Crabgrass

(More lawn weeds)  

Large crabgrass
Digitaria sanguinalis 

Life cycle

Summer annual.

Growth habit

Grows up to 2 ft. tall; decumbent growth habit; swollen nodes. may root at nodes. Dies after the first frost in the fall.

Reproduction 

By seed. Seeds germinate from spring through late summer.

Conditions that favor growth

Mowing the lawn too short. Thin turf with bare spots.

Mowed crabgass

Management In Lawns

• Cultural Practices 
  Maintain healthy, dense turf that can compete and prevent weed establishment. Mow lawn at 3-4 inches 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 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: bensulide, dithiopyr (offers postemergent control on young crabgrass seedlings), pendimethalin, prodiamine, 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 which kills weed seedlings. Preemergent grass herbicides have 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° to 60°F for 7 to10 days (during and shortly after, forsythia bloom is a rough, but not consistently reliable, 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 label.
  • A second application may be possible, usually 6-8 weeks later (see label).
  • Consult label for specific waiting period between application and overseeding.
  • Corn Gluten for crabgrass control.

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. 

• Organic Lawn Herbicides

Publication: (PDF) TT43-Herbicides for Crabgrass and Goosegrass Control in Turf