Glossy, rich green leaves make nut grass, also called nutsedge, look like a lush lawn grass, but it actually is a pesky perennial weed that's troublesome to eradicate. Not a real grass but a sedge (Cyperus rotundus) that is related to Egyptian paper plant, nut grass grows from a deep tuber called a nutlet. Pulling the plant often results in breakage, leaving the tuber to re-sprout, grow, bloom and then drop seeds.
Nut grass establishes and grows quickly when the soil is fertile and wet. In lawns, nut grass tends to manifest itself in low-lying areas where rainwater collects or where irrigation regimens or spray overlap, causing the soil to remain wetter than needed for the health of the turf grasses. The growth of nut grass and its spread via multiplying tubers and sprawling roots and occasional seeds is greatly reduced where soil is well-drained and turf grass is healthy and dense.
The University of Hawaii Cooperative Extension mentions nut grass seeds, tubers or roots are most often accidentally brought in to the garden from container-grown garden plants, freshly laid but infested sod, or from stowaway plant parts on maintenance equipment. Keep a keen eye on any items brought into your landscape to ensure you do not inadvertently bring nut grass into different parts of your garden. This weed is rarely spread by wind-blown seeds.
Combining several means of eradication helps remove nut grass from both planting beds or lawns. Examine the watering regimen and your soil--modifying irrigation or improving drainage naturally diminishes nut grass infestations in drier soils. Herbicides containing the active ingredients halosulfuron, sulfosulfuron or trifloxysulfuron sodium are most effective, according to the University of Hawaii. James McAffe of Texas A&M mentions imazaquin is effective, too. Product names with these chemicals include Sedgehammer, Monument, Manage, Image and Certainty. Monosodium methyl arsenate (MSMA) is also extremely effective to kill nut grass, according to Mississippi State University. Hand-pulling or digging up of entire plants including the tubers is also an option, especially if herbicides are not compatible with nearby ornamental plants.
Expect multiple applications of selective herbicides onto nut grass across the growing season for them to be most effective. Always follow product label directions for dosages, safe mixing/handling and proper timing of applications. The ideal time to apply herbicides is in spring when new growth is active and "tender" on the nut grass plants, although herbicide use is warranted in any season during green leaf presence. As leaves mature, their waxy coating is thickest and growth is lessened, diminishing the quick absorption of chemicals into the elongated leaf tissues. According to North Carolina State University, by early to midsummer, nut grass is already producing new rhizomes, increasing the potential for a weed infestation. Pre-emergent chemicals like Image and Pennant (metolachlor) are used to stop seeds from germinating anytime of year.
Carefully read all product labels when using selective herbicides. Some chemicals may kill the sedge, but any spray drift can cause severe damage on nearby ornamental plants. This concern is greatest when treating garden beds as compared to large expanses of lawn. For example, Image (imazaquin) kills the weed but is known to harm azaleas and viburnum shrubs. MSMA treats zoysia grass lawns but is harmful to a St. Augustine lawn. NCSU mentions that tubers remain dormant in soil for up to 10 years, so management of nut grass is a long-term commitment if full eradication is the goal.