The Weedy Nutsedges (Cyperus spp.) Outline

II.- BIOLOGY AND ECOLOGY

A.- Origin and evolution.
The generic family name Cyperaceae comes from the Greek word Kypeiros that means rush or sedge.

1.- C. esculentus.

a.-The name comes from the latin words esculent=edible, good to eat

ulentus=a suffix meaning abundance

esca=food

b.- Theophrastus (371-287 B. C.) describe its use. Growing in sandy habitats not far from the Nile river.

c.- Wall paintings in Egypt suggests tiger nuts (tubers) were important.

d.- Tiger nuts recorded in the Ebers and Hearst papyri as having medicinal properties (Darby et al. 1977).

e.- Exclusive presence in Egypt as cultivated plant.

f.- Textual evidence it was grown in ancient Assyria (Campbell Thompson, 1949).

g.- Found mostly in native habitats previous to 1950.

h.- became a troublesome weed in cultivated fields few decades ago..

i.- Increased use of selective herbicides probably helped the increased troubles caused by this weed.

j.- Spread to cultivated fields could be by implements of cultivation or by tubers attached to crop transplants.

2.- C. rotundus.

a.- Name comes from the latin word rotundo=circular, round.

b.- The plant is generally round in cross-section when viewed from above.

c.- Records from the Mycenaean Greece period. Used for perfume manufacturing.

d.- Was used by Egyptian priests.

- Tubers found in Egyptian tombs (21st to 12th centuries B. C.)

e.- In the classical world: Mentioned by Herodotus and Hippocratic doctors (5th. Century B.C.).

f.- Listed by Theophrastus among other perfume plants

g.- De materia medica.- First report of purple nutsedge acting possibly as a weed (Gunther, 1934)

h.- Still used in folk medicine in North Africa, from Morocco to Egypt, Israel, Iraq, Iran, India and the Far East (Negbi, 1992).

B.- Description and Anatomy.
1.- C. esculentus.
Herbaceous perennial weed with a spreading rhizomatous growth habit.

a.- Rhizomes.

- About 15 cm long and 0.5-1.5 mm thick.

- Covered with brown to blackish scales.

- Ending in a blackish tuber 3-8 mm in diameter.

- From sprouting tubers or from basal bulbs.

- They develop as indeterminate stems with nodes or internodes and may reach 60 cm in length with 30 internodes before differentiating at the apex to form either a tuber or basal bulb.

- Scarious, veined, scale-like leaves are found at each node.

- Buds are never found on rhizomes and thus they are incapable of producing new plants.

b.- Basal bulbs.- Formed from meristematic cells of rhizome tips.

- Short, acropetal stems with compact nodes.

- In its meristematic regions at the parenchyma cells, new rhizomes develop.

c.- Shoot.- Leaves in three ranks developed from primordia at nodes in the basal bulb.

- Leaves are as long as stems.

- 5-6 mm wide with prominent mid-vein.

- Grass-like leaves. Largest leaf-blades 10-30 cm long and 3-9 mm wide.

- Flat, scabrid on margin and major ribs

d.- Stems.- Triangular, unbranched, glabrous with 3-many crowded leaves near the base.

- 15-80 cm long and 1-5 mm thick.

e.- Inflorescence.- Golden-brown, umbelliform.

- leaf-like bracts. 3-20 cm long and 3-15 cm wide.

- Anthela consisting of one sessile and 3-10 stalked spikes on 0.5-15 cm long peduncles

- Often with 1-5 secondary (usually stalked) spikes from the base of some primary spikes.

- Spikes 1-3 cm long and 1-3 cm wide, with 4-12 spreading spikelets.

- Spikelets strongly flattened, rachilla of spikelets not disarticulating at maturity

- Scales ovate to obtuse, 2-3 mm. long, golden-brown, keeled, nerved

- Stigma 3-parted; stamens 3; 1-seeded; seeds 3-angled, ellipsoid, whitish to yellowish brown, 1.2-1.8 mm long (Haines and Lye, 1983).

f.- C. esculentus can be distinguished from other Cyperus species by the conspicuos scales on its rhizomes and by its terminal tubers. Both of this characteristics are entirely absent in the other species.

g.- General characteristics:

- Tuber shape: generally spherical

- Tuber taste: sweet, mild.

- Tuber color: tan to brown

- Tuber size:0.5 to 1 cm long

- Tuber arrangement: as single tubers

- Leaf color: light green

- Basal leaf length: longer than stem

- Leaf tip: sharply pointed

- Flower color: yellowish

- Plant height: 25 to 50 cm.

(Compiled from Doll, 1983).

2.- C. rotundus.
Erect, persistent, glabrous perennial herb.

a.- Stem.

- Triangular in section

- Somewhat swollen stem-base

- 25-80 cm long and 1-4 mm thick.

- With many crowded leaves in the basal part.

b.- Tubers.

- Variable shape.

- 1-2 cm long x 0.5-1 cm in diameter.

- White, succulent and almost round when first formed.

- Become almost black and hard at maturation.

- Accumulation of starch.

- Chains of two to four or more tubers (difference with C. esculentus).

- Tubers produced at the rhizome apex, behind the leaf primordia.

- Conical buds, covered with pointed scale leaves.

c.- Rhizomes.

- Extensive, horizontal, slender rhizomes.

- White and fleshy.

- Covered with scale leaves as when young

- Scale leaves become brown, fibrous or "wiry" when old.

- Rhizome tip is composed of successive layers of sharply pointed scale leaves

- Axillary buds do not appear on the rhizomes.

- Gives rise to underground tubers or basal bulbs, it then has the capability to produce a new plant if separated from the parent tuber.

d.- Basal bulbs.

- Arise from the meristematic cells of the rhizome apex.

- It is believed that they are formed after leaves develop from the shoot

e.- Leaves.

- Flat or enrolled, scabrid at least on margin and major ribs.

- Dark green.

- They vary from 5-20 cm in length x 2.5-7.5 mm wide.

- Largest leaf-blades 15-30 cm long and 4-8 mm wide.

- Extend from the bulb in an infolded triangular fascile.

- Aerial and subterranean vascular systems interconnections normally remains intact throughout the growing cycle.

- Waxy cuticle and no stomates in upper leaf surface.

- Lower surface: thinly cutinized with rows of parallel stomates (140-370/mm2).

- Stomates: larger than in C. esculentus. More leaf wax and chlorophyl (Le Court et al., 1981).

f.- Inflorescence.

- 3-15 cm long x 2-12 cm wide anthela.

- Solid, leafless, nodeless, triangular stalk emerging from the basal bulb.

- Umbel reddish brown to purplish

- Inflorescence bracts: 1-7, leafy, erect or spreading. The largest:3-20 cm long x 2 9 mm wide.

- Spikes: 1-5 cm long x 1.5-7.0 cm wide.

- Spikelets: 8-70 mm long x 1.3-2.0 mm wide

- Ovary entire in the center of the flower and usually sessile.

- Dark brown three-sided achene: 1.5 x 0.8 mm in size.

- Seeds have a thick and hard pericarp.

- Embryo is located at the base of the seed (Justice and Whitehead, 1946).

g.- General characteristics:

- Tuber shape: irregular shapes

- Tuber taste: bitter, strong

- Tuber color: nearly black

- Tuber size:1 to 3 cm long

- Tuber arrangement: often in chains

- Leaf color: dark green

- Basal leaf length: shorter than stem

- Leaf tip: somewhat blunt

- Flower color: purplish

- Plant height: 25 to 30 cm.

(Compiled from Doll, 1983).

a.- Found in all continents (Holm et al., 1977)

- From southernCanada, in North America, to northern Argentina in South America

- In southern Europe, and in Africa including Madagascar (Cour, 1960).

- Canada.- In native habitats and cultivated fields in Nova Scotia, New Brunswick, southern Quebec and southern Ontario (Mulligan and Junkins, 1976).

- United States.- Occurs in all states, except North Dakota (Reed and Hughes, 1970).

b.- Abundant in subtropical and temperate climates but not in tropical areas.

2.- C. rotundus.

a.- Native to the tropics, but has spread into subtropical areas too.

b.- Found in more countries than any other weed in the world.

c.- Grows from 30 oN to 35 oS latitude

- Limited by cold temperatures.

D.- Habitat.
1.- C. esculentus.

a.- In moist, poorly drained or irrigated fields.

b.- Along stream banks, roadsides and ditches.

c.- In light textured and well drained soils, particularly in annual crops.

d.- Grows well on a wide range of soil types.

- sand, sandy-loam, sandy-gravel, loam, muck, clay-loam and clay.

e.- Survive in low air and soil temperatures.

- Tuber's ability to withstand low temperatures for long periods.

- Extreme coldness of the air on the soil surface is not usually transmitted down to soil layers.

f.- In native habitats: soil is flooded in the spring. In cultivated fields: it grows in drier soils.

g.- PH from 5-7.

h.- Tubers survive freezing temperatures during winters

- Tubers:only vegetative part of the plant that overwinters.

- All other plants part are killed by frost.

2.- C. rotundus.

a.- Grows in almost every soil type, relative humidity, elevation, pH, soil moisture and soil organic matter level.

b.- It does not grow well in soils with high salts and is not shade tolerant.

c.- Found in cultivated fields, roadsides, in citrus groves, along irrigation canals and drainae ditches in plantation crops, in fencerows, at the edges of woods, and any neglected area.

a.- 34% loss in cotton yields with full season competition (Keeley and Thullen, 1975).

b.- Average of 8% in maize fields in the Central USA (Stoller, 1981)

c.- A yield loss of 8% in maize is expected for each 100 nutsedge plants/m2 (Doll, 1983).

d.- Reduction in the quality of root crops. Ex: rhizomes penetrate potato tubers.

2.- C. rotundus.

a.- Serious interference with crops.

- Compete effecticely for nutrients, water and, in the early growth stages, for light

- Invariably emerges and grows more rapidly than the crop.

- In rice crops causes yield reductions, competing for N.

- Rice yield nearly tripled in response to N fertilization, when the weed was absent (Okafor and De Datta, 1976).

b.- Potential to reduce yield is not reflected by its size.

- Tubers can compete effectively for water and nutrients with sugarcane.

- Rochecouste (1956): Purple nutsedge can mobilize and store 815 kg of ammonium sulphate, 320 kg of potash and 200 kg of superphosphate per hectarea.

c.- In maize, critical period of competition is early in the crop cycle.

- A 10-day delay between planting and the first weeding: 19% yield loss in Colombia (Cruz and Cardenas, 1974)

- 30 days of delay: 27% of the crop lost.

- Full season competition: 40% of yields reduction.

d.- Quality of root crops (sweet potatoes and cassava), tubers (potatoes and onion bulbs) is reduced (penetration to any underground structure can occur).

a.- Dried tissues can inhibit the growth and development of other plants.

b.- Tuber residues: more inhibiting to maize and soybean growth and development than foliage residues.

c.- Soybeans: more susceptible to C. esculentus residues than maize.

d.- Water extracts: inhibition Amaranthus retroflexus, Echinochloa crus-galli and Chenopodium album germination and growth.

e.- It is believed that allelopathic effect is caused by phenolic compounds.

2.- C. rotundus.

a.- It is common to find "monocultures" in moderate to heavy infestations even when no annual weed control measures were used.

b.- Exudates inhibite barley growth.

- Plantation in soil previously infested: barley, cotton, and mustard had reduced germination (Friedman and Horowitz, 1971).

- Soils incubated with pieces of tubers and rhizomes, inhibites root growth of crops.

- Barley growth was inhibited 15-25% by the residues (1-3 months from decay)..

- Accumulation of biomass in soybeans and sorghum was reduced with presence of tubers or foliage (Lucena and Doll, 1976).

G.- Account of variation.
1.- C. esculentus.

a.- Several workers have reported the presence of biotypes.

b.- Hauser, 1968:

- Two clones from Delaware and Georgia, exhibited different gross morphological characteristics. Georgia plants were taller, flowered later, produced plants located further from the parent tuber, and produced larger tubers than did plant from Delaware.

- Plants from Kemptville, Ontario grown in a greenhouse at Ottawa with plants from Thorndale, Ontario flowered earlier and had more flowers than Thorndale plants.

c.- Plants from different geographical areas have different responses to herbicides (Hauser, 1968).

- 2,4-D was ineffective in New York and Rhode Island, but partially effective in Georgia.

d- Mulligan and Junkins, 1976: North American weed is a single specie.

e.- Biotypes have differences in tuber numbers and size., flowering, seed production and leaf characteristics. Differences in allelopathic potential also exist.

- Tubers collected from eight locations in Wisconsin showed different allelopathic potential, suggesting presence of biotypes.

2.- C. rotundus.

a.- It is thought that there are ecotypes among this species.

b.- Fuentes and Doll (1976): They collected clones in four distinct climatic regions, grown under uniform conditions and they did not detect biotypes.

c.- Ranade and Burns (1925): Morphological differences to distinguish varieties.

- Glume colors noted: yellowish white, light red, coppery red and dark red with a blackish tinge.

- Colors are inherited. Not due to developmental or environmental differences.

d.- Claver (1977): Bioype from the tropical northwest ( in Argentina) and biotype from the subtropical southeast, when growing under identical conditions, have different responses in flowering, not caused by the photoperiod.

H.- Growth and development.
1.- C. esculentus.

a.- Tubers: Formed at the end of rhizomes and not in chains.

- White when first formed and gradually turns brown and finally, nearly black (at maturity).

- Formation: in late July and August until the end of the season (in the north central USA). At this time tubers have 1/4 to 1/3 of the total plant dry weight.

- Tuber emergence: soil temperatures reach 12 oC. May continue 60 days.

- One tuber: 1-3 buds usually sprout.

- If the first ones are killed, remaining buds will sprout and send out determinate rhizomes.

- First flush of sprouts consumes 60% of the food reserves. Subsequents shoots are less vigorous.

- Apical dominance of the first shoots prevents additional buds from sprouting.

- First determinate rhizome: grows and forms a primary basal bulb below the surface.

- Determinate rhizome and parent tuber may remain alive and attached to primary basal bulb for up to 12 weeks.

- Parent tuber disappears by the end of growing season.

b.- Basal bulb: Principal vegetative activity and propagation.

- Formed at the tips of rhizomes, below the soil surface (2 to 5 cm) in response to the stimulus of daylight.

- Remain below the ground.

- Contain rhizomes for leaves, rhizomes, roots and flower structures.

- Differentiation from rhizome tips is maximum in photoperiods of 16 hours of light.

c.- Rhizomes: Formed from basal bulb.

- Tip of first rhizomes turns upward and form secondary basal bulbs.

- Production of a complex system of rhizomes.

- Tuber formation occurs on others rhizomes.

- Rhizomes from basal bulb are indeterminate, they may form basal bulbs or terminate in tuber formation.

- Rhizomes from sprouting tubers are determinate and only form basal bulbs.

- Long days promote basal bulbs formation.

- Short days enhance tubers formation.

d.- Leaves: A new leaf is formed every 4 1/2 to 5 days.

- Sigmoid growth pattern.

- Growth ceases after 7 days.

-Total period of leaf growth: 24-40 days.

e.- Roots: from endodermal tissue of rhizomes, basal bulbs and tubers.

-Represent only a small portion of the total plant biomass.

2.- C. rotundus.

a.- Stablishment from seed is not common.

- Viable seeds are produced.

- Basal bulbs and new tubers: formed within 10-15 days after seed germination (Ranade and Burns, 1925).

- Claver (1977): 16 days after germination seedlings had one true leaf and a second one was developing.

- At 41 days, three leaves present and one rhizome from the basal bulb.

- After 85 days from germination tubers began to form on rhizomes.

b.- Tubers are the primary source of infestations.

- Hauser (1962): Tuber formation: six weeks after planting.

- After initial shoot emergence, tuber chains were formed after ten weeks.

- Subterranean components always weighed more than aerial parts.

- Apical dominance is related to inhibitors in tubers. Can be reduced by increased oxygen levels (Mercado, 1979) and is exhibited in two forms:

- apical bud of a single tuber always sprouts first.

- uppermost or youngest tuber in a chain exerts apical dominance over other tubers in a long chain.

- Cutting one tuber horizontally, the bud nearest the cut surface on the bottom half of the tuber sprouts first.

- Chain dominance is lost when rhizomes are severed.

c.- Basal bulb forms near the soil surface and as deep as 20 cm.

d.- Roots and rhizomes arise from basal bulb.

- Roots penetrate deeper in the soil than the rhizomes.

- Andrews (1940). Found roots 135 cm deep in a heavy soil.

- A tuber can rise to the soil surface one or two rhizomes.

- Rhizomes grow from 1 to 30 cm horizontally before tip form a new aerial shoot with another basal bulb.

- Or rhizome will remain below ground and form a tuber from which another rhizome will develop from the apical end.

- Chains of tubers are formed as deep as 50 cm in the soil.

e.- Flowering occurs from 3 to 8 weeks after emergence.

- In dense stands produces fewer flowers than in sparse stands.

I.- Effects of the environment.
1.- C. esculentus.
a.- Light.

- Photosynthetically efficient C4 plant.

- Differentiation of rhizomes tips into basal bulbs: maximum at 16 h daylight and into tubers at 8-12 h daylight.

- Tubers can be formed at any photoperiod.

- Seed germination can be inhibited by complete darkness at temperatures no optimal for germination.

- Under artificial conditions, alternating temperatures of 20 oC to 35 oC promoted maximum seed germination.

- Lower than 10 oC: detrimental to seed germination.

-Bell et al (1962): tuber sprouting was greatly reduced when soil was compacted.

-Plants grown at 100% moisture produced significantly more tubers and vegetative material than those grown at 50% moisture (Bell et al. 1962).

- Influence tuber production.

- Shoots from tubers planted in sand emerged sooner than those in sandy silt-loam, but tubers in sandy silt-loam produced more plants at the end of 6 weeks (Tumbleson and Kommendahl, 1961).

- Tubers planted in peat produced the most shoots per tuber initially and finally.

- Photosynthetically effective (C4 plant).

- Day length is a major factor influencing growth and development.

- Berger (1966): short photoperiod (10 h) enhanced flowering and high production of developed roots, rhizomes, and tubers.

- Long photoperiod (18 h): no flowering but develop of vigorous foliage.

- Wills (1969): Flowering occurred at 13 h or less of direct sunlight and no flowering occurred after 6 weeks during 14 h or more of direct sunlight.

- Total and shoot dry weight generally increases with increased photoperiod and time (Williams, 1978).

- Under 8 h photoperiod: the least total, shoot, root, rhizome and tuber dry weight production.

- Flowering occurred only at 12 h photoperiod (intermediate in flowering response to daylength).

- Under 16 h photoperiod: plants had shorter shoots than plants under 8 and 12 h photoperiods.

- Flowering is thought as a result of short photoperiods of 6-8 hours (Doll, 1983).

- Shade decreases competitiveness, however when transferred from dense shade to full sunlight after 30 days (Patterson, 1982), it recovered dramatically and produced 91% as much dry weight and 102% as much leaf area as plants kept in continuous light.

- In the shade fewer and thinner leaves are produced and formation of rhizomes and tubers are reduced

- Maximum growth: high light intensity and warm temperatures.

- Important in determining new tuber size and proportion of dry matter as new tubers.

- In a heavy soil, growth ceased when moisture content fell below 20% (Andrews, 1940).

- Grestest growth in soils at 75% of field capacity to soil saturation (Fuentes and Doll, 1976).

- Growth was 81% greater in heavy textured soils with high water levels than in dry light textured soils.

- Highest concentrations of N, P and K found in weed foliage in the light textured soils.

- Tubers do not lose viability even after 200 days under water (Ueki, 1969).

- Production of more shoots per tuber than non-flooded tubers can occur when water is removed.

- Tubers have high bound water level, low surface to mass ratio, and an endodermis-like layer inside the cortex which becomes hard and thick as tubers age, reducing water loss (Jha and Sen, 1980).

- It is adapted to drought over time, even it is a moisture loving plant

- More rhizomes terminated in tubers when N levels were low.

- 3-9 ppm N levels: no flowering but tubers are formed, at 27 ppm (Nyahoza, 1973).

- High numbers of both tubers and inflorescences at 81 and 243 ppm N (Chadwick and Obeid, 1963).

- Maximum rhizomes numbers occurred at pH of 7.0

- Normal growth at 5.5 to 7.0 but was greatly restricted in very acidic soils.

- Al-Ali et al. (1978) observed a wider pH tolerance:

- Optimal growth: pH= 3.5-7.0

- Tubers sprouted in pH=2.2-2.6 but did not survive 30 days.

- Half the tubers sprouted in pH=7.6 and survived 30 days.

- pH=8.6-9.0: 15% of the tubers survived.

- Adapted to a wide range of soil acidities, as long as minor element imbalances do not occur.

J.- Flowering.
1.- C. esculentus.

a.- First sign of flowering: appearance of a hollow, triangular foliar tube, formed by the two youngest leaves growing as a single unit, through which the scape must elongate.

b.- Scape extends, floral structures in the meristems in axils of elongating involucral leaves begin to differentiate.

c.- Effect of photoperiod in flowering.

- It occurs in photoperiods of 12-14 hours.

d.- Reports about flowering is variable as it does not occur in all populations annually.

e.- In the north central USA: occurs in photoperiods greater than 14 hours.

f.- In Canada, it occurs between early July and September and is thought to be controlled more by temperature than photoperiod.

g.- Flowering can occur under 30-60% of full sunlight.

h.- This process competes with other plant processes, but is not considered of high significance since the plant rarely propagates by seed.

i.- Flowers: perfect, wind pollinated and self-incompatible.

j.- In denser stands, flowering is reduced.

a.- Flowering is somewhat variable.

b.- Generally occurs in photoperiods of 8-13 h.

c.- Flowering does not begin until the plant has seven leaves and is maximum when nine leaves are present.

d.- Flowering is greater during periods of high humidity.

a.-Stablishment by seed in the field has not been documented, but it can occur.

b.- Iimportance of seed in life cycle has not been clearly defined.

- Contradictory evidence and opinions in the literature.

- Mulligan and Junkins (1975).- No evidence that seed played a role in reproduction in cultivated areas.

- Growers of irrigated cotton in California believed that it was the main agent of dissemination.

c.- It is believed that seed are not of major importance in cultivated areas because seedlings lack the vigor to survive these conditions.

- The number of successful seedlings in the field depends upon conditions that affect seed longevity, germination and seedling survival.

d.- Flowers do not always produce seed.

e.- Weather conditions and genetics influence the degree of seed production.

- Germination of seed is affected most by temperature.

- Light and moisture conditions play a role too.

- Although seeds germinate readily, survival of seedlings is extremely limited.

f.- Yellow nutsedge can produce large numbers of seed: 605 million/ha in Massachusetts (Hill et al., 1963) and over 100 million/ha in Zimbabwe (Lapham, 1985).

-There is a potential to reproduce prolifically from seed.

g.- As many as 1,520 seed/inflorescence with a 76% germination have been reported.

h.- Seed weight: 0.13-0.31 mg.

i.- Viable seed is formed about two weeks after anthesis.

-Viability of mature seed ranges from less than 5% to greater than 40%.

j.- Best germination: 38/32 oC day/night temperature, especially with light.

- At alternating day/night temperatures of 35/20 oC: 59% seeds germinated in continuous light and 46% in complete darkness.

- At 30/20 oC, 36% germinated in light and 1.5% did in darkness (Lapham and Drennan, 1990).

k.- Bell and Larssen (1960): Germinations reported at many locations:

- New York: 84-89%.

- Rhode Island: 61-76%

- Delaware: 58%

- Maine: 28%

h- Some seeds are dormant, whereas others are semi-dormant to non-dormant at maturity.

- First 6 months after sowing: proportion of innately dormant seed decreased rapidly at all depths (Lapham and Drennan, 1990).

- No differences in the proportions of innately dormant seed at different depths.

- Justice and Whitehead (1946): 79% of seed had germinated by 4 months after harvest.

- Germination can be enhanced with:

- Storage at room temperature or 4 oC.

- Scarification with sulphuric acid.

- Treatment with potassium nitrate.

i.- Only seeds near the soil surface are capable to emerge.

2.- C. rotundus.

a.- Seed germination occurs often, but the infestations rarely if ever result from seed germination.

b.- Germination is seldom higher than 15% and viability is usually maintained for several years.

c.- Most seedlings emerge from 1 to 1.5 cm and up to 4,000 tubers/m2 if they stablished for 141 days.

d.- Seed production per inflorescence varies from 170 to 260.

e.- Germination is stimulated by washing with water, heating and acid scarification.

L.- Tuber development, dormancy and survival.
1.- C. esculentus.

a.- Tuber diameter: 3-11 mm

b.- Tuber weight: 70-710 mg

c.- Shading: reduces tuber production.

d.- Number of tuber produced is directly proportional to the amount of light received.

e.- Important in the stablishment and spread of yellow nutsedge.

f.- They are in the top 15 cm of the soil, rarely found below 30 cm.

g.- Hard, though lignified epidermal layer, well developed buds, a vascular system and root

h.- Changes associated with tuber development:

- Progressive shortening of internodes of an indeterminate rhizome.

- Increase in rhizome diameter.

- Starch accumulation in the cells.

- Production of numerous scale leaves by the meristem.

i.- Buds: In the axils of the scale leaves that form a cone at the tip of the tuber.

j.- Overwintering tubers: hard, oblong, slightly flattened. 0.2-1.5 cm long.

k.- After they are formed, they are dormant (summer and autumn) and usually sprout the following spring.

l.- Dormancy is broken in acropetal order, starting with the oldest bud.

m.- Tuber sprouting: increased by:

- Washing tubers in cold water for 24 hours.

- Storage at 3 to 6 oC for 30 days or longer.

- Tillage.

- Scraping black tubers with sand paper or gibberellic acid.

- Treatment with hydrogen peroxide.

n.- Basal portion inhibits the sprouting of buds at the apical end.

- If the basal half is detached from the apical, buds in the apical end break dormancy and sprout.

- Emergence varies with soil texture. Usually satisfactory down to 8-15 cm in most soils.

o.- Tubers near the soil surface in temperate climates are killed by freezing temperatures.

p.- In Illinois, the greatest viability and emergence of tubers was at 10.2 cm.

q.- In the field, tubers have survived temperatures around -20 oC

r.- Tubers from South Africa: higher survival rate at 22 oC than at 4 oC.

s.- Heavily infested fields may have 25-80 million tubers/ha

- 18 ton/ha of tubers to 45 cm deep in an infested soil (Tumbleson and Kommendahl, 1961)

- Tuber population: 10,000,000/ha in one season without control in a maize field (Stoller et al., 1979).

- Simkins and Doll (1980) reported a tuber population of 88,000,000/ha in maize and 78,000,000/ha in soybeans.

t.- Few tubers survive more than three years.

u.- Tuber longevity: dependent on tuber depth, soil moisture and temperature.

v.- Tubers are the only portion of the plant that overwinter.

- All above-ground parts, basal bulbs, fibrous roots and rhizomes are destroyed by winter conditions.

- Unsprouted tubers may be viable as long as 3 1/2 years after they are produced.

- Few survive over two winters.

2.- C. rotundus.

a.- Apical dominance controls tuber sprouting.

b.- Zandstra and Nishimoto (1977): younger tuber chains were less dormant than older chains.

- Separation of tubers from a 6-week old plant: 74% sprouting,

- 53% of tuber sprouting when they came from a 12-week old plants.

c.- Horowitz (1972): Tubers produced anytime during the year sprouted readily (76-100%)

d.- No new shoots produced by the parent tuber after a rhizome has reached the soil surface and a shoot is formed.

e.- Parent tubers do not descompose. If severed from plant can give rise to new rhizomes

f.- Most tubers (80-90%) formed in the top 15 cm of soil, few are found below 30 cm and almost never below 45 cm.

g.- If placed as deep as 60 cm, some tubers may emerge, but not if placed at 90 cm.

h.- Tuber formation approximates one tuber per day per plant for the first 90 to 140 days.

i.- Horowitz (1972): A single tuber planted in the field can spread 90 cm in two months and the end of two seasons averaged an increase in area of 2.8 m2 per month.

j.- Rodriguez and Rainiero (1983): 3,847 shoots produced by one tuber in six months.

k.- Hauser (1972): Single tubers spaced at 90 cm yielded the equivalent of 11,000,000 tubers and bulbs and 7,700,000 shoots/ha in one season.

l.- Tuber production cycles with the temperature and rainfall patterns.

m.- Sprouting and tuber growth slow in temperatures below 20 oC and peaked at mean temperature between 25-31 oC.

n.- After emergence, no tubers are formed during the first four weeks but basal bulbs increase five-fold.

o.- Sprouting occurs between temperatures 0f 10 and 45 oC, with 30-35 oC being optimum.

p.- Tubers can be killed by desiccation. They dry quickly if detached from their rhizome and root system (Holm et al. 1977).

q.- Upon maturity, tubers contain approximately 50% moisture, if it falls to 15% tuers are killed (it requires at least 4 and up to 14 days to do it).

M.- Population dynamics.
1.- C. esculentus.

a.- Usually confined to habitats recently disturbed.

b.- Native plant along the margin of rivers, streams and lakes, and in bog and marshes

- Native habitats are usually flooded in the spring and there is little competition from other plants early in the growing season.

c.- Grows also as a weed in cornfields, oats, gardens, soybeans and vegetable crops.

d.- In cultivated fields is associated with a wide variety of colonizing weeds.

e.- Appears to compete poorly with other weeds.

f.- When other weeds are controlled by herbicides, there is a rapid increase in the abundance of yellow nutsedge.

g.- Mulligan and Junkins (1976): At Kemptville:

- Overwintering tubers sprouted in mid-May, and by June 1. Few small white tubers were produced.

- On 8 July 10% of the plants were flowered and by 17 July about 50%.

- Some indeterminate rhizomes were 40 cm long but there were very few new tubers. Tuber production did not increase until after mid-August when the formation of secondary leafy plants ceased.

- On 26 August about 90% of the leafy shoots had flowered or flowers buds and some mature new tubers appeared.

- Plants often behave very differently at various locations.

2.- C. rotundus.

a.- Competition with C. esculentus: reduction in yield and number of shoots, tubers and inflorescences of C. esculentus,

- After four months of competition, both can persist and reproduce (Williams, 1983).

b.- If left indisturbed in mixed weed populations, Cynodon dactylon and Artemisia vulgaris will suppress it.

N.- Control.
1.- Cultural:

a.- Selection of fast growing crop. Competition from nutsedges ceases when shading.

b.- Use of narrowest row space for crop.

c.- Use of relatively high crop densities.

d.- Good fertilization

e.- Crop rotation

f.- Planting of permanent crops

2.- Mechanical:

a.- Cultivation or hand holing before they are stablished.

b.- Fallowing and tillage, but cost is high in time and energy.

c.- Repeated mechanical disturbance to desiccate tubers

3.- Chemical:

a.- Control is not completely successful.

b.- 2,4-D to control C. rotundus but not C. esculentus

- No effects on tubers

c.- Thiocarbamates.

- EPTC+

- Butylate+

- Vernolate

d.- Organo-arsenicals

- DSMA

- MSMA

e.- Acetanalides.

- Alachlor

- Metolachlor

f.- Triazines

g.- Bentazon

h.- Glyphosate

i.- Growth regulators

j.- Uracils.

4.- Biological control

a.- Insects: Bactra veturana

b.- Pathogens: Puccinia canaliculata

5.- Integrated control.

O.- Agricultural and Economic importance.

a.- Both species causes yield reductions.

b.- Cannot be erradicated by present control methods

c.- Wide range of crops affected

d.- Reduction in crop quality. More important when the commercial product is an underground structure

e.- Increases production costs due to increased cultivation and handweeding.

f.- Host for two nematode species that are pathogens in some crops.

- Meloidogyne sp

- Rotylenchus similis

g.- C. rotundus: Alternate host of fungal pathogens.

- Fusarium sp.

- Puccinia canaliculata

- Abaca mosaic virus

h.- C. esculentus: troublesome in irrigated areas, because can tolerate high moisture levels.

2.- Beneficial:

a.- Chufa tubers (C. esculentus) used to produce "horchata de chufa" (a beverage).

b.- Roasted tubers used as "earth almonds"

c.- Tubers and vegetation used as forage crop.

d.- Ground tubers: substitute for coffee

e.- Tubers: Production of vegetable oil and cellulose.

f.- In China: It has been used traditionally for medicinal purposes.