Cyperus rotundus

Scientific Name Cyperus rotundus L.
Common Names English: Cocograss, purple nutsedge, German: Nussgras, Rundes Cypergras, French: Souchet rond; Spanish: Castañuela, Portuguese: Junça, tiririca-comum
Description Highly variable perennial sedge with fibrous roots. Rhizomes are wiry, dark and persistent, connecting a network of daughter shoots and tubers. The tubers are dark brown to black, irregularly shaped and 1-2 cm (0.39 - 0.78 inch) long when fully grown. Each tuber has an apical bud and several lateral buds.

Descriptions

Characteristic Features

Can be distinguished from other sedge weeds by its wiry rhizomes linking a network of tubers. Purplish-brown spikelets and leaf-tips coming to an abruptly acute tip.

Young Plant

Seedling are not often found, seedlings are grass-like and later develop 3-sided, triangular base.

Stems

Flowering stems are erect, up to 60 cm (23.62 inch) tall, 3-sided, smooth with swollen bases (basal bulbs).

Leaves

The leaves have a distinct midrib, are linear, usually shorter than the flowering stem, up to 7 mm (0.27 inch) wide and emerge from a sheath around the shoot base.

Propagatio Organs

Flowers

The inflorescence is a terminal, open umbel-like cluster subtended by several leafy bracts. Several unequal rays, 2-6 cm (0.78 - 2.36 inch) long, support 3-8 reddish-brown to purplish-brown, flattened spikelets, 1-2 cm (0.39 - 0.78 inch) long and 2 mm (0.078 inch) wide, each with up to 30 glumes, 3.5-4 mm (0.13 - 0.15 inch) long.

Flowering Period

Summer until autumn.

Fruit

The fruit (often, but erroneously, known as the seed) is a 3-angled achene, 1.5 mm (0.059 inch) long, dark brown or black.

Seeds

Germination predominantly in spring and summer.

Viability Of Seeds

Most seeds of C. rotundus are not viable. Dispersal by seed is generally regarded as being unimportant.

Propagation

Cyperus rotundus mainly reproduces by rhizomes and tubers. Hundreds of tubers can be produced in one season at the tips of the rhizome. Tubers require a chilling period to break dormancy and produce a primary basal bulb 1-2 cm (0.39 - 0.78 inch) beneath the soil surface.

Occurrence

Habitat

Cultivated fields, waste areas, roadsides, pastures, and natural areas.

Soil

Almost every soil type, elevation, humidity and soil with preference to wet light soils.

Additional Crop Information

A weed in more than 52 crops, including vegetables and ornamentals.

Agricultural Importance

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 rapidly growing plant can quickly form dense colonies due to its ability to produce an extensive system of rhizomes and tubers: The typical life cycle of C. rotundus starts with growth of the apical bud of a tuber. As the tuber shoot extends, it swells to form a basal bulb, usually near the soil surface, from which an aerial shoot and roots are produced. Up to 3 or 4 rhizomes develop from each basal bulb, extending 5-30 cm (1.97 - 11.81 inch) before turning upward to form a further basal bulb, and in more mature plants, these rhizomes may form dormant tubers, without any aerial shoot. Chains of rhizomes and tubers become an extensive underground network. Tuber dormancy may last for at least 7 years, cultivation stimulates the growth of C. rotundus. As many as 600 plants have been produced in a single year from a single tuber. 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.
Many studies document reduced yields in sugar cane, corn, cotton, rice, vegetables, and numerous other crops. 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%. Purple nutsedge may produce up to 40,000 kilograms of subterranean plant material per hectare (35,274 pounds/a.), containing mostly starch.
Under natural conditions, a population of C. rotundus extends its boundary by a few metres in a year. Nutsedge is very difficult to control once it is established. Other important representatives of this genus are Cyperus esculentus and Cyperus iria.

Control

Integrated Crop Management

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 desiccated beyond recovery after 4 days.
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%. 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.

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