How do I control water grass in my lawn?
“Water grass” is an ambiguous name. Several plants are occasionally referred to as water grass. Two common lawn weeds that are sometimes referred to as “water grass” are crabgrass and yellow nutsedge.
Crabgrass (Digitaria spp.) is an annual, warm-season grass. Crabgrass seeds begin to germinate when soil temperatures reach 60 degrees Fahrenheit. Germination usually begins about mid-April in southern Iowa, early May in northern parts of the state. Crabgrass continues to germinate over several weeks from spring into summer.
While crabgrass seed germination begins in spring, plants don’t become highly visible in lawns until late spring/early summer. Crabgrass is a low growing, spreading plant with light blue-green foliage. The leaf blades are approximately 1/4 inch wide. Seedheads appear as several finger-like projections at the top of the main stem. Crabgrass grows rapidly during warm summer weather. Growth slows with the arrival of cooler temperatures in late summer. Plants are destroyed with the first hard frost in fall. However, before it dies a single crabgrass plant can produce thousands of seeds.
The best way to prevent crabgrass infestations in lawns is to maintain a thick, healthy lawn through proper mowing, irrigation, and fertilization. Crabgrass will have a difficult time germinating and surviving in a dense stand of turfgrass. Gardeners who have had crabgrass problems in recent years will need to apply a preemergence herbicide in spring.
The keys to successful control of crabgrass in lawns are correct timing of the preemergence herbicide application and proper application of the material. Preemergence herbicides should normally be applied in early to mid-April in southern Iowa, mid-April to May 1 in central Iowa, and late April to early May in northern areas of the state.
Yellow nutsedge (Cyperus esculentus) is a warm-season perennial. It is not a grass nor a broadleaf weed, but a sedge. The grass-like leaves are light green to yellowish in color and shiny in appearance. Yellow nutsedge is an erect plant. The stem near ground level is triangular. The leaves come off the stem in sets of threes. Yellow nutsedge reproduces by seed and small underground tubers called nutlets. Flowers are yellowish or yellowish brown and are borne on small spikelets. Yellow nutsedge grows most rapidly during the hot summer months. It is often found in wet or poorly drained soils.
Control of yellow nutsedge is difficult. Plants do pull easily. However, when plants are pulled some of the underground nutlets remain in the soil. Eventually, the nutlets sprout and the plants reappear. Several herbicides will effectively control yellow nutsedge in lawns. Effective herbicides include Basagran (bentazon), Dismiss (sulfentrazone), and Certainty (sulfosulfuron). These materials are generally not available to home gardeners. However, they can be applied by professional lawn care companies.