Nutsedge, commonly referred to as nut grass, is a persistent and aggressive perennial weed that infests lawns, gardens, and agricultural fields across the United States. Because it is a sedge, not a true grass, it cannot be controlled by most conventional grass or broadleaf weed killers. Two primary varieties exist: yellow nutsedge (Cyperus esculentus) and the more troublesome purple nutsedge (Cyperus rotundus). Nutsedge is notoriously difficult to eradicate because of its extensive underground system of tubers, often called “nutlets.” A single plant can produce hundreds or even thousands of these nutlets, which remain dormant in the soil and sprout new plants even after the visible foliage is removed.
Effective Chemical Active Ingredients
Effective control of nutsedge requires specialized post-emergent selective herbicides designed to target the unique biology of sedges. The two most common and successful active ingredients are Halosulfuron-methyl and Sulfentrazone. These compounds are systemic, meaning they are absorbed by the leaves and translocated down into the underground rhizomes and nutlets, disrupting the plant’s entire structure.
Halosulfuron-methyl, often sold under brand names like SedgeHammer, works by inhibiting the acetolactate synthase (ALS) enzyme. This enzyme is responsible for synthesizing branched-chain amino acids necessary for cell division and plant growth. Blocking this process starves the plant and halts its ability to generate new tissues, including new nutlets. Halosulfuron-methyl is effective against both yellow and purple nutsedge, although visible results are slow, taking two to four weeks to fully kill the plant.
The other primary active ingredient, Sulfentrazone, inhibits the protoporphyrinogen oxidase (PPO) enzyme. This disruption interferes with the plant’s chlorophyll production pathway, causing a buildup of highly reactive compounds that destroy cell membranes when exposed to light. Sulfentrazone, often found in combination products, is effective at controlling yellow nutsedge and provides a much faster visual kill, with symptoms appearing within days. While it offers suppression of purple nutsedge, the tougher variety usually requires multiple applications or the use of Halosulfuron-methyl for complete control.
Timing and Application Strategies
Successful nutsedge eradication depends heavily on precise timing and application technique to ensure the herbicide reaches the underground tubers. The initial application should occur when the nutsedge is young and actively growing, typically in late spring or early summer, before the plant begins to form new nutlets. Treating the weeds when they are small, ideally at the three- to eight-leaf stage, maximizes the systemic herbicide’s ability to move to the roots.
Systemic herbicides translocate most effectively when temperatures are moderate, ideally between \(60^\circ\text{F}\) and \(85^\circ\text{F}\). Applying the product during excessive heat (above \(90^\circ\text{F}\)) can cause the plant to become stressed, which slows its metabolic rate and reduces chemical absorption. The nutsedge leaf surface is waxy, causing water-based sprays to bead up and roll off, so a non-ionic surfactant (NIS) must be added to the spray mixture. The surfactant acts as a wetting agent, reducing the surface tension of the water droplet and helping the herbicide spread evenly and penetrate the leaf cuticle.
The most important strategy is the sequential application, as a single treatment only kills the visible shoot and not all the dormant nutlets. Repeat applications are mandatory because new plants will continue to sprout from the unaffected tubers over a period of weeks. Most product labels recommend a second application four to six weeks after the first, which is the necessary interval to treat the new growth before it develops new nutlets.
Selecting the Right Herbicide and Safety Precautions
Selecting the correct nutsedge herbicide involves balancing the weed-killing power with the tolerance of the surrounding turfgrass. For instance, while Halosulfuron-methyl is safe for most major warm- and cool-season turfgrasses, Sulfentrazone can cause temporary discoloration or thinning on sensitive varieties like St. Augustine or Centipede grass, especially if the grass is already stressed by heat or drought. The product label is the final authority and must be consulted to ensure the chosen active ingredient is safe for the specific lawn environment.
Handling concentrated chemical products requires safety protocols to protect the applicator from exposure. Personal protective equipment (PPE) includes:
- Chemical-resistant gloves.
- Eye protection like splash-proof goggles.
- Long-sleeved shirts.
- Long pants.
Herbicides should always be mixed outdoors in a well-ventilated area. The concentrated product should be poured carefully into a partially filled tank of water to prevent splashes. To maximize uptake, avoid watering the lawn for 24 hours before and after application, and do not apply the spray if wind speeds are high, which can cause chemical drift onto desirable non-target plants.