Barbalee said:
Thanks, Kent! Yes, we get sub-freezing, but what I'm reading here tells me the roots will still be growing underground. Not so?? That's what this thread says, but I thought it would be gone after winter and I'd just have to be ready with pre-emergent. Now I'm totally not sure what to do! 
The plant in your picture is smooth crabgrass (Digitaria ischaemum) and it's an annual. It's growth really slows down
once nighttime temperatures start to dip below 50F, and one good frost will finish it off. Once it has been frost killed, you likely won't see it again until soil temperatures rise to around 60F next spring. Like I said above, the most efficient way to deal with it is to change how you mow and water your lawn, but there are a number of herbicides that people commonly use as well.
This link is from Illinois, but it contains good information for anyone dealing with crabgrass.
http://extension.illinois.edu/...
