Dallis grass is native to Central and South America and has been naturalized to the United States as a livestock feed crop. It is used as a cover crop for erosion control in many parts of the world, but is also considered an invasive weed in lawns. Crabgrass was introduced to the U.S. in 1849 as a forage crop. Both types of grass form flower and seed clusters in the fall for spring germination.
Dallis grass (Paspalum dilatatum), also known as water grass, is a warm-season perennial plant that easily invades turf lawn areas. It grows in clumps with coarse-textured leaves that grow from rhizomes and produce seed stalks 1 to 3 feet tall. The leaf blades are flat, hairless and spiked, and become red-tinged with age. It reproduces by seed and rhizome spread.
Crabgrass is an annual plant that grows as a perennial in temperate climates. It has yellowish-green leaves that are conspicuous in a finely textured turf lawn. Crabgrass is also known as hairy crabgrass, finger grass, crow foot, purple crabgrass and Polish millet. Crabgrass spreads on lateral branches known as tillers and by prolific seed germination. One plant produces from 150 to 700 tillers and up to 150,000 seeds.
Dallis grass is perennial in all climates. Plants flower, seed and begin the reproduction phase in the fall. Rhizome spread occurs throughout the life of dallis grass. Flowering begins in spring and continues until fall, with little foliage produced over winter. Crabgrass spreads by tillers and seed, which drop in the fall and germinates in spring.
Crabgrass seed germination is related to soil temperature, which must be above 60 degrees F for a week or more. Seeds are dormant for short period as they are shed. As the days shorten in fall, crabgrass slows its growth and goes into its reproductive cycle. Purplish seed heads form until frost kills the plant, emerging again in spring. Dallies grass ripens progressively over summer until fall. When dallis grass is produced as a feed hay it is harvested in the fall.
Crabgrass and dallis grass are considered invasive weeds in finely textured turf grass, such as fescue. In small areas, crabgrass can be controlled by hand picking. Corn gluten meal is an organic pre-emergent herbicide used for crabgrass control--it prevents seed germination but does not affect growing plants. Dallis grass can be controlled by hand picking or using a mulch cover, such as newspaper or black plastic.