I've been working in this industry for 20 years. If you live in the northeast, it's not crabgrass. Crabgrass (at least in the northeast) is an annual grass that generally comes up between June-late August depending on weather conditions. The best way to prevent crabgrass is to block it from coming up. Put down a pre emergent for crabgrass in the spring, I'd actually do this twice about 6 weeks apart. Mow your grass tall all season (I mow my lawn at a minimum 4 inches) and start to water BEFORE your lawn becomes stressed and dried out. Crabgrass is one of the hardest weeds/grasses to control, especially once it's fully mature, but it is an annual grass so it doesnt last forever. Generally once Temps get down in the 30s, the crabgrass dies for the season.