Smooth crabgrass ( Digitaria ischaemum ) and large crabgrass ( Digitaria sanguinalis ) are two common crabgrass species found in turfgrass throughout the U.S. Crabgrass is a pale green colored summer annual weed causing an unsightly mottled look to dark green turf. Germination begins when soil temperatures are approximately 55 - 60 ̊F for 3 to 10 consecutive days at a soil depth of 2 to 4 inches. Crabgrass can produce up to 150,000 seeds per plant, which may remain viable in soil for several years. Because of this, crabgrass is one of the most troublesome weeds to manage.
Crabgrass can grow under adverse growing conditions and often grows faster than the desirable turf. It takes advantage of canopy voids in desirable turf created by scalping, low mowing heights, insufficient nutrient availability or thinned areas due to other pest damage or pressure. Crabgrass can survive in wet or dry areas.
Crabgrass plants have pointed leaf tips with round stems and leaf blades typically longer CRABGRASS than two inches. Both smooth and large crabgrass have tall, membranous ligules at the base of the leaf blade. Smooth crabgrass plants do not have hairs on the leaf sheath and will typically have a red to maroon color at the base. Large crabgrass plants have hairs on the leaf and sheath. Both species produce seed heads with finger-like spiked branches. Large crabgrass produces 2 to 9 finger-like branches and smooth crabgrass produces 2 to 6. Both crabgrass species produce seed from mid-summer until frost.
Like all weeds, crabgrass seed requires light to germinate. A dense, healthy turf can reduce crabgrass populations. Factors such as disease, insects, improper mowing, low fertility and drought can weaken or thin turf. Thinned or weakened turf stands will allow more light to reach the soil surface where seeds are waiting to germinate below the canopy. Crabgrass will take this opportunity to germinate and quickly spread. Proper cultural practices such as mowing, fertilization and watering can help turf resist invasion by crabgrass.
There may be times when turf managers are unable to make timely preemergent herbicide applications as a result of poor weather conditions during the optimum application window. Inevitably some break-through may occur with the use of preemergence applications, which will require postemergence herbicide applications. Postemergence crabgrass control can be effectively achieved with Solitare ® WSL Herbicide. Solitare WSL is a water-soluble liquid formulation, containing two active ingredients (sulfentrazone and quinclorac) in a ratio specifically designed to provide postemergence crabgrass control in most growth stages. Solitare WSL applied at 4 fl oz/1000 sq ft offers control of a much broader weed spectrum than the individual active ingredients alone and provides unsurpassed speed of control with long lasting residual.