Crabgrass is a weed almost everyone is familiar with. Two species are common in Virginia; Smooth crabgrass, Digitaria ischaemun, and Large crabgrass, Digitaria sanguinalis. As annuals, they germinate, set seed, and die within one year. As an annual weed, crabgrass spreads primarily by seed and doesn’t have rhizomes or stolons.
Crabgrass is easy to manage using a variety of cultural and chemical controls. Controlling crabgrass before it sets seed is important, because the seeds can remain viable for at least 3 years in soil. Because crabgrass spreads and reproduces primarily by seed, any cultural efforts that reduce seed production will decrease the potential of crabgrass invasion. These include using the proper mowing height, selecting the best turf species, overseeding to keep turfgrass thick, applying fertilizer at the correct time of year, and proper irrigation.
Irrigation timing and amount also can affect crabgrass germination and growth. Overwatered turf on turf that receives daily, light irrigation becomes weak and vulnerable to invasion by this grassy weed. Often, crabgrass first appears in open areas with no turf, along sidewalks where the soil can be warmer, or around areas where turf is mowed more closely.
Fertilizers can increase turfgrass vigor and reduce the possibility of a crabgrass invasion. The best time to fertilize is when the turf is actively growing, because seedling crabgrass isn’t very competitive, a vigorously growing turf will crowd out new seedling.