3.3 Growth and Development
Rhizomes and tubers of purple nutsedge form extensive networks in the soil.
While most tubers are found growing in the upper 15 to 20 cm,
a few penetrate to a depth of 40 cm.
The root system in heavy clay may extend more than 1-m deep. Under
favorable conditions, a single tuber could produce
99 tubers in 90 days. Experimental planting of tubers set on 0.9-m
centers resulted in their nearly five-fold increase
by the end of the growing season.
Tubers of purple nutsedge resist temperature extremes,
but seem more sensitive to lower temperatures.
Germination failed in tubers held for 12 hours at 50oC.
However, greater than 80% germination
occurred after exposure to 40oC.
Tubers exposed to temperatures of -5oC
did not survive more than 2 hours.
Tubers and basal buds 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 are disseminated by wind or water, transported in mud, or carried
onto fields by flooding streams or with irrigation
Purple nutsedge possesses the C4
photosynthetic apparatus, which is an adaptation to assimilating
CO2 at higher
temperature 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 from around the vascular bundles serve to compartmentalize
the photosynthetic events.
Tubers and rhizome production are important factors in the purple nutsedge's 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 capable of surviving extreme environmental conditions.
Tubers make the plant difficult to control, because only translocated
herbicides are potentially effective on this species.
Besides their competition for resources, 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 kg of subterranean plant material per hectare.
Under experimental conditions, barley yield
was reduced by 15 to 25% by C. rotundus residues in the soil.
Tubers of purple nutsedge tolarate high temperatures, but not freezing.
They germinate when soil temperatures remain above 15oC.
Typically only one tuber in a chain germinates, unless the chain is severed. Low oxygen and high carbon dioxide levels appear to
promote tuber dormancy. Tuber dormancy is high in undisturbed soils and deeper soil levels.
Tubers can remain dormant for long periods and can become dormant after sprouting. Tuber dormancy often increases with age. New tubers
are initiated when flowers develop, often about 4-8 weeks after shoots emerge. Tubers planted at a depth of 90 cm are usually
unable to produce aerial shoots.
Tubers desiccate quickly when detached from the rhizome-root system under dry conditions and can
survive flooded soils for at least 200 days. Tuber longevity is variable and depends on environmental conditions. In most cases, tubers
survive about 3-4 years, but under certain conditions, they can remain viable for up to 10 years or more. Seedling survival is typically low.
Purple nutsedge has been called the world's worst weed. This is a befitting designation for a species known from more countries (at least 92)
than any other weed and that infests at least 52 different crops worldwide. It grows in all types of soils and can survive with the
highest temperature 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 nature, 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
3.5 Economic Importance
Cyperus rotundus, reportedly originating in China, is used as a carminative and energy and hormone regulating herb in Traditional
Chinese medicine. Purple nutsedge has also been used 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.
Extracts and compounds from purple nutsedge have medicinal properties such as reduction of fever, inflammation, and pain.
The literature contains numerous references to the use of the roots of this plant for essential oils and its seeds for food products. Tuber extracts
may reduce nausea and act as a muscle relaxant.
3.6 Chemical Control
There are no herbicides registered for use on all vegetables that will control purple nutsedge.
While there herbicides that can be used safely to control purple nutsedge in lawns, these herbicides
should not be used on vegetables, unless so specified on the label. Herbicides such as Image, Manage, or MSMA
can be used to successfully control purple nutsedge in the lawn; however, these herbicides will severely injure
or kill most vegatables or may result in herbicide residue in the produce.
The chemical control of purple nutsedge is described in the following tables.