Submitted by Jim Crawford, Field Specialist in Agricultural Engineering, University of Missouri Extension, Atchison County
I have been receiving many inquiries this spring about a fast growing, yellowish grass-like weed in home lawns and turf. It grows faster than the surrounding lawn so it is quite noticeable shortly after mowing. The culprit is yellow nutsedge which is also called nutgrass or watergrass.
Yellow nutsedge is a relatively common problem in lawns, especially in wet years or in lawns with irrigation. Even though it is dry now, we had adequate rainfall in the spring to promote growth of this weed. Although it looks much like a grass, its official classification is a sedge. Unlike grasses, sedges have triangular stems, and the leaves come off the stems in three different directions as opposed to two directions for grasses. Yellow nutsedge is pale green to yellow and grows rapidly in the spring and early summer. Because of this rapid shoot growth, it sticks up above the rest of the lawn only a few days after mowing. This weed is a good indicator of poor drainage, but it can be introduced into well-drained sites through contaminated topsoil or nursery stock.
As with many weeds, nutsedge is less competitive in a dense, healthy lawn than in an open, poor lawn. Increasing soil’s infiltration/ drainage is a good way to help control this weed. If you have a larger area infested with nutsedge, core aerating your lawn this fall will help improve your lawn’s infiltration and thus reduce the favorable habitat for this weed. Mowing the grass too short also promotes the growth of this weed.
Nutsedge is difficult to control culturally because it produces numerous tubers that give rise to new plants. Pulling nutsedge will increase the number of plants because dormant tubers are activated. However, it is possible to control nutsedge by pulling, but you must be persistent. If you are, eventually the nutsedge will die out.
If you decide persistent pulling is not for you and you wish to treat with an herbicide, it would be better to leave the nutsedge plants undisturbed so the herbicide can be maximally translocated to the roots, rhizomes, and tubers. Herbicides used to control dandelions and other broad leaf weeds will have no effect on nutsedge; however, several herbicides are labeled and available for nutsedge control. Herbicides that contain halosulfuron or sulfentrazone are recommended for yellow nutsedge control. Regardless of herbicide selection, yellow nutsedge is a difficult-to-control weed that may require multiple herbicide applications. Follow label directions about when to make follow-up applications, if needed.
Late spring/early summer is the ideal time to apply a herbicide to control yellow nutsedge. During its early growth stages, yellow nutsedge has not started producing tubers and is most susceptible to herbicides. As the summer progresses, plants form seedheads and tubers which are much more difficult to control. It is critical to control nutsedge early in the summer before it produces tubers. However, be aware that two to three years of control using herbicides will be needed to reduce viable tubers in the soil by 90 percent. Herbicide applications will injure growing yellow nutsedge plants and help prevent more tubers from forming, but herbicide applications will not control tubers that are viable in the soil but have not yet produced plants. Make sure you fully read, understand and follow all label directions before you apply any chemical to your lawn.