Where is Zone 4? Just in case someone from the South every reads this post, the first app of summer annual pre-emergent needs to go down in the Winter - not spring. By Feb. 15 in the Atlanta area.
Sounds like you already have crabgrass. Drive 75 works well, MSMA can work depending on the age of the weed and you will probably need multiple applications. Acclaim is another product labeled to control crabgrass but it has been falling out of favor for a while. If you want to prevent crabgrass, then dimension is a very popular choice. TEAM is another product that gets used a lot. I hope this info helps.
Barricade will also help as far as pre control. For post control there is a very easy step. As soon as the crabgrass appears simply dab a small amount of Roundup to the center of the crabgrass. You don't have to spray the entire plant. In a week or two the weed will be gone and you will have a dead spot that is the size of a quarter. If you are dealing with a turf that spreads like Bermuda then it will fill in the spot within a week or two. If you are dealing with a turf that doensn't spread like rye then simple re-seed the spot.
Acclaim will also kill existing crabgrass plants, providing that the growth is less than 5-7 tillers.
