Nutgrass is a very common weed found in yards. It is also called nutsedge, and although it appears to be a grass it is actually a sedge. Sedge is a close relative of turfgrasses and enjoys the same conditions that most lawns need. It is very hard to eradicate because it has a root system that can go down 2 feet or more into the soil.
Nutgrass is a perennial and dies back after temperatures begin to decrease. The weed can spread by tubers, rhizomes or seed and is comfortable in any type of soil. Although nutgrass looks like a turfgrass, it can be distinguished by its triangular stem. The leaves are thicker than grass and arranged in groups of three. There are purple and yellow nutgrasses, which can be identified by the color of the seed head. Yellow nutgrass is more cold-tolerant than purple, and purple seems to be harder to get rid of. Yellow nutgrass grows 12 to 16 inches tall and purple is only 6 inches high. It is important to tell which you have as each has different resistance to different herbicides.
Nutgrass control consists of chemical, mechanical and cultural measures. Cultural control includes amending the growing environment and ensuring that your turfgrass is resistant to chemical nutgrass herbicides. Mechanical control means digging up chunks of sod as deep as 10 inches and 8 to 10 inches out from the clump. Chemical controls have limited effectiveness and it is important to apply herbicides at the right time and on the right turf to ensure penetration of the weed's density.
Selective and Nonselective Herbicides
Nonselective herbicides are broad-spectrum weed killers. They do not differentiate between weed species. The only nonselective herbicide to use on nutgrass is glyphosate, which is the active ingredient in Round-Up. It doesn't work well on adult nutgrass so must be applied to the emerging seedlings. Repeat applications are necessary. Halosulfuron and MSMA are post-emergent selective herbicides for use on nutgrass. They also must be applied to the plants when they are young, especially before the sixth leaf appears. Both of these herbicides move through the plant quickly and, unlike glyphosate, do not require reapplication if applied according to instructions.
Pre-emergent herbicides are applied before problem weeds occur, generally at the end of the growing season or in late winter before weeds have begun to sprout. There are no pre-emergents that control purple nutgrass but there are several that will reduce the population of yellow nugrass. Of these, only dichlobenil is available to home gardeners. Pre-emergents are not for use on turfgrass but can safely be used around most ornamentals, although it is best to check the package to make sure your plants are on the safety list.
Nutgrass tubers are spread by cultivation and will often come to the home garden from plant stock that was purchased. They can spread on infected tools and the seed and tubers can persist in the soil for years. It is important to inspect all new plants before bringing them home to avoid contaminating your yard. Nutgrasses prefer moist soil and their presence can indicate an irrigation issue. Correcting drainage and irrigation systems can help prevent the spread of this nuisance weed.