BenefitsRead full entry
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 potentially effective on this species.
Rhizomes and tubers form extensive networks in the soil. While most tubers are found growing in the upper 15 to 20 cm of soil, a few penetrate to a depth of 40 cm. The root system in heavy clay may extend more than a meter deep (Andrews 1940; Smith and Fick 1937). Under favorable conditions, a single tuber could produce 99 tubers in 90 days (Rao 1968). Experimental plantings of tubers set on 0.9 meter centers resulted in their nearly five-fold increase by the end of the growing season (Hauser 1962).
Tubers resist all but high temperature extremes, but seem more sensitive to lower temperatures. Germination failed in tubers held for 12 hours at 500 C. However, greater than 80% germination occurred after exposure to 400 C. Tubers exposed to temperatures of -5 0C or lower did not survive more than two hours (Ueki 1969).
Tubers and basal bulbs serve as vegetative propagules. They are carried on farm tillage implements and may be spread by erosion and running water. Severe storms may bring tubers to the surface and transport them to new areas. Such propagules may also be transported long distances with nursery stock. Even though purple nutsedge flowers abundantly, it rarely produces viable seeds. Seeds, although of little reproductive significance in the southern United States, are disseminated by wind or water, transported in mud, or carried onto fields by flooding streams or with irrigation water (Wills 1987; Holm et al. 1977).