Distribution, biology and management of Mimosa ... - Weeds Australia

Distribution, biology andmanagement of Mimosa pigrain Sri LankaB. Marambe, 1 L. Amarasinghe, 2 K. Silva, 3 G. Gamage, 1 S. Dissanayake 1and A. Seneviratne 1AbstractMimosa, Mimosa pigra L., was first reported in Sri Lanka in 1997. The species is mainlyconfined to the central and north-western provinces of Sri Lanka. The plant has colonisedalong the river banks of the Mahaweli River, which is the main supplier of irrigation waterto the agriculture-dominant dry zone of the country. Use of river sand for constructionwork was identified as a major method of seed dispersal, apart from seeds being transportedwith river water flow. GPS technology is currently being used for monitoring theextent of spread of this species.Mimosa seeds were 100% viable after four years of storage at room temperature (28±2°C)and also at 8°C. The onset of flowers was first observed at 12–14 weeks after planting. Theinitial growth of the weed was slow, but the height increased at a rate of 2.4–2.6 cm day –1during the first 8–12 weeks. From 12 weeks, the stem dry weight of mimosa increased at amore rapid rate than the root dry weight. The relative growth rate (RGR) increased untilonset of flowers and then decreased. The soil seed-bank density within the canopy diameterof the naturally grown mimosa plants varied from 2,336 to 46,410 seeds m –2 . Glyphosateat the dosage of 1.44 kg active ingredient ha –1 effectively controlled mimosa seedlingsless than six months old, when applied three times repeatedly at four-month intervals onthe same set of seedlings. Mimosa seeds did not germinate in the presence of one-monthold Panicum maximum Jacq. at a population density of 16 plants m –2 . Awareness programsconducted for the communities in the infested areas have resulted in several communityparticipatory activities to eradicate small patches of mimosa from the Central Province.Keywords: mimosa, Sri Lanka, herbicide control, growth rates, spread.IntroductionIntentional and unintentional introductionscontinue at a rapid pace today, accelerated by therecent rise in international trade. Introduction and1 Department of Crop Science, Faculty of Agriculture,University of Peradeniya, Sri Lanka.2 Plant Protection Service, Department of Agriculture,Ministry of Agriculture and Livestock, Sri Lanka3 Biodiversity Secretariat, Ministry of Environment andNatural Resources, Sri Lanka.spread of the majority of invasives are linked eitherdirectly or indirectly to human activity with aneconomic or aesthetic objective. People areinvolved in intentional transportation and introductionof some non-native species, for food, fibre,medicine, ornament or scientific curiosity. Seeds ofother plants have been introduced accidentally/unintentionally in sacks of seed grain, wool orcotton, in mud stuck to machinery or in ship ballast.Human activities such as farming, irrigation,forestry and mining have made it easier for thesenon-native species to become established by85

Research and Management of Mimosa pigraremoving native vegetation, disturbing the soil andaltering the availability of water and nutrients.The importance of understanding the impact ofalien invasive plants in Sri Lanka, a small island inthe Indian Ocean, has been felt recently. Severalalien plants found in Sri Lanka have been reportedas spreading at an alarming rate, threatening thenatural and agricultural ecosystems of the country(Marambe et al. 2000). Sri Lanka has considerableexperience where deliberate introduction of alienplants has finally resulted in them becoming invasiveor weedy (Wijesundera 1999). It is importantto note that plants that are now invasive or weedy,once appeared to be non-invasive when theirpopulations were small, or when they were onlyfound in habitats influenced by people.Mimosa, Mimosa pigra L, also known as giantsensitive plant, catclaw mimosa and giant mimosa(English), and katugas (Sinhala), is an introducedplant to Sri Lanka. The species is a perennial shrubor small tree that reproduces only by seeds(Creager 1992), and may grow to a height of about4–6 m. A native of Mexico, southern Venezuela orthe central Amazon basin, it has become a seriousagricultural, environmental and economicproblem in many countries where it has beendeliberately or accidentally introduced. In itsnative range, this plant rarely causes problemsand grows as scattered plants, seldom more than2 m high, or as a small thicket (Creager 1992).However, in many introduced environments, theplant has behaved aggressively, forming densethickets covering large extents of land and threateningthe natural biodiversity.This alien invasive plant was first identified inSri Lanka from the banks of Mahaweli River in theCentral Province (Amarasinghe and Marambe1997). In early 1996, the plant was found to occupya 1 km stretch of riverbank and adjoining lowlyingareas that get periodically inundated.However, the results of a recent survey (Marambeet al. 2000) indicated that the weed has denselycovered a 20–25 km strip along the banks of theMahaweli River, and also spread into about 46locations in 4 districts across 3 provinces in 4 agroecologicalzones. Apart from the banks of theMahaweli River, mimosa was also found in abandonedpaddy fields, other river and stream banks,home gardens, roadsides, waterways and newconstruction sites. This alien invasive weed, whichis said to have colonised Sri Lanka from the early1980s, has become a serious environmental threatto agricultural lands, abandoned lands andnatural reserves in Sri Lanka, reducing landproductivity and value (Marambe et al. 2000,Marambe 2001, Marambe et al. 2001a). This paperreports the results of studies conducted in SriLanka to understand the biology and distributionof mimosa in Sri Lanka and potential controlmeasures for the invasive alien species.Biology of mimosaSeed storage and germination ofmimosaExperiments carried out in Sri Lanka indicatedthat seed germination of mimosa was enhancedsignificantly after sand scarification whencompared to untreated seeds (Figure 1). Thiscould be due to the removal of the hard seed coatof mimosa via sand-scarification, as reported byCreager (1992). This was also evident by the poorresponse of mimosa seeds to continuous soakingM. pigraSeed Percentage Germination germination % of100806040200un-treated Untreated seeds Sand-scarified sand seeds soaked Soaked seeds0 1 2 3 4Number of years of storageNumber of years of storageFigure 1.Germination percentage of mimosa seeds after different periods ofstorage. The data presented are the average of the results ofstorage under room temperature (28±2°C) and at 8°C, in six replicates.The vertical bars represent the standard error of the means.86

Distribution, biology and management in Sri Lankain water, which could be due to the impermeableseed coat preventing water entry (Brecke andDuke 1980). Dillon and Forcella (1985) alsoreported that the germination of unscarified seedsof mimosa is significantly lower (0–23%). Lonsdale(1993) reported that, under natural conditions,the hard seed coat of mimosa may getdamaged due to many reasons such as microbialactivities, temperature fluctuations, soil erosion,damage by animals, equipment and watercurrent, and thus enhance germination. Theresults of the studies carried out in Sri Lankaclearly indicated the ability of mimosa seeds toremain viable for several years and germinaterapidly following sand scarification.In the Central Province of Sri Lanka, mimosaflowers throughout the year. The studies on podand seed characteristics of mimosa found in thisprovince revealed that the maximum pod size is13.4 cm containing 8–20 seeds per pod, seed size4.2 ± 0.2 (length) mm ¥ 2.2 ± 0.1 (width) mm, andseed weight 8.9 ± 0.4 mg per 100 seeds.About 99% of the seeds germinated after fouryears of storage at 8°C and room temperature(28±2°C), but only after sand scarification (Figure1). Marambe et al. (2001b) also reported that 99%of seeds germinated after one year of storageunder the same conditions. Lonsdale (1993)reported that seeds of mimosa could be viable forat least 23 years in sandy soil. However, underfield conditions the longevity of seeds could vary(Lonsdale et al. 1988).Seedling growth of mimosaThe first flowering occurred 12 weeks afterplanting, at which time the average plant heightwas 77 cm. However, trees did not produce morethan two flowers per plant at the beginning andnone of them produced seeds after first flowering.The pods were obtained only from flowers thatwere produced at 18 weeks, but still the averagenumber of flowers per plant did not exceed four.The results are contrary to those of Lonsdale andAbrecht (1989), who reported that, under idealconditions, mimosa begins to flower within 6–8months of emergence. The difference could be dueto the climatic variations of the present studycompared with those reported by Lonsdale andAbrecht (1989).Plant height increased slowly during the initialgrowth stages, but rapidly (2.4 cm day –1 ) from8–12 weeks (Marambe et al. 2001b). Lonsdale(1992) reported a slower but significant increase inplant height at a rate of 1.1 cm day –1 during thefirst 90 days after germination in Thailand. Theresults indicate the importance of studying thegrowth and development of mimosa underdifferent environmental conditions before recommendationof any control measure. The rootlength increased rapidly up to 12 weeks but at alesser rate until 18 weeks. The higher root growthat the initial growth phase of mimosa is necessaryto provide anchorage for the plant and enable theplant to absorb water and nutrients for growth(Egley and Duke 1985). The number of leaves perplant gradually increased up to 14 weeks and fellthereafter.The absolute growth rate (AGR) of mimosaduring the first 18 weeks of growth indicates thatthe rate of dry matter increase took place at asimilar rate. The relative growth rate (RGR),which indicates the efficiency of dry matterproduction, fell with time. The highest reportedRGR was 0.44 at 12 weeks (Marambe et al. 2001b).Patterson and Flint (1983) reported that the RGRof a plant could fall even under favourable growthconditions mainly due to the development of nonphotosynthetictissues (roots and stems) asobserved in the present study.From the results of the experiments carried outin Sri Lanka it can also be deduced that themajority of photosyn-thates produced in the plantduring 14–18 weeks were accumulated in theshoot (stems) rather than being translocated to theroots. However, Brecke and Tobola (1996)reported that soil nutrient levels have an effect ondry matter accumulation and translocation todifferent plant parts. Thus, experiments should becontinued under different soil conditions to elaboratedry matter partitioning in mimosa.Distribution of mimosaField surveys were started in 1999 to identify thedistribution of mimosa in the Central Province ofSri Lanka. In addition to flowing water, the use ofriver sand for construction purposes has beenidentified as the major pathway of mimosa seedspread to different areas in Sri Lanka especiallythe uplands (Marambe et al. 2000). Mapping thedistribution of mimosa using GPS technology isstill in progress, under the financial assistance ofthe National Research Council (NRC) of Sri Lanka.Preliminary survey data have clearly indicatedthat mimosa has colonised many water bodies andoccurs along rivers/canals that flow through theCentral Province of Sri Lanka (Marambe et al.2000).Control of mimosaChemical controlPot experiments carried out in Sri Lanka usingmimosa seedlings of different ages indicated thatrepeated use of glyphosate, a non-selective87

Research and Management of Mimosa pigrasystemic herbicide, at the rate of 1.44 kg of activeingredient ha –1 (applied three times at four-monthintervals) successfully controlled seedlings lessthan six months old (Figure 2). Aerial applicationof several herbicides, including glyphosate, hasbeen reported to be successful for controllingdense stands of the weed in Australia (Miller andSiriworakul 1992, Pitt and Benyasut 1992), whileground spraying has been recommended forsmall infestations. However, in the Sri Lankanscenario, field experimentation to control fieldstands of the weed with the use of herbicides wasnot conducted, due to the threat of chemicals tothe aquatic ecosystems where this invasive alienplant has colonised.BurningPreliminary studies conducted have indicatedthat young and mature mimosa plants are difficultto control by burning, unless they are firstuprooted and dried. In several situations, whereburning was evaluated for mimosa control underupland conditions, profuse regenerativebranching of plants and increased seed germinationof the soil seed-bank was observed two tothree months after burning (B. Marambe, unpublisheddata). Miller (1988) reported that fire canincrease the germination of the soil seed-bank bybreaking seed dormancy. However, due to hightemperatures, fire may also kill a proportion ofseeds found on the soil surface.Agronomic methodsSuccessful results were obtained in field andpot experiments to control mimosa populations atyounger stages with the use of Panicum maximumat a plant population density of 16 plants m –2 .Mimosa seeds did not germinate in the presenceof one-month old P. maximum seedlings (Figure 3).Miller (1988) reported that mimosa seedlings areless competitive in the presence of dense stands ofgrasses/pastures. In Sri Lanka, P. maximum is anintroduced pasture grass, which has beenreported to escape human management andbecome an invasive species under differentecosystems (Marambe et al. 2001a). Hence, precautionsshould be taken in restoration of ecosystemsinfested with mimosa to ensure that another invasivedoes not colonise the available space. To overcomethese problems, Miller and Lonsdale (1992)reported that in Australia native grasses such asHymenachne acutigluma (Steudal) Gilliland, andOryza australiensis Domin are potential competitorsagainst mimosa.Public awarenessSeveral attempts have been made to createawareness among all stakeholders to prevent thespread and control the existing populations ofmimosa in Sri Lanka. The Biodiversity Secretariatof the Ministry of Environment and NaturalResources of Sri Lanka, together with severalgovernmental and non-governmental organizationsand the University of Peradeniya, hasconducted workshops and seminars aimed atdifferent target groups, on the detrimentalimpacts of this invasive alien plant to the ecosystemsof the country. At the provincial level,several local governments in the Central Provincehave produced leaflets/pamphlets to be distributedamong the general public, as part of theawareness campaign of the detrimental impacts ofmimosa. As a result of these awarenesscampaigns, community participation has helpedto eradicate small patches of mimosa from theCentral Province of Sri Lanka.Reduction in dry weight (%)120100806040202 months old4 months old6 months old8 months old12 months old00 0.36 0.72 1.08 1.44 1.80 2.16Figure 2.Dosage of glyphosate (kg a.i. per ha)Control of mimosa seedlings of different ages using glyphosate.The herbicide was applied three times at 4-month intervals, on thesame set of seedlings at different ages. The vertical bars representthe standard error of the means.88

Distribution, biology and management in Sri LankaPercentage germination100806040202 weeks4 weeks8 weeksFigure 3.00 8 16 24 32 40 48 56 64Two national workshops organised by theMinistry of Forestry and Environment in 1999 incollaboration with the Sri Lanka Association for theAdvancement of Sciences (SLAAS), and in 2000 incollaboration with the National AgriculturalSociety of Sri Lanka (NASSL), highlighted theimportance of a coordinated mechanism to controlthe invasive alien weed species in the country(Marambe 1999, Marambe 2000). Currently, aNational Strategy is being developed by theMinistry of Environment and Natural Resourceswith the objective of making the prevention ofspread of, and the control and restoration of ecosystemsinfested with invasive alien species includingmimosa an issue of national importance. This isexpected to strengthen the existing programs byproviding a coordinated mechanism and permittingexploration of the potentials of biologicalcontrol of the weed in collaboration with internationalorganisations, to overcome the negativeimpacts of mimosa in Sri Lanka.AcknowledgementsThe authors thank the National Research Council(NRC) of Sri Lanka for providing financial assistanceto carry out part of the studies indicated inthis paper (Grant No. NRC/00-20). B. Marambethanks the Australian International SeminarSupport Scheme (ISSS) for sponsoring attendanceat the symposium.ReferencesAmarasinghe, L. and Marambe, B. 1997. Mimosa pigra L.: anew weed in aquatic habitats of Sri Lanka. Sri LankanJournal of Agricultural Sciences, 34, 81–98.Brecke, B.J. and Duke, W.B. 1980. Dormancy, germinationand emergence characteristics of fall panicum(Panicum dichotomiflorum) seed. Weed Science, 28,683–685.Density of P. maximum (plants/m 2 )Seed germination percentage of mimosa under differentdensities of one-month-old Panicum maximum. The verticalbars represent the standard error of the means.Brecke, B.J. and Tobola, P. 1996. Growth and developmentof wild poinsettia (Euphorbia heterophylla) selections inpeanut (Arachis hypogaea). Weed Science, 45, 575–578.Creager, R.A. 1992. Seed germination, physical and chemicalcontrol of catclaw mimosa (Mimosa pigra var.pigra). Weed Technology, 6, 884–891.Dillon, S.P. and Forcella, F. 1985. Fluctuating temperaturebreak seed dormancy of catclaw mimosa (Mimosapigra). Weed Science, 33, 196–198.Egley, G.H. and Duke, S.O. 1985. Weed seed germination.In: Duke, S.O., ed., Weed Physiology Vol. 1. Reproductionand Ecophysiology. CRC Press, NY, pp. 27–64.Lonsdale, W.M. 1992. The biology of Mimosa pigra L. In:Harley, K.L.S., ed., A guide to the Management ofMimosa pigra. Commonwealth Scientific and IndustrialResearch Organisation, Canberra, pp. 8-32.Lonsdale, W.M. 1993. Losses from the seed bank ofMimosa pigra: soil micro-organism vs temperature fluctuations.Journal of Applied Ecology, 30, 654–660.Lonsdale, W.M. and Abrecht, D.G. 1989. Seed mortality inMimosa pigra, an invasive tropical shrub. Journal ofEcology, 77, 371–385.Lonsdale, W.M., Harley, K.L.S. and Gillett, J.D. 1988. Seedbank dynamics of Mimosa pigra, an invasive tropicalshrub. Journal of Applied Ecology, 25, 963–976.Marambe, B., ed. 1999. Proceedings of the First NationalWorkshop on Alien Invasive Species in Sri Lanka. Ministryof Forestry and Environment of Sri Lanka, 73 pp.Marambe, B., ed. 2000. Proceedings of the Symposium onAlien Invasive Species in Sri Lanka: Their Impact on Ecosystemsand Management. Joint Publication of the Ministryof Forestry and Environment of Sri Lanka and theNational Agricultural Society of Sri Lanka, 63 pp.Marambe, B. 2001. Alien invasive plants threatening theagro-ecosystems of Sri Lanka. In: Assessment andManagement of Alien Species that Threaten Ecosystems,Habitats and Species. Secretariat of the Convention onBiological Diversity, Montreal, CBD Technical SeriesNo. 1, pp. 85–86.Marambe B., Amarasinghe, L. and Dissanayake S. 2001b.Growth and development of Mimosa pigra: an alieninvasive plant in Sri Lanka. In: Brundu, G., Brock, J.,Camarda, I., Child, L. and Wade, M. eds, Plant Invasions5. Backhuys Publishers, Leiden, The Netherlands,pp. 115–122.89

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