Crabgrass is a summer annual that germinates when soil temperatures reach a consistent 55 degrees F and is generally killed at the first frost. Crabgrass leaves are rolled in the bud; the first leaf appears short, wide and blunt-tipped. The ligule is tall and membranous with jagged edges, and the auricles are absent.
Do not seed, core aerate or verticut when soil and weather conditions are appropriate for the germination of crabgrass. A slightly raised mowing height may help prevent the establishment of crabgrass by providing shade from sunlight. When crabgrass is going to seed, lower the mowing height and collect clippings to prevent seed establishment.
Source: Virginia Polytechnic Institute & State University