Crabgrass, sometimes called watergrass, is a warm-season annual grassy weed that is prevalent in Iowa. Crabgrass germinates in the spring once soil temperatures hit 55°F for four straight days and nights, and will die with the cooler weather and frost in the fall. Iowa has both Digitaria ischaemum (smooth crabgrass, smooth hairless stems with hairs where the stem and leaf meet) as well as Digitaria sanguinalis (large crabgrass, the stems and leaves contain hairs).