Nutgrass (Rotundus)

The Nutgrass (Rotundus) is generally described as a perennial graminoid. This is not native to the U.S. (United States) .

Uses of : Landscaping, Medicinal, Culinary, etc.

Ethnobotanic: Purple nutsedge has been used in traditional medicine and in landscaping in China. There are reports of its use in India as a soil binder. It is undesirable as fodder, because it quickly becomes fibrous with age, but in the absence of more desirable plants, it can serve that purpose (Holm et al. 1977). Extracts and compounds isolated from purple nutsedge have medicinal properties such as the reduction of fever, inflammation, and pain. The literature contains numerous references to the use of this plant’s roots for essential oils and its seeds for food products. Tuber extracts may reduce nausea and act as a muscle relaxant (Wills 1987).

Noxiousness: Purple nutsedge, has been called the “world’s worst” weed. A befitting designation for a species known from more countries (at least 92) than any other weed that infests at least 52 different crops worldwide (Holm et al. 1977). It grows in all types of soils and can survive the highest temperatures known in agriculture. In the United States, purple nutsedge infests cultivated fields, waste areas, roadsides, pastures, and natural areas. It is considered a headache for the southern gardener because of its insidious, rapid growth in flowerbeds and vegetable gardens. Purple nutsedge produces an extensive system of underground tubers from which they can regenerate. Nutsedge is very difficult to control once it is established.

Purple nutsedge greatly impacts agriculture and has an unfavorable effect on natural ecosystems by displacing native plants or by changing the availability of food or shelter for native animals. Although relatively small in stature, purple nutsedge provides formidable resource competition for much larger crop plants and ornamentals. This rapid growing plant can quickly form dense colonies due to its ability to produce an extensive system of rhizomes and tubers. Many studies document reduced yields in sugar cane, corn, cotton, rice, vegetables, and numerous other crops. The abundantly produced tubers present an efficient means of dispersal and reproduction. These features together with the ineffectiveness of herbicides make this weed nearly indestructible.

Impact/Vectors: Reduction in crop yields is one of the greatest impacts of this species. In extreme cases purple nutsedge can reduce sugarcane yields by 75% and sugar yields by 65%. In Australia, in experimental plots with cultivation, sugarcane yield was reduced by 38%. In Colombian cornfields, when purple nutsedge was allowed to grow for 10 days, yield was reduced by 10%. If allowed to remain for 30 days, yield dropped to 30%. Similar dramatic effects of this weed on cotton, corn, tomatoes, tobacco, mulberries, lemons, and many other crops have been demonstrated (Holm et al. 1977).

Rochecouste (1956) noted that even in humid regions the production of purple nutsedge shoots and tubers could severely restrict water availability to sugarcane. Approximate quantities of fertilizer that may be mobilized and stored in purple nutsedge equal 815 kilograms of ammonium sulfate, 320 kilograms of potash, and 200 kilograms of phosphate per hectare (Holm et al. 1977).

Besides resource competition, evidence suggests that organic substances released from the decay of dead subterranean tissues may be allelopathic and reduce crop yields where purple nutsedge infestations are severe. Purple nutsedge may produce up to 40,000 kilograms of subterranean plant material per hectare. Under experimental conditions, barley yield was reduced by 15 to 25% by Cyperus rotundus residues in the soil (Horowitz & Friedman 1971).

Tuber and rhizome production are important factors in this species’ success as a weed. Rhizomes provide the major means by which the plants may colonize an area. Tubers offer a mechanism for asexual reproduction, and they are the major dispersal unit that can survive extreme conditions. Tubers make the plant difficult to control, because only translocated herbicides are po

General Characteristics

General: Purple nutsedge is a colonial, herbaceous, perennial with fibrous roots that typically grows from 7-40 cm tall and reproduces extensively by rhizomes and tubers. The rhizomes are initially white and fleshy with scaly leaves and then become fibrous, wiry, and very dark brown with age. Rhizomes may grow in any direction in the soil. Those growing upward and reaching the soil surface become enlarged forming a structure 2-25 mm in diameter variously called a “basal bulb, a tuberous bulb, or a corm” that produces shoots, roots, and other rhizomes. Rhizomes that grow downward or horizontally form individual tubers or chains of tubers. Individual tubers are dark reddish-brown when mature, about 12 mm thick, and vary from 10-35 mm long.

The dark green, shiny, three-ranked leaf blades arise from or near the base of the plant. They are narrow and grass-like ranging in size from 5-12 mm wide to 50 cm long and have a prominent channel in cross section. The leaf sheaths are tubular and membranous and attach to compact nodes at or near the base of the plant.

The upright culms or stems are 10-50 cm tall, smooth, triangular in cross section, and support a much-branched inflorescence. Two to four leaf-like bracts subtend the inflorescence which is umbel-like consisting of 3-9 unequal length branches (sometimes referred to as rays) bearing spikes of 3-10 spikelets. Spikelets are flattened and linear ranging in length from 10-30 mm long, and generally dark reddish purple or reddish brown in color. Each of the 20 or so flowers (florets) in a spikelet are each subtended by a keeled scale (glumes) 2-5 mm long that have a green midvein and a membranous margin. The flowers are bisexual each with three stamens and a pistil bearing three stigmas. Fruit, although rarely produced, consists of a three-angled achene (nutlet).

Purple nutsedge possesses the C4 photosynthetic apparatus, which is an adaptation to assimilating CO2 at higher temperatures and higher light intensities compared to C3 pathway plants. C4 plants typically exhibit their best growth rates at temperatures characteristic of tropical and subtropical regions. The leaf anatomy for purple nutsedge is of the Krantz-type. Sheaths of cells that form around the vascular bundles serve to compartmentalize the photosynthetic events. Greater anatomical and physiological details for purple nut sedge are given by Wills (1987).

Cyperus esculentus, yellow nut sedge, is another problematic weedy species that reproduces by tubers. It is more widespread and also grows in more temperate parts of the United States. Purple nutsedge is readily distinguished from yellow nut sedge and other sedges by its purplish brown spikelets and scaly or wiry rhizomes that often bear chains of tubers.

Required Growing Conditions

Purple nutsedge is reportedly native to India, but it has been introduced around the World (Holm et al. 1977). The plant is a serious pest in the Southeast ranging from Virginia to central Texas. It also has become established in parts of Arizona and California and has the potential to invade other Pacific states. (Southern Weed Science Society 1995; FICMNEW 1997). This species occasionally occurs in more temperate regions. For example, its presence in Stearns County, Minnesota was documented by a specimen in the University Herbarium collected by J. E. Campbell, July, 1896 (MIN: accession number 81217), but purple nutsedge has not persisted there and other cold locales. The northern limit of nutsedge in Japan is in a region where the average minimum atmospheric temperature is -50C, the temperature below which tubers will not germinate (Ueki, 1969). Temperature appears to limit the species to more tropical and warm temperate regions. For current distribution, please consult the Plant Profile page for this species on the PLANTS Web site.

Control For control measures that are pertinent to your area, please contact your local agricultural extension specialist or your city/county weed control specialist.

Mechanical: Moisture loss is detrimental to tubers. Tuber death ensued after moisture content dropped to 15% or less. Tubers left at the surface of dry soil exposed to full sun desicated beyond recovery after 4 days. Under simulated field conditions, tubers at 5 and 10 cm depths in dry soil that were protected from rain but exposed to sunlight were killed after 8 and 12 days at those respective depths (Holm et al., 1977).

Purple nutsedge tubers can be destroyed with repeated summer tillage because of their susceptibility to drying. Infested fields plowed or disked at three-week intervals for the entire growing season reduced tuber number by 80%. At four-week tillage intervals, tuber numbers actually increased. Summer dry fallowing is most effective in light, sandy soils but less so in wetter, heavier soils. Springtooth harrows are an excellent implement for this method. Such tillage methods are often impractical, because the land cannot be used for one or more growing seasons. An exception would be where October to June cropping is feasible (Holm et al. 1977).

Where tillage is possible, it can give crops a competitive advantage. The use of precision equipment to cultivate as closely as possible, and hand or mechanical thinning can help to reduce nutsedge competition. Nutsedge is susceptible to shading, which reduces vegetative growth and tuber production.

Chemical: Purple nutsedge has proved difficult to control with herbicides. To be effective, the herbicide must be translocated throughout the rhizome and tuber network of the plant. Always follow the manufacture’s recommendations for application and observe all precautions when using herbicides. Also, observe applicable local, state, and federal regulations. A few case histories of herbicide control are cited to indicate progress being made in controlling purple nutsedge.

Field experiments over a 10 year period were conducted at the USDA, Southern Weed Science Lab, Stoneville, Mississippi, to determine the effects of tillage and herbicide inputs on purple nutsedge control in cotton. Four tillage cotton production systems (conventional, two levels of reduced-tillage and no-tillage) were evaluated with two herbicide (glyphosate) input levels each. For the most part, seed cotton yields were equivalent for the conventional and reduced tillage production systems regardless of the herbicide input level. Seed cotton yields were less in no-till systems 6 of 10 years regardless of herbicide input levels. It was discovered that the timing of glyphosate application, as a preplant foliar treatment, was extremely important. Purple nutsedge control decreased (i.e., nutsedge populations increased) with glyphosate applications 2 to 4 weeks prior to cotton pl

General Upkeep and Control

DAGL"Under dryland conditions the new planting should not be grazed until late summer or fall of the second growing season. The plants may be severely damaged by overgrazing especially in the seedling year. Under irrigated conditions the new planting should not be grazed until late summer or fall of the first growing season. The plants may be severely damaged by grazing too soon.

Use no more than 60% of the annual growth during the winter season or 50% during the growing season. Close grazing in the fall is consistently associated with winterkill. This plant responds well to rotation-deferred grazing systems. Periodically the grass should be allowed to mature and produce seed for continuation of the stand.

Orchardgrass responds very well to good fertility management. It is one of the most responsive pasture grasses to nitrogen applications. One strategy to even out the forage production is to fertilize the stand after the first and second cutting or grazing period to boost late spring and summer production. Apply fertilizer based on soil tests.

Seed Production When planting for seed increase, recommended row spacing is 28 to 40 inches. Seeding rate is 1.5 to 2 pounds PLS per acre to seed 25 to 30 PLS per linear foot of row. Irrigated seed yields are commonly 250 to 300 pounds per acre. Seed matures evenly and is ready for harvest in mid-July. Windrowing followed by combining is the preferred method of harvest. When direct combining the seed should be dried to 12 percent moisture in bins and 15 percent moisture in sacks before storing.

Pests and Potential Problems Brown stripe, scald, rust and leaf spot are the most prevalent and destructive disease in orchardgrass. Resistance to these varies among DAPU3.PG (American wild carrot)"

Plant Basics
General Type Graminoid
Growth Duration Perennial
Plant Nativity Introduced to U.S.

Source: USDA, NRCS, PLANTS Database,
National Plant Data Center, Baton Rouge, LA 70874-4490 USA