Kyllinga: identify it, treat it, keep it out

Start with the stem. Roll one between your thumb and finger. Does it feel triangular? Then you are looking at a sedge, and the next question is which one. Look at the top of a flowering stem. Kyllinga carries a single round, light green seed head about 3/8 inch across, sitting on three leaves that radiate out like a star, per UC IPM. A branched, spiky seed head points to yellow nutsedge instead.

No seed heads yet? Dig up a small piece. NC State TurfFiles notes that kyllinga spreads by well-developed rhizomes and produces no tubers, and LSU AgCenter describes those rhizomes as red to purple. If you find small, hard nutlets on the roots, nutsedge moves back to the top of the list. If you find a mat of reddish runners and no nutlets, you have kyllinga.

Green and false-green kyllinga look so alike that NC State groups them together under one name. You do not need to separate them for a home lawn. The plan below is built from sources covering both.

Where is the mat? If it sits around a sprinkler head, a downspout, a leaking valve, or a low spot that holds water after rain, the location is the clue. LSU AgCenter says green kyllinga prefers low areas with wet soil and is usually an indicator of poor drainage, and that poorly drained or overwatered lawns are ideal habitat. Rutgers goes further and treats a false-green kyllinga patch as a sign of chronically excessive soil wetness.

Want to confirm it? Push a screwdriver or soil probe into the patch the day after you water, then do the same in a healthy part of the lawn. If the kyllinga spot is still soft and wet while the rest has dried, that is the condition to fix. Herbicide can clear the mat, but it will move back in while the soil stays that way.

The rhizomes explain the rest. A mat is one connected network, and UC IPM warns that hoeing breaks rhizomes into smaller pieces that keep growing. It also names equipment sanitation as the best prevention, because rhizome pieces ride on mowers and tools into new spots. Kyllinga tolerates low mowing too, per LSU, so a short cut does not slow it down.

Fix the water first. Repair leaks, cut back irrigation on that zone, and improve drainage where you can. Then pick a removal route that matches the size of the problem.

For a small patch, dig. Take the mat out with the top few inches of soil so the rhizomes come with it, and refill the spot with soil and seed or sod. Rutgers notes that a sod cutter works on larger areas as long as it cuts deep enough to take the rhizomes.

For mats too big to dig, a sedge herbicide is the standard route. Halosulfuron, sold to homeowners as SedgeHammer, controls green kyllinga, and UC IPM says two sequential applications give the best control. NC State's halosulfuron fact sheet says to treat plants that are actively growing, repeat in 6 weeks, and stay within two applications a year. Rutgers, writing for cool-season turf, spaces the two halosulfuron applications 4 weeks apart, lists sulfentrazone and imazosulfuron as the other options for false-green kyllinga, and says to wait 4 weeks before seeding a treated area.

Which products are safe on your grass? On warm-season lawns, LSU AgCenter lists halosulfuron, sulfentrazone, imazaquin, and the thiencarbazone, iodosulfuron, and dicamba mix as safe on St. Augustine, centipede, zoysia, and bermuda, and limits trifloxysulfuron to zoysia and bermuda. Those tables are a starting point. The label on the bottle you buy decides, so confirm it lists your grass type before you mix anything.