Yard and Garden: Control Turfgrass Invaders

June 28, 2018, 9:47 am | Richard Jauron, Willy Klein

AMES, Iowa – The complete elimination of weeds in the lawn is not a practical goal for many homeowners. A more realistic approach is to minimize weed populations through various control measures. An attractive, well-maintained lawn is an important component of a home landscape.

Iowa State University Extension and Outreach horticulturists suggest ways to keep crabgrass and yellow nutsedge from reducing the aesthetic quality and vigor of the home lawn. For more information, contact the ISU Hortline at 515-294-3108 or hortline@iastate.edu.

crabgrass plant in lawn.How do I control crabgrass in the lawn?  

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, and 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 one-quarter 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, fertilization and irrigation. Crabgrass will have a difficult time germinating and surviving in a dense stand of turfgrass.  

In lawns that have had crabgrass infestations in recent years, an application of a preemergence herbicide in spring will effectively control crabgrass. To achieve control, the preemergence herbicide must be applied at the proper time and at the correct rate. Preemergence herbicides are normally 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.  

Postemergence control of crabgrass can be obtained with an application of a product containing dithiopyr, quinclorac or fenoxaprop. These materials are most effective when applied to small, actively growing crabgrass plants. The turfgrass may experience temporary discoloration from the use of some products.

How do I control yellow nutsedge?  

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. 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 warm summer months. It is often found in wet or poorly drained soils.

6Control of yellow nutsedge in gardens and lawns is difficult. Patience and persistence will be required.

The best way for home gardeners to control small infestations of yellow nutsedge in gardens is by hand digging. Carefully dig up plants with a small trowel or weeder. (If the plants are pulled, some of the nutlets will break off in the soil and sprout in a few weeks.) When digging yellow nutsedge, the objective is to remove the entire plant, including the roots and nutlets.

In lawns, yellow nutsedge can be controlled with herbicides. Multiple applications will be necessary. Begin applying herbicides in late spring/early summer when plants are actively growing but before they begin producing tubers. Products with active ingredients of sulfentrazone (Ortho Nutsedge Killer for Lawns), sulfentrazone plus prodiamine (Bonide Sedge Ender), and halosulfuron (SedgeHammer and Hi-Yield Nutsedge & Horsetail Control) provide the best control. Herbicides will likely need to be applied for two or three years to achieve effective control. The best way to prevent yellow nutsedge infestations in lawns is to maintain a healthy, dense stand of turfgrass by following proper cultural practices.


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