Crabgrass

Characteristics

Crabgrass (Digitaria spp.) in Minnesota is primarily one of two species: large crabgrass (Digitaria sanguinalis), also known as hairy crabgrass, and smooth crabgrass (Digitaria ischaemum). Both species are annual warm-season members of the Poaceae family (grasses). You can tell them apart by the abundance of hairs on young crabgrass ligules (a membrane where the blade and sheaf meet) and leaf blades.

Typically growing between 1 inch and 3 feet high, crabgrass survives harsh conditions through its abundant tillering (creation of shoots other than the main shoot) and seed production. 

Flowers, fruit and seeds

• Seed germination time: early spring to late spring, when soil temperatures have an average temperature high enough to support growth.
• Seed reproductive time: summer to fall.
• Both Minnesota crabgrass species form seedhead racemes (spikes) between 2 and 6 inches long at the tips of stems.
• The branching structure of seedhead racemes combined with tillering allows up to 150,000 seeds per plant to be produced in a single season.

Leaves or blades

• Large crabgrass grows up to 3 feet tall, while smooth crabgrass typically only grows up to 1 foot. 
• Crabgrass contains a hairy ligule (collar-shaped growth) between the sheath and grass blade.
• Crabgrass blades are between 1 and 6 inches long and light green.
• Young large crabgrass blades have small hairs, although older leaves may become hairless.
• Smooth crabgrass may have some small hairs on the blades but will be primarily smooth.
• Older leaves and sheathes of both large and smooth crabgrass turn reddish-purple.
• Alternate growth.

Stem and roots

• Crabgrass stems form tillers (shoots other than the main shoot).
• Stems typically creep along the ground and can root at nodes.
  • Some people believe that the “crab” in crabgrass derives from the stems looking like crab legs.
• Crabgrass produces fibrous roots.

Where it thrives 

Crabgrass thrives in turf and landscapes with hot, dry, compacted soils. Crabgrass can outcompete many turfgrasses found in lawns due to its ability to thrive in intense heat and sunlight.

Crabgrass moves through stages of its life cycle according to day length. In the spring, once soil temperatures reach approximately 55 degrees, crabgrass seeds begin to germinate. The grass grows throughout the summer until days start to shorten and crabgrass enters its reproductive stage, forming seedheads.

Crabgrass drops its seed and dies by the first frost, returning in the spring. 

Control and management

Crabgrass can survive mowing due to its prostrate nature, allowing it to lie flat under mower blades.

Consider the crabgrass growth stage when hand-pulling and applying herbicides. 

Turf 

• Raise mowing heights to at least 3 inches to shade out the soil's surface. This will decrease seedling germination and emergence.
  • Crabgrass has poor shade tolerance.
• Change nitrogen application times to the fall.
  • Crabgrass is a warm-season grass that can outcompete cooler-season turfgrasses in the summer for nitrogen.
• Hand removal is effective for removing individual plants before seeding.
• A dense and healthy turf is the best defense against crabgrass encroachment.
  • Water turfgrass during drought to prevent dormancy and reduce openings for crabgrass.
• Apply a pre-emergent herbicide in the spring when soil temperatures reach approximately 55 degrees.
• Post-emergent herbicides are most effective on crabgrass seedlings before they produce side shoots.
• Pre-emergent herbicides:
  • Dithiopyr
  • Pendimethalin
  • Prodiamine
  • Benefin
  • Bensulide
• Post-emergent herbicides:
  • Dithiopyr
  • Mesotrione
  • Quinclorac
  • Topramezone

Garden

• Hand removal is effective for removing individual plants before seeding.

Benefits to the landscape

Large and smooth crabgrass have been used in grazing systems and hay production for farm animals. Crabgrass has also been grown as a cereal grain in many countries worldwide and throughout history.

Conservation, invasive status and native status

• Introduced.
• Crabgrass is native to parts of Europe and Asia and was brought to the United States as a forage crop in 1849. 

Plants that look similar

• Quackgrass
• Bermuda grass
• Tall fescue