crabgrass

Large crabgrass (Digitaria sanguinalis) Photo: Betty Marose

Updated: June 29, 2021

Life cycle

Large crabgrass (Digitaria sanguinalis) is a summer annual weed. It is also called hairy crabgrass.

Growth habit

Crabgrass has a prostrate growth habit; the lower stems branch out and spread across the ground, and it can grow upward to 2 feet tall. The stems have swollen nodes; plants can develop roots at the nodes and form small colonies. The leaf blades have small hairs. Roots are fibrous. Flowers have 3 to 5 or more spikes. Crabgrass dies after the first frost in the fall.

Reproduction

Crabgrass reproduces primarily by seeds, which germinate from spring through late summer when the soil temperature is above 55°F for at least 3 consecutive days.

Conditions that favor growth

Thin turf with bare spots; mowing a lawn too short will favor crabgrass.

crabgrass closeup
Mowed crabgrass

Photos

Growth habit

Crabgrass growth habit

Photo: Bruce Ackley, The Ohio State University, Bugwood.org

Seedling

Crabgrass seedling

Photo: Rebekah D. Wallace, University of Georgia, Bugwood.org

Flower

Crabgrass flower

Photo: Rebekah D. Wallace, University of Georgia, Bugwood.org

Management in lawns

Cultural lawn care practices

  • Maintain healthy, dense turf that can compete and prevent weed establishment. Mow lawn at 3-4 inches high during the growing season and seed bare spots. 

Mechanical management

  • Hand pulling or using an appropriate weeding tool are the primary means of mechanical weed control in lawns. This is a viable option at the beginning of an infestation and on young weeds. Hand pulling when the soil is moist makes the task easier. Weeds with tap roots like dandelions or have a basal rosette (leaves clustered close to the ground) like plantain are easier to pull than weeds such as Bermudagrass (wiregrass) or creeping Charlie (ground ivy) that spread with stolons or creeping stems that root along the ground.

Chemical prevention/treatment in lawns

  • Herbicides should be used as a last resort because of the potential risks to people, animals, and the environment. Be aware of these lawn herbicide precautions first.
  • Apply a granular (apply with a spreader), selective, preemergent herbicide. There are numerous products on the market. Look for a preemergent without nitrogen fertilizer. Active ingredients include bensulidedithiopyr (offers postemergent control on young crabgrass seedlings), pendimethalinprodiamine, and siduron (can be applied when sowing grass seed). 
  • Rainfall or irrigation is required to dissolve the herbicide which is then absorbed into the upper portion of the soil and forms a barrier that kills weed seedlings. Preemergent grass herbicides have a residual activity that lasts for several weeks after application. High temperatures and rainfall will decrease the length of time they remain at sufficient concentration to be effective.

Tips for application

  • Apply prior to seed germination. For crabgrass, this begins when soil temperatures are above 55° for 3 days (during and shortly after, forsythia bloom is rough, but not consistently reliable, a guide for application timing). 
    • Soil Temperature Maps (linking to this site does not endorse any company, manufacturer, or product by University of Maryland Extension). 
  • Water after application, according to the label.
  • A second application may be possible, usually 6-8 weeks later (see label).
  • Consult label for the specific waiting period between application and overseeding.

If it is growing it can be spot treated with a postemergent herbicide before it matures and goes to seed. Look for the following active ingredients. 

Common Name: Quinclorac; Trade Name: Drive; others, can be combined with other active ingredients, Common Name: Fenoxaprop-p-ethyl; Trade Name: Acclaim Extra, others.