94 Proceedings of the First International Weed Control Congress, Melbourne 1992

Mechanisms of establishment and spreading of Cyperus rotundus - the worst weed of warm regions

M. Horowitz esculentus L.(yellow nutsedge), a related perennial infesting warm and temperate zones. Department of Ornamental Horticulture, In the text, C. rotundus and C. esculentus are Agricultural Research Organization, The Volcani designated by CR and CE, respectively. Center, P.0.6 Bet Dagan, 50250 Israel Establishment and development. Summary In most cases, an infestation of nutsedge starts Establishment of Cyperus rotundus is rapid with a tuber. The tuber sprouts and forms roots and its spatial expansion is continuous and a rhizome which extends vertically and under a wide range of moisture and tem- develops an aerial shoot with a swelling perature conditions; minimum temperature (`basal bulb') at its base. Subsequently, is 20 °C for sprouting and growth, and 0 °C rhizomes are produced by buds located on for tuber viability. Rhizomes extend in the tubers and on basal bulbs, and grow 'either into soil profile and form either tubers in chains new aerial shoots with a basal bulb or expand or basal buds related to aerial shoots. plagiotropically and form new tubers. On CE, Tubers bear numerous buds, the sprouting tubers are terminal, whereas on CR they of which is regulated by apical dominance; dormant buds remain viable in soil for develop on rhizomes in chains,of up to fifteen prolonged periods. Damage to shoots, tubers tubers (5,22). or rhizomes triggers sprouting of dormant Basal bulbs and tubers function both as buds and renewed growth. Propagation is storage and reproductive organs. They differ mainly by their position; basal bulbs are . primarily by tubers, and rarely by seeds. directly connected to an aerial shoot. As rhizomes elongate they form tubers and ensure Introduction the translocation of nutrients and assimilates Cyperus rotundus L. (purple nutsedge) is between above ground and underground parts. considered to be the worst weed in the world, After planting a tuber under suitable because of its ubiquitous presence in warm conditions, a shoot emerges 47 days later, regions, its propagation potential and strong and 1530 days later a new tuber is formed. competitive capacity, and the difficulty to At that stage the plant is `established' as it is control, when established, by mechanical or capable of spreading or surviving even follow- chemical means. Purple nutsedge is believed ing the destruction of the aerial parts (4,5,9). to be a native of the tropics (14). This weed In young plants, shoot development is swift, has spread with the development of intensive, followed by a rapid increase in tuber formation irrigated agriculture in warm countries, and (5,9). through the increased international transport of The number of tubers produced by a CR plant material (2,5). It occurs at present in plant is considerable. In Israel, established more than 90 countries, on most continents, on plants formed more than 200 new tubers and agricultural and uncultivated land, under basal bulbs per m2 per week (8). In Georgia, tropical, subtropical and Mediterranean U.S.A., planted tubers produced 1000 bulbs climates, between latitudes 35° N and 35° S and 2300 tubers per m2 by 20 weeks after (6,14,21). planting, with a dry weight of 3 kg m-2 (5). In this paper I examine the mechanisms of Differences in the rate of tuber formation are establishment, propagation and dissemination related to climatic and edaphic conditions which combine to make this species such a (14). After forming a dense network, the tuber serious pest to cultivated crops. Where data population tends to stabilize or even slightly are available, the characteristics of purple decrease in subsequent seasons (19). nutsedge will be compared with Cyperus Proceedings of the First International Weed Control Congress, Melbourne 1992 9 5

Under similar conditions fewer, smaller (3,5,14,21). With decreasing tempëratúres:the tubers aré produced by CE than by CR, shoots wither. However, the vascular system of however, the seasonal tuber production of CE rhizomes remains intact after the aerial parts is also remarkable; a tuber reportedly produced have decayed and the tubers formed on them 1900 shoots and 7000 tubers in one year (20). overwinter (22). Tubers of both types of nutsedge maintain Factors affecting sprouting and their viability at the maximum temperatures development of tubers recorded in most warm regions; it is the Apical dominance and dormancy. minimum temperature which determines the Ten or more buds are located on a tuber, and seasonal development and the geographical their sprouting is regulated by apical domi- distribution of the species. Tubers of CR nance. On CR, apical tubers in the chain and exposed to 2 °C for 3 months lost their apical buds of the tuber sprout first, inhibiting germinability (18). In North America the development of more distant buds. Within an expansion of CR is limited by the isotherm of intact network, quiescent buds and chain 1.1 °C average minimum air temperature in tubers retain viability while remaining dor- January, corresponding to 0 °C at 10 cm soil mant for prolonged periods (14,16,19,22). depth (18). . Fifty to one hundred percent of CR tubers, Tubers of CE are more resistant to low collected all year round from plants of various temperatures than CR; their minimum sprout- ages, sprouted under adequate temperature and ing temperature is 12 °C and tubers may moisture conditions without marked seasonal tolerate 20 °C during winter (15,19). differences. Newly formed tubers also Moisture sprouted readily (10). Tubers of CE showed a CR grows in a wide range of soil moisture, clear seasonal dormancy, with those including flooded soil (17,21). Tubers sprout overwintering having a higher sprouting readily between 20% and 80 %, and most capacity than those produced in autumn rapidly at 40 60% field capacity. Tubers did (15,19,20). not sprout in water with a low oxygen level, Severing the tubers or the connecting but maintained their viability even when rhizomes, for example, by cultivation, breaks steeped in water for 200 days (4,11,14,21). the dormancy of the chain and induces sprout- Desiccating the tubers, in shade or in ing. Mechanical or chemical suppression of sunshine, reduces their sprouting capacity. As the top - growth is followed by prolific emer- the moisture content of tubers (normally 55 gence of new shoots (10,14,16). Inhibitory 70 %) decreases below 10 12 %, germinability compounds present in the foliage and the is lost (12). A system of CR control has been tubers are probably involved in dormancy (14). developed in areas with a hot and dry summer, A viable tuber can sprout several times based on deep tillage which cuts the tuber before its food reserves are exhausted. The chains from their moisture supply and causes longevity of tubers in soil is apparently related their. desiccation (1). to the low oxygen level in the soil profile, Light which induces dormancy, and therefore Tubers sprout normally in the dark and are increases with depth. Dormant tubers of CE also able to sprout in white and coloured light are reported to remain viable in soil for 35 (21). Both CR and CE possess the C. years (15). dicarboxylic acid photosynthetic pathway, Temperature which allows plants to assimilate CO2 effi- Minimum, optimum and maximum tempera- ciently at high temperatures and light tures for sprouting of CR tubers are approxi- intensities (19,22). , mately 20, 30 ' 35 and 45 °C respectively The shoot and tuber production of both (4,10,21). Under alternate temperatures, some nutsedges is correlated with the intensity of sprouting may already occur at a temperature photosynthetically active radiation, and is above 15 °C, causing early competition to crops sensitive to shading (19). Decreasing the planted in spring.. incident light intensity by shading with plastic Shoot and tuber formation are closely sheets, or with companion plants, causes related to temperature changes. Plant growth is etiolation of the shoots and reduces tuber slow below 20 °C, and most rapid at 26 35 °C formation (5,14). However, only a completely; 9 6 Proceedings of the First International Weed Control Congress, Melbourne 1992 opaque cover, laid on the soil for a prolonged a continuous infestation had been formed period, can eradicatea severe infestation of covering 7.6 m2, and up to 2.8 m from the loci. purple nutsedge. At the end of the second season, the infestation In CE, short photoperiods stimulate tuber was 56 m2 and extended up to 5.4 m from the formation and long photoperiods promote loci. Spread was slower during the cool shoot development (5,15,19). In CR the effect season, as all shoots wilted, and accelerated of photoperiod is less pronounced, particularly again in spring. in regions with limited fluctuations in The mean increase in area for the study daylength (10,14). period was 2.8 m2 per month, compared to 0.6 Depth m2 and 0.9 m2 per month for Sorghum In established plants of CR, the subterranean halepense and Cynodon dactylon grown under system, rhizomes and tubers, is generally similar conditions. The rapid expansion of CR concentrated in the upper 1520 cm of soil. reflects, the vigour of its underground system. Tubers have been recorded deeper, but rarely The two perennial grasses spread by rhizomes lower than 50 cm (10,19;22). Rhizomes which also function as storage and reproduc- penetrate and form tubers deeper in light tive organs. In nutsedge these functions are textured or frequently cultivated soils than in carried out separately by compact tubers and heavy soil (1,3,10,21). slender rhizomes. The depth at which tubers sprout in soil is The rapid expansion of CR has been limited by the available oxygen necessary for recorded elsewhere. For instance in Georgia, germination, and the amount of food reserves U.S.A., plants from tubers planted 90 cm apart in the tuber required to form a rhizome overlapped in five weeks; after 20 weeks sufficiently long enough to reach the soil approximately 5700 km of rhizomes had been surfacewhere it will produce a basal tuber produced per hectare (5). CE is also character- and emerge as a shoot. Under experimental ized by rapid spread; a single tuber produced a conditions, tubers of nutsedge sprouted and patch 2 m in diameter after one year (20). formed aerial shoots from a depth of 45 cm Dissemination by tubers (9,17,19) and occasionally even deeper (4). Tubers of both nutsedges are the primary Sprouting percentage and rapidity of emer- dispersal unit. They sprout under appropriate gence decrease with increasing depth, although conditions or remain dormant for extended at the end of a growing season the total periods, thus functioning like seeds of annuals number of tubers produced is similar for both (19). Tubers are spread from infested sites by, early- and late- emerging plants (9). for example, people, animals, farm equipment, Time and depth - regulation of tuber sprout- plant material, soil and water (2). ing have many important implications. As In urban areas transport of contaminated practically all undergound tubers are capable soil and propagation material to gardens is a of forming new plants, herbicidal treatments major cause of spread. Tubers of edible are only effective if the active compound is varieties of CE are sometimes imported translocated to all tubers. Also solarization, intentionally, and escape. In the Netherlands, which prodúces lethal temperatures of 50 tubers of CE have been introduced acciden- 60°C close to the soil surface, is insufficient to tally from warm countries with plant material; eradicate an established stand of nutsedge. On and are seriously infesting regions which the other hand, burying tubers deep in the soil, produce flower bulbs such as gladioli. by ploughing for instance, will not reduce the Propagation by seeds infestation. Plants of CR produce up to several thousand achenes (seeds) on each inflorescence (13,19), Expansion and dissemination but their viability is low (1,3,12) or nil Spatial expansion (6,10,14,19). In comparative studies, seeds of Spreading of CR from a single tuber was CE and other Cyperus species produced higher followed during two seasons in Israel (10). germination rates than CR (12). Three months after planting, shoots emerged Freshly harvested seeds of CR are dormant; up to 110 cm from the original tuber. The presumably because of their hard seed coat, expansion proceeded radially, at first follow- and a long period of after- ripening is required ing the path of the rhizomes. After six months before they germinate (1,17). The half -life of Proceedings of the First International Weed Control Congress, Melbourne 1992 9 7

CE seeds. buried 5 cm in soil was found to be tubers. Weed Research 12, 3481032 ,; about 500 days (13). Seedlings of CR have 10. Horowitz, M. (1972). Effects offrèquent rarely been observed. In California, seedlings clipping on three perennial weeds, Cynodon of CE grown in a glasshouse appeared less dactylon (L.)Pers., Sorghum halepense (L.) vigorous than sprouts of tubers, and'no seed- Pers. and Cyperus rotundas. Experimental lings have been found in the field (7). In Agriculture 8, 225 -34. Zimbabwe, 0.8% and 0.03% of CE seeds 11. Horowitz, M. (1972). Effects of desiccation produced seedlings under irrigated and rain - and submergence on the viability of rhizome fed conditions, showing that adequate soil fragments of bermudagrass and johnsongrass moisture is critical for establishment (13). and tubers of nutsedge. Israel Journal of Genetic analysis of populations of both Agricultural Research 22, 215 -20. nutsedge species found in California exhibited 12. Justice, O.L. and Whitehead, M.D. (1946). limited genetic variability, indicating primarily Seed production, viability and dormancy in the asexual reproduction, even for CE (7). Most nutgrasses Cyperus rotundas and authors (6,14,15) conclude that for each of C. esculentus. Journal of Agricultural Re- these species, propagation by seed is not the search 73, 303 -17. most important means of spread, even though 13. Lapham, J. and Drennan, D.S.H. (1990). The viable seeds constitute á source of infestation fate of yellow nutsedge (Cyperus esculentus) (1,12,13). seed and seedlings in soil. Weed Science 38, 125 -8. References 14. Mercado, B.L. (1979). A monograph on Cyperus rotundas L. Biotrop Bulletin 15, 1-63. 1.Andrews, F.W. (1940): A study of nutgrass ( Cyperus rotundas L.) in the cotton soil of 15: Mulligan, G.H. and Junkins, BE. (1976). The Gezira. 1. The maintenance of life in the tuber. biology of Canadian weeds. 17. Cyperus Annals of Botany 4, 177 -93. esculentus L. Canadian Journal of Plant 2.Bendixen, L.N. and Nandihalli, U.B. (1987). Science 56, 339 -50. Worldwide distribution of purple and yellow 16. Muzik, T.J. and Cruzado, HJ. (1953). The nutsedge ( Cyperus rotundas and C. effect of 2,4 -Don sprout formation in Cyperus esculentus). Weed Technology 1, 61 -5. rotundas. American Journal of Botany 40, 3.Bhardwaj, R.B.L. and Verma, R.D. (1968). 507 -12. Seasonal development of nutgrass (Cyperus 17. Ranade, S.B. and Bums, W. (1925). The rotundus L.) under Delhi conditions. Indian eradication of Cyperus rotundas L. Memoirs of Journal of Agricultural Science 38, 950-7.. Indian Department of Agriculture, Botany 4. Guehne, K.M. (1974). Knollenaustrieb, Series 13, 98 -192. Entwicklung und Bekämpfung von Cyperus 18. Stoller, E.W. (1973). Effect of minimum soil rotundus L. in Abhängigkeit von einigen temperature on differential distibution of ökologischen Faktoren. Ph.D Thesis, Cyperus rotundas and C. esculentus in the Abteilung Herbologie, Universität Hohenheim, United States. Weed Research 13, 209 -17. Germany. 19. Stoller, E.W. and Sweet, R.D. (1987). Biology 5.Hauser, E.W. (1962). Development of purple and life cycle of purple and yellow nutsedge. nutsedge under field conditions. Weeds 10, ( Cyperus rotundas and C. esculentus). Weed 315 -21. Technology 1,66 -73. 6. Holm, L.G., Plucknett, D., Pancho, J.V. and 20. Tumbelson, M. and Kommedahl, R. (1962). Herberger, J. (1977). The World's worst Factors affecting dormancy in tubers of weeds. distribution and biology. The Univer- Cyperus esculentus. Botanical Gazette 123, sity of Hawaii Press, Honolulu, Hawaii. 186 -90. 7.Holt, J.S. (1987). Yellow and purple nutsedge: 21. Ueki, K. (1969). Studies on the control of California distribution, biotypes and seed nutsedge (Cyperus rotundas). On the germina- production. Proceedings 39th Annual Califor- tion of a tuber. Proceedings 2nd Asian- Pacific nian Weeds Conference, pp. 87 -9. Weed Control Interchange, Philippines, pp. . 8.Horowitz, M. (1965). Data on the biology and 355 -69. chemical control of the nutsedge ( Cyperus 22. Wills, G.D. (1987). Description of purple and rotundas) in Israel. PANS (C) 11, 389 -416. yellow nutsedge (Cyperus rotundas and 9.Horowitz, M., (1972). Growth, tuber formation C. esculentus). Weed Technology 1, 2 -9. and spread of Cyperus rótundus L. from single