Herbicides for purple nutgrass (Cyperus rotundus) and yellow nutgrass (Cyperus esculentus), also referred to as nutsedge, are available in both pre-emergent and post-emergent forms. Nutgrass, an invasive weed that infests lawns and ornamental beds, can be controlled through proper use of herbicides. Without treatment, nutgrass can seriously affect your garden or landscaping by diminishing the health of plants that cannot compete.
As a pre-emergent herbicide control for nutgrass, North Carolina State University Cooperative Extension service suggests using metolachlor. Pre-emergent herbicides are chemicals applied before weeds emerge from the soil. Apply metachlor before desired plant growth begins to bud to prevent injury from chemical exposure. Being careful to keep metachlor from coming into contact with new plant growth, control weeds with another herbicide application approximately eight to 10 weeks after initial use.
Imazaquin is another pre-emergent herbicide used for nutgrass that may also be used as a post-emergent treatment (applied after weeds have emerged from soil). According to the NCSU Extension, imazaquin damages several plants used in landscapes and gardens, such as azaleas. Be mindful of your landscape if you choose to utilize this nutgrass herbicide.
Halosulfuon is a type of post-emergent herbicide used to control both yellow and purple nutsedge mainly in turfgrass, but it is also effective in ornamental beds. NCSU Extension Service recommends the first treatment application of halosulfuon during May or June; apply to "young nutsedge sprouts when plants have three to eight leaves." For control that will last all season long, use a second application approximately six weeks after initial use.
Bentazon is a type of post-emergent herbicide used for control of nutgrass. Apply the first treatment early during the summer season, as directed by the NCSU Extension. A treatment application when yellow nutsedge has emerged and reached a height of 6 to 8 inches is ideal with a follow-up application for regrowth within approximately 7 to 10 days after initial use.