If you are in the deep South, south of Waco and to the east, NOW is the time to put down a preemergent for the early part of spring. I miss this date every year, but I think I have a handle on it now. Most preem's work for 3 months. Applying in mid to late January will hold you through the grass awakening month of March and into April. In mid April, assuming you have some weeds that sprouted last fall, you can spot spray those with Weed-b-Gon (for bermuda) or atrazine (for St Augustine).

I'm tempted to change this date to January 1st for the Deep South. I'm watching weeds this spring.