Cyperus rotundus L. - CYPERACEAE - Monocotyledon

Common name : purple nutsedge, nutgrass.

Botany Biology Phenology Ecology Distribution Agricultural importance Cultural control Biological control Chemical control

Botany :

Description :

Terrestrial, perennial, tufted to prostrate herb, rooting at nodes. Roots fibrous, white or brown. Stems triangular, solid, glabrous. Stipules absent. Leaves simple, not lobed or divided, alternate spiral, sessile, linear, more than 2 cm long/wide, margin entire, apex acute, base clasping, parallel-veined. Leaf sheath present, triangular in cross section. Flowers bisexual, grouped together in a terminal umbel, sessile, red, purple or brown, petals absent. Fruit a nut.

Biology :

Purple nutsedge reproduces by seeds and tubers. The plant spread by extensive, horizontal, slender network of tubers which are white, fleshy and covered with scale leaves when young, becoming brown, fibrous when old; this scales have axillary buds that form new plants with tubers which continue to proliferate, forming tuber chains that extend to a considerable depth in the soil.
This propagation may be favoured during cultivation as they readily break off from the connecting rhizomes. The subterranean network of rhizomes produces tubers at intervals and those tubers near the surface give rise to aerial shoots. The tubers have an extensive root system that may reach deeply into the soil.
Dissemination by seeds is very weak.

Phenology :

Flowering and fruiting throughout the year.

Ecology :

Purple nutsedge has been reported from more countries, regions and localities than any other weed in the world. It is found in all soil types and from sea level to high-mountain altitudes. It grows in wet but well drained soils and also in dry soils or climates. It is sensitive to shading, with markedly reduces tuber production, leaf area index and dry matter production. It prefers sunny or lightly shaded localities in crops.

Distribution :

Pantropical.

Agricultural importance :

Cyperus rotundus reported to be a weed in 52 crops in 92 countries. It is found in cultivated fields, on road-sides, in neglected areas and the edges of woods, and it may cover the bank of irrigation canals and streams. It may be a serious problem in paddy rice in which the soil is puddle. In seasons of low water supply, when padding cannot be done thoroughly or when the water supply fails after the rice has been transplanted, the nutsedge growing in the drying soil may choke the crop. The tubers are moved in mud on the feet of men and animals and by being caught on machinery. They are also brought into new areas when streams flood after storms, and they are distributed in surface irrigation water.

Cultural control :

Being sensitive to shading, C. rotundus can be controlled by narrow row spacing and high plant density of crops to provide rapid shading of the soil surface. In traditional rice-growing areas in India C. rotundus is controlled using pigs. Usually, the pigs are fed with vegetable waste and allowed to forage for tubers in wastelands. Because the tubers are succulent and sweet, pigs are fond of them. They can easily remove the tubers even if the soil is hard. Usually, the field is soaked with water and puddle well and then the pigs are introduced. An animal can collect 2-4 kg of tubers in one day and 60-75 animals can remove the tubers from 1 ha in one day.

Biological control :

The tortricid Bactra verutana has been evaluated for efficacy as a biological control agent for C. rotundus. Regardless of the stage of the moth upon release, the degree of control depended on the age and condition of the plant. Rates of infestation were high only when a majority of the shoots were 10-21 days old and growing vigorously.

Chemical control :

C. rotundus is difficult to eradicate, but control is most effective when herbicide use is integrated with mechanical weeding. The tuber population can be reduced by repeated application of 2_4-D and cultivation. Five 2_4-D applications at 30 days intervals followed by soil disturbance reduced tuber population by 86%. This can only be done successfully in fallows. In rice crops, almost complete control can be achieved using herbicide combinations such as pre-plant application of 2 kg of glyphosate, followed by 2_4-D at 1 kg ha-1 at 20 days after sowing.

References :
-Le Bourgeois T., Jeuffrault E., Grard P., Carrara A. 2001. AdvenRun V.1.0. Les principales mauvaises herbes de La Réunion. CD-ROM. Cirad, SPV. France.
-Holm L. G., Plucknett D. L., Pancho J. V., Herberger J. P. 1991. The world’s worst weeds. Distribution and Biology. East-West Center by the University Press. Hawaii.
-Galinato M., Moody K., Piggin C. M. 1999. Upland rice weeds of South and Southeast Asia. IRRI. Philippines.
-Radanachaless T., Maxwell J. F. 1994. Weeds of soybean fields in Thailand. Multiple Cropping Center Publications. Thailand.

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