Cyperus rotundus (purple nutsedge) is a smooth, erect and perennial weed with an extensive subterranean tuber system (Hauser 1962, in Quayyum et al. 2000; Singh Pandey & Singh 2009). It usually attains a height of about 30 cm (Quayyum et al. 2000). Purple nutsedge appears grass like, but its stems are triangular in cross-section. It has fibrous roots that branch prolifically, rhizomes, tubers, bulbs, and inflorescences that consist of irregular compound umbels. Its leaves are mostly basal and linear in shape with a prominent mid-rib (Ministry of Agriculture and Lands of British Columbia 2007, in Rogers et al. 2008).

The impact of climate change on invasive species is a fascinating aspect of invasion biology. Rogers and colleagues (2008) tested the effects of a rise in atmospheric CO2 on purple nutsedge in controlled studies. Purple nutsedge exposed to elevated CO2 had greater total dry weight, leaf area, root length and numbers of tubers and tended to increase allocation belowground, which led to greater root-to-shoot ratio (R:S). These findings suggest that purple nutsedge may be more invasive in a future high-CO2 world (Rogers et al. 2008), however, the experiment did not account for the competitive impact of other biota.

Tuber Sprouting (Stoller & Sweet 1987): In purple nutsedge, tuberization can begin within 17 days after shoot emergence (Hammerton 1974, in Stoller & Sweet 1987), but dormant tubers are not found until 6 to 8 weeks after sprouting (Hauser 1962, in Stoller & Sweet 1987); this is followed by chain formation 10 weeks after shoot emergence (Hauser 1962b, in Bangarwa et al. 2008). Tuberization in purple nutsedge may be a response to excess carbohydrate, regulated by growth substances, photoperiod and temperature (Garg Bendixen & Anderson 1967, Hammerton 1975, in Stoller & Sweet 1987). A single purple nutsedge tuber can produce 100 tubers when allowed to grow for 12 weeks (Rao 1968, in Bangarwa et al. 2008). A patch originating from a single tuber can expand up to 5.5 m2 and produce 750 shoots within 6 months (Webster 2005, in Bangarwa et al. 2008). \n\n
Tubers lie dormant in the soil until stimulated to sprout. When a tuber sprouts, one or more rhizomes elongate vertically from tuber buds. Roots radiate horizontally from the rhizome as it grows toward the soil surface. The rhizome tip at the soil surface is exposed to sunlight and diurnal temperature fluctuations which are the principal factors that stimulate the basal bulb to form on the rhizome under the soil surface (Stoller & Woolley 1983, in Stoller & Sweet 1987). These rhizome tips are strong and sharp and can penetrate hard substrates, so mulching is an ineffective control. The rhizome extends mostly by internode elongation until the basal bulb is initiated. Basal bulbs consist of a section of stem (rhizome) with compacted internodes containing meristems for roots, secondary rhizomes, leaves, and the flower stalk. Parent tubers remain attached to the plant throughout the season, and the plant may derive food from tubers in times of stress (Hammerton, 1974, Stoller, Nema & Bhan 1972, in Stoller & Sweet 1987).\n\n
Vegetative Development: Several weeks after the primary shoot emerges, secondary rhizomes radiate horizontally from the basal bulb. In the early growth stages, the rhizome tips turn upward, differentiating into secondary basal bulbs similar to the primary basal bulb. Secondary bulbs produce shoots, rhizomes, and flower stalks as described for primary bulbs; and subsequent development of tertiary and higher order bulbs forms the complex system of subterranean, vegetative growth.\n\n
Flowering: Flowering is erratic among yellow and purple nutsedge populations. Many populations of yellow and purple nutsedge do not flower after growth for a cropping season, but tubers always are produced when these weeds grow for that length of time.

Several chemical compounds have been isolated from world's worst weed Cyperus rotundus (Jeong et al. 2000, Sonwa & Konig 2001) and some of these chemicals possess medicinal properties and are used in Latin America, China and elsewhere (Ellison & Barreto 2004; Singh et al. 1970, Gupta et al. 1971, Weenen et al. 1990, Hamada 1993, Thebtaranonth et al. 1995, Makino et al. 2003, in Sharma & Gupta 2007). For example, decoctions of the plant in Brazil are used for their anti-infective and anti-inflammatory properties (Cristina et al. 2005). Various preparations of C. rotundus have been used for centuries in perfumes, spices and traditional medicines in India, China, Arab and Africa (Sharma & Gupta 2007). C. rotundus is also an important ingredient of anti-aging Ayurvedic neutraceutical Chyavanprash (Sharma & Gupta 2007). Pigs eat its tubers; however it makes a poor fodder species; it is also reportedly used as a soil stabilizer (Ellison & Barreto 2004).

Cyperus rotundus is found in cultivated fields, farmlands, neglected areas, wastelands, grasslands, at the edges of forests, and on roadsides, sandy or gravelly shores, riverbanks and irrigation canal banks (Holm et al. 1977, Wiggins & Porter 1971, in PIER 1999). It is prevalent in disturbed areas and lawns/turf. It is a major agricultural and garden weed but only a minor weed in other respects (Swarbrick 1997, in PIER 1999). \n
Purple nutsedge grows well in almost every soil type, over a wide range of soil moisture, pH and elevation. It is encouraged by frequent cultivation and grows best in moist fertile soils (Swarbrick 1997, in PIER 1999). In cool or waterlogged soils it grows slower, flowers little and produces fewer tubers (Holm et al. 1977, in PIER 1999). It is less tolerant of low temperatures and shaded areas than yellow nutsedge (Santos et al. 1997, in Rogers et al. 2008). Purple nutsedge is relatively sensitive to cold and is restricted to latitudes where the average minimum air temperature for January is higher than -1°C (Bendixen & Nandihalli 1987).\n
Bendixen & Nandihalli (1987) reported that purple nutsedge grows best where soil moisture is high, such as in upland rice and sugarcane culture and consequently is not an important weed of arid regions, except on irrigated land (Bendixen & Nandihalli 1987). Travlos and colleagues (2009), however, claim that purple nutsedge is one of the most serious weed problems of the arid and semiarid environments. Moreover, C. rotundus is one of the most common weeds of the secondary succession occurring in abandoned and dry fields of arid environments (El-Sheikh 2005, in Travlos et al. 2009). Greece is among the countries with the highest percent winter survival of purple nutsedge (Wills, 1998, in Travlos et al. 2009) making it even more difficult to control.

Seed Biology: Purple nutsedge is a perennial which rarely reproduces by seed (Thullen & Keeley 1979, in Wills 1987). Purple and yellow nutsedges have been documented to produce achenes (an achene is a small dry fruit with one seed) from aerial inflorescences; however, there are low rates of viability for purple nutsedge achenes (less than 5%), whereas yellow nutsedge achenes have 50 to 90% germination (Justice and Whitehead 1946, in Webster et al. 2008). Evidence is lacking that seeds play a significant role in propagation, especially in cultivated fields (Mulligan & Junkins 1976, Stoller 1981, in Stoller & Sweet 1987). Light does not stimulate germination of seedlings (Bell et al. 1962, in Stoller & Sweet 1987).\n\n
Tuber Biology: The aggressiveness of purple nutsedge is associated primarily with its asexual means of reproduction by underground tubers (Benedixen & Nandihalli 1987, Stoller & Sweet 1987, in Bangarwa et al. 2008). The tubers serve as perenniating organs by storing carbohydrates in a continuous reproductive cycle (Anderson 1999, Stoller & Weber 1975, in Bangarwa et al. 2008). Purple nutsedge produces a complex underground system of basal bulbs, rhizomes, and tubers (Stoller & Sweet 1987); rhizomes are initially white and fleshy with scale leaves, later becoming woody or wiry (Wills 1987); tubers are recognized as the primary dispersal unit for both species, so the literature abounds with reports on tuber biology (Stoller & Sweet 1987). \n\n
Tuber formation begins from 4 to 6 weeks after seedling emergence; many authors report that more than 95% of purple and yellow nutsedge tubers usually are formed in the upper 45 cm of and in most soils, more than 80% of tubers occur in the upper 15 cm (Stoller & Sweet 1987). When purple and yellow nutsedge are cultured in fields without interference from other plants, they produce an estimated 10 to 30 million tubers per ha in a season (Hauser 1962, Horowitz 1972, in Stoller & Sweet 1987). Both purple and yellow nutsedge tuber longevity is a function of tuber depth in the soil; tuber survival time increases as its depth in the soil increases (Stoller 1981, in Stoller & Sweet 1987). Yellow nutsedge tubers had a half-life of 4 and 6 months at 10 and 20 cm, respectively, in a non- crop environment in Illinois (Stoller & Wax 1973, in Stoller & Sweet 1987). Desiccation and temperature extremes can kill both yellow and purple nutsedge tubers (Stoller & Sweet 1987).

Tubers are also transported intentionally by food fadists and for animal feed such as chufa (Bendixen & Nandihalli 1987).Nutsedge tubers are known to develop in potato (Solarum tuberosum) tubers and other commercial root crops. Nutsedge thus is distributed with these foods and seed stocks. Nutsedge tubers also may contaminate peanut (Arachis hypogaea) during harvest and shipment. Tubers and seeds might contaminate commercial seeds and feeds and be distributed widely (Bendixen & Nandihalli 1987).Entire plants, including rhizomes and tubers, may have been used as shipping ballast then discarded after use (Bendixen & Nandihalli 1987).

For a detailed account of the impacts of Cyperus rotundus please read: Cyperus rotundus (Purple Nutsedge) Impacts Information. The information in this document is summarised below.

For a detailed account of the managment of Cyperus rotundus please read: Cyperus rotundus (Purple Nutsedge) Management Information. The information in this document is summarised below.\n\nIn agricultural fields, both purple and yellow nutsedge species reproduce primarily by underground tubers (Wills 1987). Management of nutsedges should focus on depleting tuber reserves and suppressing tuber multiplication (Bangarwa et al. 2008). \n\n\r\n

Preventative Measures: \nA Risk assessment of Cyperus rotundus for the Pacific region was prepared by Pacific Island Ecosystems at Risk (PIER); the result is a score of 13, meaning the species is likely to be of high risk in the Pacific.\r\n\n\n

Manual Control: \nApproximately 95% of purple nutsedge tubers are confined to the top 12 cm of soil (Siriwardana and Nishimoto 1987, in Bangarwa et al. 2008), making shallow tillage an effective method of reducing tuber multiplication. Tillage should be done at frequent intervals (eg: three weekly) (Benedixen and Stroube 1977, McGiffen et al. 1997, in Bangarwa et al. 2008).\r\n

\nPhysical control:\nNutsedges are capable of penetrating mulch with a thickness of four times that currently used in commercial vegetable production (Henson and Little 1969, in Webster 2005a). Plastic mulches are used in commercial vegetable gardens for suppressing weeds by providing a physical barrier (Bangarwa et al. 2008). Soil solarization, a method of increasing soil temperature using polyethylene mulch, has proved effective against many weeds when using clear film (Horowitz et al. 1983, in Bangarwa et al. 2008).\r\n\n\n

Chemical Control: \nGlyphosate and paraquat are commonly used nonselective herbicides for controlling weeds in vegetable rows, especially those systems with mulch-covered beds. Glyphosate is translocated through chains of purple nutsedge tubers, which reduces tuber viability and production (Doll and Piedrahita 1982; Zandstra et al. 1974, in Webster et al. 2008). \n\r\n

Biological Control: \nThe taxonomic isolation of the species from crop plants of importance makes it an ideal target for biocontrol (Ellison & Barreto 2004). Most of the biological control work undertaken so far has involved insect natural enemies with little success (Julien and Griffiths 1998, in Ellison & Barreto 2004). The mycoherbicide Dactylaria higginsii is a biological control fungus against purple nutsedge; repeated applications of D. higginsii provided 90% purple nutsedge control (Kadir et al. 2000, in Yandoc et al. 2006). \n\r\n

Use of Allelopathic Plants: \nThe use of allelopathic plants for weed management is an important tool in organic production systems and is gaining importance in the absence of synthetic fumigants. Plants belonging to the Brassicaceae family are known to exhibit allelopathic weed suppression (Boydston & Hang 1995, Krishnan et al. 1997, Vaughn & Boydston 1997, in Bangarwa et al. 2008). Turnip is a glucosinolate-producing Brassicaceae that has been used for weed suppression in bell pepper (Norsworthy et al. 2007). \n\n\r\n

Integrated Management:\nMethyl bromide has been a critical component nutsedge management (Julian et al. 1998, Ragsdale & Wheeler 1995, Schneider et al. 2003, in Webster 2005a). However, the use of methyl bromide as a pre-plant pest management tool was (scheduled to be) abolished in 2005 (Webster 2005b). This increases the complexity of pest management. Future pest management systems will need to incorporate a combination of tactics to manage nutsedges in crop production (Cardina et al. 1999, Patterson 1998, in Webster 2005a).