Large or Hairy Crabgrass, Digitaria sanguinalis
Small or Smooth Crabgrass, Digitaria ischaemum
University of Maryland, Home and Garden Information Center.
IPM Steps to Reduce Crabgrass
1. Sample for Pest
Confirm the presence of crabgrass before you treat.
Where to find it while inspecting: A grassy annual weed found in lawns and fields. Tolerant of poor soil and heat.
2. Proper ID
Is it crabgrass?
Size and Appearance: Large crabgrass has 2–6" long, fairly wide, “hairy” leaves. Seed heads are tall spikes with 2–9 “branches” which appear purplish when producing seed from mid-spring through fall. Look for it in disturbed areas of turf and soil. Can grow up to 2 ft. tall. Small/smooth crabgrass is low growing and does not have the fuzzy leaves of large crabgrass. The best way to identify any grass is by studying its nodes, collar, ligule, and sheath. See photos. Crabgrass is noticeable in lawns because it has a brighter color and bigger size than most turfgrasses.
3. Learn the Pest Biology
What is the life cycle of crabgrass?
Life Cycle: Crabgrass seeds are dormant for a short period of time after they shed from plants. Seed germination is related to soil temperature. When the soil temperature at the surface reaches 55°F for four or five consecutive days, crabgrass begins to germinate. Seeds germinate best from early spring to late summer. Crabgrass continues to grow until midsummer when days become shorter. Vegetative growth slows and plants enter their reproductive stage. Purplish seed heads form until frost kills the plants. Plants that emerge early in the season and have a long period of vegetative growth are much larger and more competitive than plants that germinate late in the season.
Preferred Food Sources: Crabgrass grows well in hot dry conditions, and poor soil, and will out compete turfgrasses that are under heat stress.
Preferred Habitat: Large crabgrass grows well in both lawn and field. Small/Smooth is more often found in turfgrass.
4. Determine Threshold
How much crabgrass is too much?
Threshold: Due to the prolific production seed heads, act when you see crabgrass encroach.
5. Choose Tactics
Creating a healthy soil condition and understanding turfgrass needs is the first step in reducing turf pests. What can I do to treat, reduce, or prevent crabgrass?
Best Management Practices: Maintain proper soil pH: 6.0 to 6.8 (test every 3–5 years). Fertilize at the proper time for turfgrass root development, primarily fall (late spring at times when turf is weak and thin), irrigate if needed, mow at proper height (removing no more than 1/2 of the blade, amend poor soil, choose proper turfgrass seed for your conditions, buy quality seed, overseed thin spots in fall or early spring, remove thatch. Take steps to maintain shoot density and rooting.
Treatment Methods: The basic principle of a crabgrass management program is to prevent re-infestation by seeds. Controlling seed production for several years will help reduce the viable seed supply. Crabgrass cannot be controlled in one growing season because of the great number of viable seeds that accumulate in the soil from years of infestation. A good weed management program in sports fields is one that consists of both focused cultural practices and the use of herbicides as appropriate for the control of any given species. Satisfactory control may require several seasons of conscientious adherence to a good management program. Establishing a dense and healthy stand of turfgrass is the best way to control crabgrass and other annual weeds including grasses and broadleaf weeds. The proper mowing height and frequency, fertilization and irrigation are part of a sound weed control program and should be practiced throughout the growing season. Seed in late summer for new lawns. Crabgrass will die out after fall frost. Mow at 2–3" to “shade” the soil and keep it cool. Water deeply once a week rather than frequent light irrigation during drought conditions. Avoid summer fertilization because crabgrass benefits more than turfgrasses at this time, unless the turf is being used for summer sports, and is irrigated, in which case there should be moderate fertilization provided (minimum 50–75% slow release nitrogen).
Was the tactic successful? Record the date pests were first noted, and the tactic you used, and its success. Use one of our RECORD KEEPING tools.
For More Information:
When a pesticide application is necessary, all necessary and required precautions are taken to minimize risk to people and the environment and to minimize risk of pesticide resistance or pest resurgence. Pesticide use in your school may be prohibited or regulated by local policies or state and federal regulations. Risk reduction methods can include, but are not limited to, spot-treatment, the use of gel or paste bait formulations placed in inaccessible locations, injection into a crack or crevice, and other methods that reduce potential exposure.