Nutsedge in St. Augustine: How to Identify It and Get Rid of It
Nutsedge (nutgrass) grows faster than your lawn and shrugs off most weed killers. How to identify it, why pulling makes it worse, and the product made for it.
The short version
- Nutsedge (often called nutgrass) is a sedge, not a grass, so most weed killers miss it.
- Don't pull it. It leaves underground tubers ("nutlets") behind that sprout again.
- Use a product made for sedges, like halosulfuron (SedgeHammer), which is labeled for St. Augustine.
- Treat while it's young, and expect a follow-up application.
How to identify nutsedge
- Grows faster than the lawn. A day or two after mowing, it's poking up above everything else.
- Shiny, light-green or yellow-green leaves with a stiff ridge down the middle.
- Triangular stem. Roll it between your fingers and you'll feel the edges. "Sedges have edges."
- Loves wet spots and areas that are overwatered or drain poorly.
The two common types are yellow nutsedge and purple nutsedge. Both are controlled the same way.
Why pulling makes it worse
Nutsedge spreads through underground tubers. When you pull the top, the tubers usually snap off and stay in the soil, and each one can send up new plants. Pulling can also wake up dormant tubers.
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How to kill it
Halosulfuron, sold as SedgeHammer and in other products, is labeled for St. Augustine and controls both yellow and purple nutsedge. From the product label:
- Skip mowing for 2 days before and 2 days after spraying.
- Spray when temperatures are 85°F or below and no rain is expected for at least 4 hours.
- Add a non-ionic surfactant as the label directs. Sedge leaves are waxy and shed spray without it. The surfactant I use is Southern Ag Surfactant for Herbicides.
- Use a pump sprayer, not a hose-end sprayer, and spray until the leaves are wet.
- Results show in about 5 to 7 days, with full die-back over a couple of weeks.
- Don't treat stressed, new, or recently plugged turf.
Check the label for the follow-up interval. A second application is common for heavy patches.
I use sulfentrazone, Prime Source Sulfentrazone 4SC Select, the same active ingredient as Dismiss. Follow the label rate for St. Augustine.
Prevent it
Nutsedge is a sign of too much water. Check sprinkler run times with the tuna can test, fix soggy spots, and water deeply but less often. A thick lawn mowed at the right height also shades it out.
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