Last June I had my lawn torn up and topsoiled and seeded. Needless to say all summer my lawn was loaded with crab grass. I managed to kill most of it, and now its March in NY and while all the crab grass seems dead id like to keep it that way. I can see the brownish areas that are dead crab grass. What do you guys suggest I do now to keep it from growing back? Should I throw some crab grass killer now, then grass seed in a few weeks? Please let me know your opinions?