Blog - Weeds in Gardens

Short answer: yellow nutsedge (Cyperus esculentus) has straw-yellow to golden-brown seedheads, lighter yellow-green leaves that taper to a long, needle-like point, and single, round tubers at the ends of its rhizomes. Purple nutsedge (Cyperus rotundus) has reddish-purple seedheads, darker green leaves with blunter tips, and tubers joined in chains. Both have solid, triangular stems and spread mainly from tubers buried 6 inches (15 cm) or more deep, which is why pulling rarely works. To get rid of nutsedge, spray a sedge herbicide such as halosulfuron, sulfentrazone or imazosulfuron while plants are young (before about the fifth leaf, in late spring or early summer), repeat as the label allows, fix wet spots, and expect to repeat the programme for two to three seasons. Nutsedge is a sedge, not a grass Both plants are often called nutgrass, but they belong to the sedge family (Cyperaceae), not the grass family. This matters because most grass killers, including crabgrass products, do not control them. Three quick checks tell you that you have a sedge: Triangular stem: roll the flower stem between your fingers. Sedge stems are three-sided and solid ("sedges have edges"); grass stems are round and usually hollow. Leaves in threes: leaves come off the base in three ranks, are thick, shiny and V-shaped in cross-section, and have no ligule or auricles where they join the stem. Fast summer growth: in a lawn, nutsedge stands above the grass a few days after mowing. According to Penn State Extension, it grows fastest in hot summer weather, when cool-season lawn grasses slow down. Yellow nutsedge vs purple nutsedge: identification table Telling them apart is worth the effort. NC State Extension notes that purple nutsedge is much harder to control than yellow, and some herbicides that work on yellow nutsedge only suppress purple. FeatureYellow nutsedgePurple nutsedge Seedhead colourStraw-coloured to golden-brownDark reddish to purplish-brown Leaf tipTapers gradually to a long, sharp, needle-like pointNarrows more abruptly to a blunter, rounded tip Leaf colour and widthLighter, yellow-green; 4 to 9 mm wideDarker green; 3 to 6 mm wide Height (unmown)Up to 3 ft (90 cm)Up to about 16 in (40 cm) TubersSingle, round, smooth, one at the tip of each rhizome; mild almond tasteSeveral in a chain along the rhizome, covered in red-brown scales; bitter SeedsProduces some viable seedAlmost none viable in the US ClimateMore cold-tolerant; the common one in northern and cool-season lawnsWarm climates; a bigger problem in southern and warm-season lawns Ease of controlDifficultHarder still The heights, leaf widths and tuber details come from the UC IPM identification pages for yellow nutsedge and purple nutsedge. In a mowed lawn you often will not see seedheads, so dig up a plant and look at the tubers: a single "nut" at the end of each runner means yellow, while beads on a string mean purple. The edible tiger nut, or chufa, is a cultivated form of yellow nutsedge, which is why its tubers taste of almonds. Yellow nutsedge: golden, straw-coloured seedheads. Photo: "Yellow Nutsedge" by The NYSIPM Image Gallery, CC BY 2.0 Purple nutsedge: reddish-purple to brown seedheads. Photo: "Cyperus rotundus flowerhead DC1" by Macleay Grass Man, CC BY 2.0 Why pulling nutsedge fails The part you see is the least important part of the plant. Nutsedge lives through winter as tubers (nutlets) and rhizomes. The UC IPM nutsedge guide says these can grow 8 to 14 inches (20 to 35 cm) deep, although most sit in the top 6 inches (15 cm), and they survive 1 to 3 years in the soil. Purdue Extension reports that one yellow nutsedge plant can make several hundred tubers in a single summer, and that dormant tubers can last more than three years. When you pull a plant, the stem usually snaps above the tuber, and the tuber simply sends up another shoot. UC IPM notes that a tuber uses about 60 percent of its reserves to produce its first shoot and 20 percent for the second, and mature tubers can resprout more than three times. So pulling only works if you are persistent: Pull or hoe every shoot before it has 5 to 6 leaves, because young plants have not yet started making new tubers. In summer that means every 2 to 3 weeks. Keep it up all season. Each removal drains the tuber a little more. For small patches in beds, dig out the soil to 8 to 10 inches (20 to 25 cm) and sift out every tuber. Do not put tubers in the compost; bin them or bag them (see how to dispose of invasive plants). Tilling or rotovating an infested bed makes things worse. It cuts rhizomes and spreads tubers through the whole area. Nutsedge (nut grass) coming up through a gravel bed from buried tubers. Photo: "Weed pest - nut grass" by robynejay, CC BY-SA 2.0 How to get rid of nutsedge with herbicides Selective sedge herbicides are the only practical way to clear nutsedge from a lawn without digging it up. They work by moving down from the leaves into the tubers, so the plant needs enough leaf to absorb the spray, but it must not be so old that it has already built a new crop of tubers. Timing Spray young, actively growing plants in late spring to early summer. Labels generally allow the 3 to 8 leaf stage, but UC IPM advises spraying before the fifth leaf. After that, it says, the herbicide may kill only the part above ground. In Pennsylvania, yellow nutsedge begins forming tubers in late June or early July. Purdue's advice is the same: early summer, when the plant is young and has not started producing tubers, is the ideal time. Do not mow for 2 to 3 days before and after spraying (Penn State). Mowing removes the leaf area the herbicide needs. Which active ingredient Active ingredientWorks onSpeed and repeatsNotes HalosulfuronYellow and purpleSymptoms in about 2 weeks; repeat after 6 to 8 weeks if neededThe standard homeowner choice; labelled on most cool- and warm-season lawns SulfentrazoneYellow; purple with repeatsFastest; injury visible within a few daysOften sold mixed with broadleaf herbicides; check lawn-type limits ImazosulfuronYellow and purpleLonger control; repeat after 21 days on heavy infestationsAmong the longer-lasting options for purple nutsedge MesotrioneYellow (suppression)Repeat after 2 to 3 weeksMainly for cool-season lawns; bleaches leaves white BentazonYellow onlyRepeat after 7 to 10 daysContact action; weak on purple nutsedge GlyphosateBothKills the lawn tooSpot treatment in beds or before renovation only Repeat intervals are from Penn State's product table and Purdue's efficacy ratings. For purple nutsedge in warm climates, the University of Arizona finds that halosulfuron gives about 2 to 4 weeks of control per application, while imazosulfuron and some professional sulfonylureas last 4 to 6 weeks or more. It recommends a follow-up application 4 to 6 weeks after the first, and limiting the programme to two summer applications of this herbicide group to slow resistance. Always check that the product lists your lawn grass. Many sedge products are labelled for both cool- and warm-season lawns, but rates and restrictions differ, especially on newly seeded grass. In vegetable beds, check the label for the crop before using anything. Contact products such as pelargonic acid, acetic acid or d-limonene only burn the leaves, and the tubers regrow. They buy time but do not eradicate nutsedge. Fix the drainage and the lawn Both nutsedges thrive in soil that stays wet. Purdue lists poor drainage and overwatering as the usual triggers, along with lawns mowed too short. Herbicides without these fixes just clear space for next year's tubers. Find the wet spots: nutsedge patches often map exactly onto low areas, downspout outlets, leaking irrigation heads and heavy clay. Redirect downspouts, repair leaking heads and regrade low spots with topsoil known to be free of nutsedge. Water less often, but deeply: letting the surface dry between waterings favours the lawn over the sedge. See the signs of an overwatered lawn. Relieve compaction: core aeration helps water move down instead of sitting on the surface. Our note on aerating after rain covers the right soil moisture. Mow at the top of the recommended range and feed on schedule so the lawn stays dense. Nutsedge is a sun-lover and weakens in shade, including the shade of a thick lawn canopy. Stop bringing it in: buy topsoil, sod and potted plants from nutsedge-free sources, and clean tillers, edgers and shovels after working in infested soil. In beds, a woven polypropylene landscape fabric under mulch suppresses nutsedge, but plastic (polyethylene) sheeting does not. UC IPM notes that nutsedge leaves can push through polyethylene, and even with fabric you still need to pull shoots that find the edges. What to expect season by season First season: one well-timed spray plus a follow-up usually clears most visible plants. Expect some regrowth from tubers that were dormant when you sprayed. Second and third seasons: shoots return in late spring from the surviving tuber bank. Purdue estimates that two to three years of herbicide control are needed to reduce viable tubers in the soil by 90 percent. The University of Arizona says repeating the same yearly programme will "eventually lead to manageable and acceptable" levels of purple nutsedge. Long term: once the lawn is dense, the drainage is fixed and you spot-treat the odd new shoot, nutsedge becomes an occasional nuisance rather than a takeover. Nutsedge often shows up in the same lawns as crabgrass, but the two need different products. If you are dealing with both, see our guide to crabgrass identification and control. FAQ Will a pre-emergent stop nutsedge? Standard crabgrass pre-emergents do not, because nutsedge comes back mainly from tubers, not seed. Some sedge herbicides, such as sulfentrazone, have some soil activity, but well-timed post-emergent sprays are the main tool. Does nutsedge die in winter? The leaves die back after frost, but the tubers survive in the soil and resprout the next spring once the soil warms. Sources UC IPM – Nutsedge (Home and Landscape Pest Note) UC IPM – Yellow Nutsedge identification UC IPM – Purple Nutsedge identification Penn State Extension – Lawn and Turfgrass Weeds: Yellow Nutsedge Purdue Extension – TURF-45: Controlling Yellow Nutsedge in Lawns NC State Extension – Purple Nutsedge University of Arizona Cooperative Extension – AZ1818: Strategy for Nutsedge Control in Turf