here in NJ.
It's been very effective. I usually have a few plants that emerge
anyway, but never any serious problem. If anyone is having problems, I
would check to make sure you're applying it correctly. You need to use
the correct amount and it needs to be applied just before temps get
high enough for germination. Best guide is when forsythias are
blooming, that's the time to apply it. Too late, it won't work because
they are already germinating. Too early, it will have diminished in
effectiveness long before it's needed. I see people applying it here
in March. No wonder it doesn't work!