conyzoides: an Alien 5Invasive Weed in Shalinder Kaurl, Daizy R. Batish2, R. K. Kohli2 and H.P. Singhl

1Department of Environment Studies, Panjab University, Chandigarh, India; 2Department of Botany, Panjab University, Chandigarh, India

Introduction and hybridization (Mooney and Cleland, 2001). Furthermore, invasive reduce Worldwide, invasion by exotic alien plantsbiodiversity viadegradationof wildlife has caused a significant change in structure habitat, thus adversely affecting product- and composition of vegetation leading toivity,ecosystem properties and eco- homogenization of flora (Cushman andsystem development at the global level Gaffney, 2010). Due to increased global- (Masters and She ley, 2001; Kolbet al.2002; ization and burgeoning human population,Davies and Svejcar, 2008). there has been an unprecedented increase India is one of the richest centres of inmovement(bothintentionalandbiodiversity due to its wide range of climatic unintentional)ofspecies beyond theirconditions and geography (UNEP/WCMC, natural biogeographical range into new2000). It hosts three biodiversity world hot environments. In fact, the spread of invasivespots, namely the Western Ghats, the species is occurring at an exceptionally highEastern Himalayas and the Indo-Burma rate throughout the world and is amongstregion, regions showing high levels of oneofthemajorthreatstoglobalendemism and species diversity. However, biodiversity. It has greatly enhanced theduring the last few decades, these are under interestofscientistsinstudyingtheenormous threat due to various anthro- magnitude of occurrence and impact ofpogenicpressuressuch astourism, invasive species(Davis,2009).Invasive industrializationandurbanization,in plants damage ecosystems both economicallyaddition to the widespread introduction of and ecologically and, out of these, ecological invasiveexoticspecies by humans. A impacts are more difficult to assess thannumber of exotic specieseither economic effects (Pimentelet al.,2005).introduced deliberately or having entered Invasive plants affect native plants directly accidentallyhave negativelyaffected by competition for soil resources, light andecosystem functions, reducing the effective space, as well as indirectly through alteration habitat of endemic species and, in turn, ofecosystemprocesses,servicesandhave made the restoration of native species ecological functioning such as soil nutrient difficult. cycling and pollination, etc. (Goodell, 2008; In India there are a number of invasive Weidenhamer and Callaway, 2010). Invasive weeds which have caused havoc with native species reduce the number of native species biodiversity (Koh liet al.,2009). It is very and may even lead to their extinction owingimportant to know and understand their to competitive exclusion, niche displacementbiology,ecology and factorsimparting

© CAB International 2012. Invasive Alien Plants: An Ecological Appraisal for the Indian Subcontinent (eds J.R. Bhatt et al.) 57 58 S. Kau r et al.

invasiveness in order to manage them. ThisWest Africa, Australia, Colombia, Costa chapter provides details regarding Ageratum Rica, Ecuador, Fiji, French Polynesia, the conyzoides, an invasive alien weed in India. Guam Islands, the USA (Hawaiian Islands), Tonga, Vanuatu, Palau, Mauritius, Nicar- agua, the Solomon Islands, Papua New Guinea, Samoa and South-east Asia (includ- ing China, India, the Philippines, Singapore, Ageratum conyzoides (family ) isThailand, Vietnam, Cambodia, Malaysia and one such rapidly colonizing invasive alienIndonesia), Brazil and Korea (Kong et al., species that has become a troublesome weed2004; Kohli et al., 2006; Sankaran, 2007; over a wide range of ecosystems in tropical Batish et al., 2009a). and subtropical countries (Batish, 2008; In Hawaii, A. conyzoides grows up to 1300 Batish et al., 2009a, b). It is one of about 30m above sea level (Wagner et al., 1999). In species of the genus Ageratum, all of which Pacific islands the weed has been found originated in America (Okunade, 2002). Thegrowing in different habitats such as crops, genusAgeratumiswidelydistributedpastures,plantations,wastelandsand throughout America, although most taxaroadsides (Swarbrick, 1997; PIER 2008). In have been reported in Mexico, Central Fiji, A. conyzoides is cultivated but it has now America, the Caribbean and Florida (Ming,become invasive and naturalized in grass- 1999). The literal meaning of Ageratum islands, forests, forest clearings and along non-ageing (referring to the longevity of itsroadsides and trails up to an elevation of 950 or of the whole plant), with itsm (Smith and Albert, 1991; Sankaran, 2007). origins in the Greek word ageras, whereasIt has been reported to be a weed of plant- the species name conyzoides is derived fromations and waste areas in Tonga (Yuncker, konyz, the Greek name for Inula helenium L., 1959) and Guam (Stone, 1970). In New which it resembles (Kissmann and Groth, Guinea, A. conyzoides is spread up to 2000 m 1993). The English names of the plant, goatabove sea level in both waste and cultivated weed or billy goat weed, derive from itslands, in plantations, pastures and along peculiar odour likethat of male goatroadsides (Henty and Pritchard, 1975). (Okunade, 2002). Johnson (1971) divided In the Galapagos Islands the plant can be the taxon A. conyzoides into two subspecies,seen in moist uplands (McMullen, 1999). i.e.latifoliumand conyzoides,of whichThe species has been reported to be one of latifolium is found throughout the Americasthe most dominant weeds of upland crops whereas conyzoides has a pantropical distri-throughout South-east Asia (Kato-Noguchi, bution. 2001). In Central Sulawesi (Indonesia), A. The plant is now found as a weed of overconyzoides was recorded as an invasive weed 36 crops(including plantations)in 46in coffee and cacao plantations and in the different countries (Holm et al., 1977). Itsubmontane rain forests of Lore Lindu has been ranked as 19th of the world's worst National Park (Siebert, 2002; Ramadhanil et weeds (Holm etal.,1977). Waterhouseal., 2008). (1993) ranked A. conyzoides as the 15th most InSouthAfrica,A.conyzoides was troublesome weed of South-east Asia andintroduced in 1949 as an ornamental plant the Oceanic Pacific. and has now become invasive in many parts, including reserves and protected areas like Kruger National Park (Foxcroft et al., 2008). Global distribution ofAgeratum It grows as an exotic herb in the riparian conyzoides zones of South African rivers (Hood and Naiman, 2000). Nel et al. (2004) conducted a Ageratum conyzoides, a native of Centralsurvey of riparian zones in South Africa and America and the Caribbean, is now foundconcluded that A. conyzoides is one of the throughout the world (Xuan et al., 2004).most widespread and abundant invasive The alien range of A. conyzoides includes riparian weeds. Ageratum conyzoides 59

In China, the species was first recorded in In Lord Howe Island (Australia), A. conyzoides The Flora of Hong Kong by Bentham in 1861, originated as a cultivated plant but has now and later in late 19th century in southernbecome a common weed (GISD, 2010). In Yunnan Province (Yan et al., 2001). It wasZimbabwe, the weed is invasive in nature introduced as an ornamental plant, and hasand is commonly found in abandoned and now invaded the ruderal habitats anddisturbed sites, open woodlands and along croplands of central China, South China,stream and seepage zones at an altitude Xizang and the lowlands, mountains, plainsrange of 700-1660 m (Hyde and Wursten, and hills of Yangtze Drainage (Yan et al., 2010). Akter and Zuberi (2009) reported A. 2001; Huang et al., 2009). conyzoides as an invasive weed in different In Australia, A. conyzoides has beenhabitats such as fallow lands, homesteads, reported to be a major invasive weed ofroadsides and railway tracks in . crops,pastures and disturbedsitesin Additionally, the weed is also found/ northern Queensland and the Northernlisted as invasive in several other countries Territory (Holm et al., 1977; Jessup, 2002). (Table 5.1).

Table 5.1. Global distribution of Ageratum conyzoides. Region Reference(s) Continental Australia, Pacific offshore islands, Indian Holm et a/. (1977); Orchard and Anthony Ocean offshore islands, Christmas Island Group, (1994); Swarbrick (1997); Wagner et a/. Norfolk Island (Australia) (1999) Commonwealth of the Northern Mariana Islands, Fosberg et a/. (1975); Wagner et a/. (1999); Lehua Island, Molokai Island, Maui Island, Hawaiian PIER (2008); USDA-ARS (2009) Islands, Guam Island, Virgin Island (America) Chuuk Islands, Kosrae Island (Federal States of Manner and Mallon (1989); Josekutty et a/. Micronesia) (2002) Society Islands, Polynesia, Marquesas Islands (FrenchSachet (1983); Welsh (1998); Lorence and Polynesia) Wagner (2008) Offshore islands, Bonin (Ogasawara) Islands (Japan) Toyoda and Takeshi (2003); PIER (2008) Nauru Island (Nauru) Thaman et a/. (1994) New Caledonia Islands, Iles Loyaute (Loyalty Islands) Gargominy et a/. (1996) (New Caledonia) Niue Island (Niue) Yuncker (1943); Whistler (1988); Space et a/. (2004) Rock Islands, Angaur Island, Koror Island, Babeldaob Space et a/. (2003, 2009) Island, Malakal Island, Ngerkebesang Island (Palau) Philippine Islands (Philippines) Waterhouse (1993) Savai'i Island, Upolu Island, Western Samoa Islands Space and Flynn (2002); PIER (2008) (Samoa) Tonga Islands, Tongatapu Island (Tonga) Yuncker (1959) Wallis and Futuna Islands (Wallis and Futuna) Meyer (2007) Kingdom of Cambodia (Cambodia) Waterhouse (1993) People's Republic of China (China) Li-ying et a/. (1997) Republic of Indonesia (Indonesia) Waterhouse (1993) Republic of Singapore (Singapore) Waterhouse (1993) Taiwan Island (Taiwan) Li-ying et a/. (1997) Kingdom of (Thailand) Waterhouse (1993) Socialist Republic of Vietnam (Vietnam) Waterhouse (1993) La Reunion Island (France) MacDonald et a/. (1991) Maldive Islands (Maldives) Fosberg (1957) Mauritius and Rodrigues Islands (Mauritius) Holm et a/. (1977)

Source: GISD (2010). 60 S.Kau r et al.

Distribution in India be a major invasive weed on both the slopes and wetlands of Mothronwala swamp in the In India, A. conyzoides has been reported asDoon Valley, Uttaranchal (Gupta et al., existing prior to 1882 in The Flora of British 2006). Recently, A. conyzoides was found to India (Hooker,1882).Itwas probablybe one of the most predominant weeds in introduced as an ornamental plant in theMandhala watershed in Himachal Pradesh 1860s (National Focal Point for APFISN,(Rana et al., 2010). India, 2005), later attained a weedy habit The plant has also been found as a major and turned harmful to mankind. Its invasionweed in the littoral and swamp forests of and spread has caused ecological havoc to Assam (DOEF, 2010). In Arunachal Pradesh, indigenous floristic composition in variousA. conyzoides is one of the major weeds regions of India, including the north-westin West Siang (Singh et al., 2002) and the Himalayas, eastern Himalayas, central Indiamost dominant weed under canopy of and Western Ghats (Yoganarnarasimham,Dendrocalamus hamiltonii in tropical forests 2000; Silori and Mishra, 2001; Kohli et al.,(Arunachalam and Arunachalam, 2002). In 2006; Reddy et al., 2008). addition, the weed has also been reported in The weed has been reported as one of thenorth-eastern and southern India (Rao, major invasivespecies,growing to an2000) and the forests of the Gandhamardan elevation of 2400 m in Himachal PradeshHills range, Orissa (Reddy and Pattanaik, (Kohli et al., 2004; Dogra, 2008); in fact,2009). around 50% of the area in Himachal Pradesh state is said to be infested by this obnoxious weed (Batta, 1988). It has been reported to Spread of A. conyzoides in different be one amongst the ten most dominant habitats herbs in forest grassland edge, weed-infested areas and low-lying wet grassland of the JimAgeratum conyzoides is a serious problem of Corbett tiger reserve, Terai and Bhabarcultivated lands in the hilly tracts of north- regions (Rawat et al., 1997) and in thewestern India (Bansal, 1988), where it forms wetlandsofSamaspurBirdSanctuarydense thickets in commonly grown crops (Reddy et al., 2009) in Uttar Pradesh, India.such as chickpea, rice, maize and wheat, and Sitetal.(2007) surveyed the easternadversely affects crop yields (Kohli et al., Himalayan region of West Bengal (India)2006). Due to its enormous seed-producing and reported A. conyzoides as one of the capacity, fields left fallow are rapidly invaded most widely distributed weeds in variousand colonized by the weed. In Himachal crop lands and palm gardens. Pradesh the weed starts appearing at the Negi and Hajra (2007) studied flora of thetassel stage in maize, produces flowers and Doon Valley,north-west Himalaya andsets seeds by the time crop is harvested reported A. conyzoides as one of the invasive(Kanwar and Kharwara, 1988). exotics. The species has been reported to A study conducted by Reddi et al. (1977) occur in Veerapuli and Kalamalai forestdemonstrated that A. conyzoides is a major reserve (Swamy et al., 2000), tropical wetweed in ratoon sugarcane crop fields with a evergreen forests and the Anamalai Hillspopulation of 250-400 plants/m2. In maize (Muthuramkumar etal.,2006)of thefields, its population has been observed to Western Ghats of Tamil Nadu. A. conyzoides be 1000 plants/m2, thereby completely has been found to be a weed of disturbedcovering the ground surface (Anonymous, sites in the tropical forest of Little Andaman 1986-1987). Kanwar and Kharwara (1988) Island in the Bay of Bengal (Rasingamstudied the population of A. conyzoides in and Parthasarathy, 2009). It has been foundvarious fields and wastelands in Himachal to be one of the dominant species inPradesh(India).The populationof A. Agrakhal-Hindolakhal, Garhwal Himalaya,conyzoides was greatest in kitchen gardens Uttaranchal (Bughani and Rajwar, 2005). In(50 plants/m2) followed by maize fields addition, A. conyzoides has been reported to(20 plants/m2) and was least in meadows Ageratum conyzoides 61

(5 plants/m2). Ageratum conyzoides was also Habitat and characteristic features found to be a common weed of habitats such as grasslands, forest/plantation areas, waterPhysiognomically, A. conyzoides is an annual channels and wastelands in Chandigarherect aromatic herb that shows considerable (Arora, 1999), with maximum plant density variation in shoot height (59-120 cm) in a and dominance in forests (Table 5.2). stand at maturity stage (Table 5.3); however, In the hilly tracts of north-western India,the average height of plant is -1 m (Kumar particularlyinthelower and middleand Singh,1988). The sterniserect, Himalayas, weed infestation is increasing atbranched, cylindrical and decumbent, and an alarmingrateandithasseverely covered with fine, white hairs. Leaves are hampered the growth of native plants. opposite,ovateandtriangular,and Dogra (2008)carried out an extensivepubescent with the long petiole (1.5-2.0 cm survey of areas ranging from the lower oror even up to 3.2 cm), covering an area of Shivalik Himalayas, (300-1500 m) to higher-31 cm2 and bearing trichomes (56 in ranges of altitude (1500-2400 m, middlenumber) on both surfaces (Kirtikar and Himalayas) to investigate the spread andBasu, 1984; Arora, 1999). Plants have a invasion by A. conyzoides in north-westernshallow tap root system with a radius of India. It was documented that the density ofspread of -8 cm. The plant bears blue-violet weed was greater in the lower Himalayasterminal inflorescence(Fig.5.3) and a compared withthemiddleHimalayas. capitulum of homogamous disc florets (>70 However, the upper Himalayas (2400-3800capitula per plant) arranged in corymbose m) were found to be free of the weed (Dogra,racemes (Kumar and Singh, 1988; Arora, 2008). A survey conducted in Shim la and1999). The inflorescence changes colour Kinnaur (Shivalik hills) showed that A. from blue when young to white at maturity. conyzoides constituted 21.42% of the totalThe number of florets per head varies in the herb species (Rana and Sharma, 2009). range 56-86 (Anonymous, 1988; Table 5.3). Recently,ithasbeenobservedthat The flowering period of the weed is long, infestation by A. conyzoides, along withand flowers retain their violet colour for a Cynodon dactylon and Parthenium hystero-longer period of time. The fruit is a typical phorus,constituted 75%ofthetotalachene with pappus and easily spread by populationinMandhala watershedinwind and animal hair. Seeds are minute (<1 Himachal Pradesh (Rana et al., 2010). cm), black and extremely light in weight, The weed not only invades agricultural/elliptical, bear a pappus, are produced in arablefield,butalsoseverelyinfestsgreat numbers (Table 5.3) and are trans- disturbed sites. Due to its strong competitive ported up to hundreds or thousands of ability and fast propagation, it has covered miles.Arora(1999)reportedthatin all terrain not under intensive use, care andChandigarh, wild-growing plants produce on managed efficiently, and causes significant average5000 seeds. However, Rodriguez ecological damage. Figures 5.1 and 5.2 showand Cepero (1984) reported a total of 94,772 huge monocultures of A. conyzoides onseeds per plant. The weed completes its life wasteland and aroundawheatfield, cycle in about 10-12 weeks, and seeds are respectively. shed, resulting in tremendous increase in

Table 5.2. Distribution of Ageratum conyzoides in different habitats (Chandigarh, India). Density Frequency Dominance Importance value Habitat ( %) ( %) ( %) index (IVI) ( %) Grassland 59.98 22.24 57.96 140.18 Forest 81.73 15.79 83.67 181.19 Water channel 61.94 20.18 60.24 142.36 Wasteland 61.00 21.69 80.10 162.79 62 S. Kaur et al.

Fig. 5.1. Monoculture of Ageratum conyzoides on wasteland.

Fig. 5.2. Ageratum conyzoides around a wheat field. its intensity next season (Bansal and Singh, emerges during the onset of winter and 1986). The propagation of the weed throughremains till early summer. In shady and seeds is so rapid that it covers almostmoisture-rich areas the weed is also seen any terrain not under intensive use orduring the summer rainy season; however, abandoned. Ageratum conyzoides is a shade- in such areas it has a relatively shorter life tolerant plant and flourishes well in any typespan and reduced density (Kohli et al., 2006). of garden soil such as clayey, sandy or loamy with wide range of pH. Soils rich in moisture, minerals and air are best suited to its growth. Invasivepotential of A. conyzoides In hilly tracts of subtropical to temperate environment, the weed is present through-Ageratum conyzoides has become an invasive out the year. However, in the plains, itweed in a wide variety of natural and man- Ageratum conyzoides 63

Table 5.3. Morphological features of Ageratum conyzoides. Parameter Value Shoot height (cm) 82.60 ± 20.29 Radius of spread (cm) 8.01 ± 0.50 Root length (cm) 7.70 ± 0.82 Basal area (cm2) 1.92 ± 0.68 Shoot:root ratio 10.72 ± 3.59 Biomass (g) 3.56 ± 0.20 Trichomes (per cm2) leaf 55.5 ± 11.7 stem 32.0 ± 9.3 Length of leaf petiole (cm) 1.75 ± 0.61 Leaf lamina shape Broadly ovate or rhomboid ovate to triangular length (cm) 7.69 ± 3.24 width (cm) 5.07 ± 2.64 perimeter (cm) 20.81 ± 10.14 area (cm2) 30.54 ± 16.34 transpiration rate (p.g/cm2/s) 79.36 ± 10.21 diffusion resistance (s/cm) 0.046 ± 0.011 relative humidity (%) 44.48 ± 5.96 Peduncle length (cm) 0.64 ± 0.11 colour Sky blue to violet when young, white on maturity Inflorescence type Capitulum made up of homogamous disc florets number 69.00 ± 3.92 diameter of head (mm) 6.1 ± 0.5 number of florets per head 71.50 ± 10.13 Seed colour Black, bearing pappus number 4935.13 ± 77.08 length (cm) 3.4 ± 0.5 width (cm) 0.33 ± 0.01 weight (p.g) 5.06 ± 0.18

made ecosystems ranging from forests and grasslands to farmland.Itisa prolific ephemeral herb with great morphological variations and easily adapts to different ecological conditions (Sauerborn and Kock, 1988). The weed has been recognized as one of the most serious pestsof modern agriculture, one that has encroached on almost all other types of lands, i.e. waste- lands, natural forest, plantations, vegetable gardens,overgrazed pastures,orchards, range/grasslands, riparian zones, ruderal/ disturbedsites,shrub/shrublands,tea orchards, meadows, water courses, fresh landslides or areas with deep gullies and wetlands, and also along roadsides (Kanwar and Kharwara, 1988; Rao, 2000; Kunwar et al., 2001; Kohli et al., 2006; Sankaran, 2007; Fig. 5.3. Inflorescence of Ageratum conyzoides. Batish et al., 2009a, b; GISD, 2010). 64 S.Kau r et al.

Features imparting invasiveness GRASSLANDS.The fast-spreading stolons of A. conyzoides greatly enhance its potential to Attributes for successful invasion of A. coverlargeareasofgrassland.Once conyzoides include: established, the weed displaces and replaces fast growth and rapid spread due tonative grasses/plants and reduces grazing potential to become well established; areas,resultingin fodder scarcity.The wide ecological amplitude; density, diversity and biomass of associated high reproductive potential (both sexualvegetation are severely affected in weed- and vegetative); infested grassland compared with weed-free long flowering and fruiting periods; areas in Chandigarh (Arora, 1999; Table absence of natural predators/enemies/5.2). Furthermore, it reduces the carrying competitors; capacity of pastures, causes thinning of resistance to predators; floraldiversityand may leadtothe unpalatableduetohigh phytotoxindisappearance of threatened and endemic content; and species (Kohli et al., 2004, 2006). resource competition along with novel weapons such as allelopathy. CULTIVATED LANDS.Agriculture ecosystems are most seriously affected by A. conyzoides, ecologically as well as economically. Due to Impacts of A. conyzoides the fast-spreading nature of A. conyzoides, it hinders field practices such as ploughing Different ecosystems and field preparation, thereby increasing the maintenance cost of agricultural fields. It FORESTS.The shade-tolerant nature of A.adversely affects the growth and production conyzoides allows it to become established of major staple annual and perennial crops under tree canopies in developed forests. Itin India (Kohli et al., 2006; Batish et al., has become an aggressive colonizer that can 2009a, b), and forms dense monocultures maintain dense populations within theand interferes with the establishment of understorey duringitsgrowing periodmany crops such as maize, chickpea, rice (Arora, 1999). The tree canopy in forests andand wheat (Kohli et al., 2006; Batish et al., plantations provides favourable conditions 2009a, b). Additionally, it acts as a host for suchasshadeforgrowth.Thetreemany crop diseases (Kashina et al., 2003; plantations of Acacia catechu and Eucalyptus Ekeleme et al., 2005). spp., Pinus forests and mixed-culture tree In the lower Shivalik rangeof the plantationsinthe lower Himalayas ofHimalayas this weed infests cultivated lands Himachal Pradesh have been observed to beto such a serious extent that farmers may occupied by A. conyzoides (Dogra, 2008).have to abandon their fields (Kohli and Native plant species growing in variousBatish, 1996; Batish et al., 2004a). Due to plantations have been facing threats due tothis type of heavy infestation, nothing is left invasion by this exotic weed; this speciesin areas where it has invaded - it is known as was observed as the most frequently andUjaroo (the one that destroys everything) in densely growing under Eucalyptus andthis area (Negi, 1988). mixed-treeplantations(Dogra,2008). Roder et al. (1995, 1998) reported A. Reddy and Pattanaik (2009) reported A.conyzoides as one of the major weeds in rice conyzoides among 64 exotic species posing afields in Asia, causing severe reduction in serious threat to the dense interior forestsrice yield following invasion. It is considered of the Gandhamardan Hill range, Orissa.as one of the worst weeds of paddy fields in The weed was found to encroach on thePokhra (Thapa and Kayastha, 1998) and littoraland swamp forestsof Assam,Kirtipur in (Manandhar et al., 2007). retarding/preventing natural succession and Manandhar et al. (2007) reported reductions reforestation, so much so that some forestsin rice grain (25-47%) and straw (13-38%) have lost their identity (DOEF, 2010). yields due to infestation by A. conyzoides. It Ageratum conyzoides 65

has been reported to be one among theshepherds, orchardists, horticulturists and problematic weeds associated with Gladiolusanimal scientists. cultivation, adversely affecting productivity Once established,itdominates large as well as product quality (Riaz et al., 2007). areas, disrupts nutrient cycles and alters the Many workershaveattributedthepattern of plant succession in the native observed loss in crop produce and quality to ecosystems. Invasion by A. conyzoides results the allelopathic potential of the weed (Singhin negative interactions with native species et al., 2003; Batish et al., 2006, 2009a, b;for food and other natural resources, causing Manandhar etal.,2007; Batish, 2008).extinctionof associated vegetation and However, Ekeleme et al. (2005) opined that thereby declining species richness. Koh li et shoot competition for light may also be oneal. (2004) observed a huge loss in plant of the major causes of its interference withdiversity and density (-50-64%) of native crops. flora after invasion by A. conyzoides in the Shivaliks, North India. The indices of richness and evenness were significantly less in weed- Soil nutrients infested areas compared with weed-free Ageratum conyzoides directly or indirectlyareas,indicating the reduced numerical affectssoil chemistry and composition,strength and uneven distribution of native ecosystem functions and creates a novelflora. Weed-free areas exhibited higher plant environment fornativespecies.Heavydiversity(Shannon'sindex),indicating infestations of the weed modify the soil heterogeneity in the communities. Compared environmentthroughrootexudation,with this, invasion by A. conyzoides resulted affecting soil structure and mobilizing orin a severe loss of plant diversity, and con- chelating nutrients (Singh et al.,2003).sequent homogeneity in communities. On Furthermore, it causes depletion of soil the other hand, the index of dominance was nutrients because of resource competition,higher in areas invaded by A. conyzoides, rendering it unfit for effective growth ofshowing its dominance (occurrence of a crops and making sustainability difficult. single species) in the community (Koh li et al., Manandharetal.(2007)reporteda 2004).Thehomogenousnatureofa significant reduction in soil nitrogen andcommunity leads to instability that further phosphorus in paddy fields due to weedaggravates the potential for invasion by infestation. On the other hand, Batish et al.opportunistic species, especially those with (2009a, b) reported that weed residueswider ecological amplitude. This changing enriched soil nutrient content despite the pattern of vegetation in weed-occupied areas negative effects on crop growth. in comparison with weed-free areas may be attributed to the allelopathic nature of the weed, apart from other factors(Batish, Native vegetation and biodiversity 2008). The Himalayas in India is a global hot spot Dogra (2008) reported adeclinein zone and has an exceptionally high level ofvaluable indigenous medicinal plants such biodiversity. However, the spread of A.as Achyranthes aspera,Trifoliumrepens, conyzoides along with other exotics has Centella asiatica, Zizyphus jujuba, Dichanthium remarkably altered the communities and annulatum,Murrayakoenigii,Adhatoda ecosystem by depleting the indigenousvasica, Carissa spp. and Colebrookea spp. in species (Koh li and Batish, 1996; Koh li et al.,the Shivaliks of Himachal Pradesh (India) 2006; Dogra et al., 2009a, b). Invasion offollowing invasion by A. conyzoides. Some A. conyzoides is a matter of serious concern, species such as Sonchus oleraceus, Sonchus as it causes a reduction in niche or habitatas per, Vernonia cinerea, Abutilon indicum, for growth and establishment of valuableAgave americana and Medicago lupulina were plants. In fact, the, rapid spread of thisnot found in weed-infested areas, while they exotic is a serious concern for foresters,were found to be growing abundantly in farmers, ecologists, environmentalists,weed-free areas (Dogra, 2008). 66 S.Kau r et al.

Batish (2008) revealed that A. conyzoidesthe Western Ghats (Swamy et al., 2000) and causes reduction in growth of other grassesthe Mudumalai wildlife sanctuary (Silori and and weeds measured in terms of dry biomass Mishra, 2001) have been observed to be (up to 50%) and total number of species (upinfested by A. conyzoides. to 30%). Its dense monoculture-forming growth habit places it in the category of invasive species that can transform the Humans and animals integrity of community and ecosystemsNot only does A. conyzoides affect farmers visually, structurally and chemically. A recent and scientists, but it also has adverse effects study showed that -20% of the vegetationalon human and animal health. People in area in the lower Shivalik Hillsof thecontact with this weed suffer from nausea, Himalayas was occupied by A. conyzoides,giddiness, irritation and asthma (Kohli and along with other invasive plants; however, Batish,1996;Negi andHajra,2007). this weed accounted for -30% reduction inLivestock do not feed on it as it causes plant species (Dogra et al., 2009a, b). ulceration and toxicity. Dogra et al.(2009b) investigated the impact of invasion by A. conyzoides along with other invasive species on the structure Role of allelopathy in invasion potential of and composition of communities in the A. conyzoides lower Himalayas. Following weed infest- ation, alpha diversity was reduced by -40%.Allelopathy is a type of biotic interference in The number of abundant and very abundantwhich plants release bioactive molecules species, index of evenness, and fresh and dryinto the surrounding environment and that biomass of vegetation were also drasticallynegatively affects the growth of nearby reduced in areas infested by A. conyzoidesvegetation. In fact, allelopathy has been compared with weed-free areas. All theseadopted as a successful strategy for the observations show the homogenous naturespread,establishment,domination and of the ecosystem and loss of productivity incolonizationofalienenvironments by weed-infested areas (Dogra et al., 2009a, b).invasive weeds, thereby replacing native Furthermore, fresh and dry biomass wasvegetation (Bais et al., 2004; Kohli et al., also reduced in A. conyzoides-infested areas2004, 2006; Hao and Qiang, 2005; Batish, compared with weed-free areas, thus making2008). A number of aggressive weeds have those areas less productive (Dogra et al.,been reported to exhibit allelopathy as a 2009a, b). Ageratum conyzoides has also beenmechanism of interference, which provides reported as being among the three mostthem competitive advantage over other invasive weeds that have altered the com-plants (Qasem and Foy, 2001). Ageratum munity structure and population dynamics conyzoides has been reported to have adopted of native flora and fauna in the Shivalik Hillsallelopathy as a strategy to out-compete (Rana and Sharma, 2009). Recently, it hasnative flora and suppress growth of crops. been reported that the undesirable effects ofThereismuch evidence regarding the A. conyzoides - along with those of otherallelopathic nature of A. conyzoides providing plants-resultedinunevenness andit with selective advantage (Kong et al., instability of herb layers in the Mandhala1999; Batish et al., 2009a, b). It has been watershed in Himachal Pradesh (Rana et al., demonstrated that root and shoot aqueous 2010). extracts of A. conyzoides are phytotoxic to Even the reserve parks/wildlifeseed germination and seed vigour in maize sanctuaries/protected areas have also beenand soybean (Singh et al., 1989) and to observed to be affected by this weed,growth in wheat and rice (Jha and Dhakal, resulting in disruption and loss of natural 1990; Prasad and Srivastava, 1991). Acetone vegetation; for example, the Jim Corbettextracts of A. conyzoides shoot residues tiger reserve (Rawat etal.,1997), theinhibited the germination and growth of Veerapuli and Kalamalai forest reserve inroots and shoots of Amaranth us caudatus, Ageratum conyzoides 67

Digitariasanguinalis and Lactucasativawas observed in response to volatile oils (Kato-Noguchi, 2001). compared with pure constituents, thus Leaf debris and even soil entangled withdemonstrating the synergisticeffectof the roots of A. conyzoides (rhizosphere soil)allelochemicals (Kong et al., 1999). Further- were also observed negatively to affect roots,more, the allelopathic potential of the weed shoot length and biomass accumulation inis enhanced when plants are grown under rice by -18-30% (Batish et al., 2009a). Apart stress conditions such as nutrient deficiency from living tissues, leftover residues collected (Kong et al., 2002). at the end of the growing season in the area of weed invasion also interfered with maize and rice (Batish et al., 2004b). However, the Phytochem istry allelopathic potential of A. conyzoides varies depending on organ, developmental stage SinceA.conyzoidespossessesdiverse and habitat (Hu and Kong, 1997). biological and physiological characteristics it Soil inhabited by the weed has beenhas been explored intensively, particularly reported to be rich in non-volatile allelo-for its secondary metabolites (Gonzalez et chemicals (Singh et al., 2003) and to beal. 1991; Wiedentold and Roder, 1991). A phytotoxic to growth of other plants. Radiclewide range of secondary metabolites from and coleoptile lengths of crop plants weredifferent classes are found in A. conyzoides, severely suppressed when grown in field soilincluding flavonoids, alkaloids, chromenes, previously infested with A. conyzoides (Kalia, phenolics and essential oils (Gonzalez et al., 1998; Singh et al., 2003). This may have been 1991; Sharma and Sharma, 1995). Among due to water-soluble phytotoxins present inthese secondary metabolites, many are A. conyzoides that interfere with the processallelochemicals and inhibit the growth of of nutrient uptake (Batish, 2008; Batish etother organisms (Pafi et al., 1998; Okunade, al., 2009a, b). 2002). These allelochemicals are released Batish et al. (2006) demonstrated theeither through leaching or volatilization into allelopathic effect of A. conyzoides againstthesoilorenvironmentinbioactive chickpea and observed a severe reduction inconcentrations, and retard the growth of the number of nodules, nodule weight andother plants and organisms (Singh et al., the leghaemoglobin content of the nodules 2003; Batish et al., 2009a, b). of chickpea grown in soil amended with weed residues. Later, it was found that weed- infested soil and leaf extracts deleteriously Volatile compounds affected the growth of rice, which wasAlmost every part of a plant contains volatile attributed to water-soluble phytotoxins, i.e.oils; the leaves and roots of A. conyzoides phenolics (Batish et al., 2009a). Leaves werecontain volatile oils in the range of 0.11 - demonstrated to exhibit a greater inhibitory 0.58% and 0.03-0.18%, respectively, effect than stems and roots (Xuan et al.,depending on the season (Wandji et al., 2004). 1996). As many as 51 constituents, including Even the extracts of isolated and purifieda number of mono- and sesquiterpenoids, precocene I and II, the major chromenes ofhave been identified from its volatile oils A. conyzoides, also possessed allelopathic (Okunade, 2002). The chromenes 7-methoxy- potential towards tomato, ryegrass and2,2-dimethylchromene (precoceneI),6,7- radish (Kong et al., 1998a, b). Kong et al.dimethoxy derivative, ageratochromene (1999, 2002) demonstrated that volatile leaf(precocene II) and their derivatives (Burkill, oils from A. conyzoides inhibited seedling 1985; Rastogi and Mehrotra, 1990; Kissmann growth and reduced the chlorophyll contentand Groth, 1993; Kong et al., 1998a, b) are of Cucumis sativus, Lolium ultiforum , Raphanus the major constituents of leaves and flower sativus, Phaseolus aureus, Triticum aestivum oils, and possess biological activities (Bowers and Lycopersiconsp.Greaterinhibitionetal.,1976).Theseallelochemicalsare 68 S. Kau r et al.

released from A. conyzoides, accumulate in the Medicinal value soil with the passage of time and were found Ageratum conyzoides is an integral part of to be responsible for growth suppression oftraditional medicine in many countries of weeds and reducing the population of soil- borne pathogenic fungi in intercroppedworld, particularly in tropical and subtropical regions. The extracts and metabolites of A. citrus orchards (Kong et al., 2004). Kong et conyzoides have been used as a bacteriocide, al. (1999, 2002) demonstrated that freshantidysentric and antilithic (Borthakur and leaves and volatileoilsof A. conyzoides Baruah, 1987; Okunade, 2002) by traditional exhibited adverse effect on crops, and they communities in India, South America and attributed this to the presence of precocenes Africa. In Central Africa, Brazil and Congo it and theirderivatives,i.e.precoceneI, is used to cure pneumonia, wounds and precocene II, 3,3-dimethyl-tert-butylindone and 13-caryophyllene, and several mono-burns (Ming, 1999). Its decoction is given to treatheadache, terpenes and sesquiterpenes. fever and rheumatism (Kirtikar and Basu, 1984; Okunade, 2002). A crudematerial from leavesofspecies possessesinvitroantibacterialactivity Non-volatile compounds against Staphylococcus aureus and is also In addition, A. conyzoides is very rich in poly-used for wound healing (Durodola, 1977). In oxygenated flavonoids such as kaempferol, Cameroon, aqueous extracts of the whole quercetin and their glucosides, and smallplant are known for their anti-diabetic quantitiesof triterpenoids andsterolsproperties (Tsabang et al., 2001). (Okunade, 2002). A number of phenolic acids such as gallic, coumalic, protocatechuic, Insecticidal /bactericidal /antifungal value benzoic,sinapic,p-hydroxybenzoic and coumaric acid have been reported as active Theoilobtained fromitsleaves and compounds in A. conyzoides (Xuan et al.,inflorescence has insect-repellent properties 2004). Batish et al. (2009a, b) reported the (Saxena et al., 1994; Nogueira et al., 2010). non-volatilecomponentscate chinandTraditional communities in Asia, South phenolic acids (gallic acid, coumalic acid,America and Africa use the aqueous extracts protocatechuic acid and p-hydroxybenzoicof the species as a bactericidal (Borthakur acid) from leaves and soil inhabited by theand Baruah, 1987; Ekundayo et al., 1988). weed. However, the level of allelochemicals Leaf volatile oils of A. conyzoides have been and hence allelopathic potential dependsreported to kill the maize grain weevil, upon the growth stage and type of habitatSitophilus zeamais (Bouda et al., 2001). The (Kong et al., 2004). Its seeds have also beenweed has also been reported to have natural known to yield fatty oils (Ambasta, 1992). fungicidal potential (Pu et al., 1990; Gravena These allelochemicals show a synergisticet al., 1993). effect, and their allelopathic potential is intensified on exposure to various environ- Herbicidal value mental stresses (Josep and Joan, 1997; Kong et al., 2002; Batish et al., 2009a, b). Ageratum conyzoides has been reported as a natural herbicide for weed control in paddy fields (Xuan et al., 2004). Application of A. conyzoides at 2 t/ha served as an effective Uses of A. conyzoides herbicide in controlling paddy weeds such as Echinochloa crus-gallivar. formosensis, Although this weed is becoming a seriousMonochoria vaginalis var. plantaginea and concernforfarmers,horticulturalists,Aeschynomene indica. Ramakrishna etal. foresters, land managers, ecologists and (2006) reported that a mulch of A. conyzoides environmentalist, the plant also has somehad good potential in checking the growth useful aspects, including the following. of weeds and enhancing crop yield. Ageratum conyzoides 69

Others 2,4,5-T provides excellent control of this A mulch of A. conyzoides has been reportedweed (Rao, 2000). However, due to toxico- to prevent loss of soil moisture and reducelogical implications, synthetic herbicides are erosion (Ramakrishna et al., 2006). It cannot recommended as a good method of serve as good biological waste for thecontrolling A. conyzoides. preparation of manure and biogas. Dried plant material from A. conyzoides is used for Field and crop management pest control (Vallador et al., 1994). Ageratum conyzoides planted as a riparian wetlandTo optimize weed control, farmers are herb on the banks of the Rihand River inrequired to know the time of emergence of Renukoot plays a positive role in reducingweed seedlings relative to the crop, apart erosion of organic carbon and cationicfrom any use of commercial herbicides nutrients and helps in soil conservation(Ekeleme et al., 2005). In northern Laos, (Kumar et al., 1996). Recently, it has been increased fallow periods in slash-and-burn observedthatA.conyzoideshelpsinrice production systems have resulted in maintaining the texture and fertility of soilreduced weed infestation (Roder etal., along the River Damodar riparian zone in1998). Bhowra, as soil erosion was minimized to a great extent following its planting compared with bare areas (Srivastava et al., 2009). Ecological methods The use of eco-friendly compounds such as natural plant products and other plant- Control/management of A. conyzoides based formulations offers a safer strategy for effective weed control. Volatile mono- To date, a number of strategies includingterpenes such as cineole and citronellol have physical, chemical and ecological methodsbeen found to have considerable effects on have been tried, though none has beengermination, growth, chlorophyll content found completely to control or manage theand cellular respiration of A. conyzoides, weed. suggestingmuchpotentialforweed management (Singhet al., 2002a). A study conducted by Batish et al. (1997) and Physical methods Singh et al. (2002b) revealed that parthenin, These include manual uprooting, mowing,a sesquiterpene lactone from Parthenium cutting with machete or burning of live hysterophorus, negatively affected the growth plants. In general, these are of some useand physiology of A. conyzoides and has when the plant is at the vegetative stage.potential for use as a novel agrochemical. However, certain limitations are associated with these methods, for example the high cost of labour, ill-effects on workers' health, Role of community vegetative regeneration from stolons, etc.The methods outlined above cannot achieve (Batish et al., 2004a). Furthermore, at thesuccessful weed control and management maturity stage, uprooting of plants resultson their own; an integrated approach, in dispersal of seeds to other areas. incorporating all the above approaches, is essential. Furthermore, fallow lands likely to be invaded by the species should be put to Chemical methods some use such as planting of native grasses Pre-emergence application of commercialand fodder. To this end, local communities herbicidessuchasatrazine,diuron,play a significant role (Anonymous, 2003). methazole, metribuzin or simazine is anLocal populations need to learn about effective control strategy. For establishedenvironmental issues, the ecological hazards infestations, the application of 2,4-D andof A. conyzoides and the identification of the 70 S. Kaur et al.

speciesso that it may be uprooted at an early vegetation, soil and microbial biomass. Forest stagebeforeitspreads.Furthermore, Ecology and Management 159,231-239. organic compost and vermicompost may be Bais, H.P., Park, S.-W., Weir, T.L., Callaway, R.M. useful to control and manage the weed and Vivanco, J.M. (2004) How plants (Batish et al., 2004a). communicate using the underground informationsuperhighway.TrendsinPlant Science 9,26-32. Bansal, G.L. (1988) Weed biology of Lantana and Conclusions Ageratum spp. In: Negi, G.C. and Singh, C.M. (eds) Proceedings of Seminar on Control of From the above discussion, we conclude Lantana and Ageratum Species.Himachal that Ageratum conyzoidesis one of the Pradesh Agriculture University, Palampur, India. most harmful exotic weeds in a wide variety pp. 10. of habitats and adversely affects many Bansal, G.L. and Singh, C.M. (1986) Effect of herbicidesoncontrolandgerminationof facets of ecosystem function.Theweed Ageratum conyzoides. Indian Journal of Weed possesses many physiological, ecological and Science 18,254-256. morphological features that help inits Batish,D.R. (2008)Tropical American Invasive successfulinvasion.Therefore,efforts Weeds in the Shiwalik Range of North Western should be made to manage this weed through Himalayas of India: An Assessment of Status an integrated approach involving different and Impact. Available onlineathttp,//www. management strategies in combination with apafri.org/forestHealth08/DAY2_Forest%20 community participation. Health°/020Workshop/Daizy_APAFRI_DAIZY_ Malaysia-1.pdf (accessed 18 October 2009). Batish, D.R., Kohli, R.K., Singh, H.P. and Saxena, D.B. (1997) Studies on herbicidal activity of References parthenin-a constituent of Parthenium hysterophorus towards billy-goat weed. Current Akter, A. and Zuberi, M.I. (2009) Invasive alien Science 73,369-371. species in Northern Bangladesh, Identification, Batish, D.R., Singh, H.P., Kohli, R.K., Johar, V. and inventory and impacts. International Journal of Yadav,S. (2004a) Management of invasive Biodiversity and Conservation 1,129-134. exotic weeds requires community participation. Ambasta, S.P. (1992) The Useful Plants of India. Weed Technology 18,1445-1448. National Institute of Science Communication, Batish, D.R., Singh, H.P. Kaur, S., Arora, V. and Delhi, India. Kohli, R.K. (2004b) Allelopathic Interference of Anonymous (1986/87) Annual Report of the All- residues of Ageratum conyzoides. Journal of India Coordinated Research Project on Weed Plant Disease and Protection XIX, 293-299. Control. Himachal Pardesh Krishi Batish, D.R., Singh, H.P., Kaur, S. and Kohli, R.K. Vishavvidhalya, Palampur, India. (2006) Phytotoxicity of Ageratum conyzoides Anonymous (1988) The wealth of India - raw residues towards growth and nodulation of materials. Publications and Information Cicer arietinum. Agriculture Ecosystems and Directorate, Council of Scientific and Industrial Environment 113,399-401. Research, New Delhi, India. Batish, D.R., Kaur, S., Singh, H.P. and Kohli, R.K. Anonymous (2003) Report of Two-day Workshop (2009a) Role of root-mediated interactions in on the Management of Weeds (Congress grass, phytotoxic interference of Ageratum conyzoides Lantana, Neela Fulnu) through Community with rice (Oryza sativa). Flora 204,388-395. Participation, 25-26 March 2003. State Council Batish, D.R., Kaur, S., Singh, H.P. and Kohli, R.K. forScience,Technology andEnvironment, (2009b) Nature of interference potential of leaf Shimla, India, pp. 2-3,16. debris of Ageratum conyzoides. Plant Growth Arora, V. (1999) Comparative assessment of eco- Regulation 57,137-144. physiologicalfunctionsbetweenAgeratum Batta, J.N. (1988) Lantana camara (Baraphulnu) - conyzoides L. and Parthenium hysterophorus L. a threat to grazing and pasture land in Mid-Hill. PhD thesis,PanjabUniversity,Chandigarh. In: Negi, G.C. and Singh, C.M. (eds) Proceedings India. of Seminar on Control of Lantana and Ageratum. Arunachalam, A. and Arunachalam,K.(2002) Himachal Pardesh Krishi Vishavvidhalya, Evaluation of bamboos in eco-restoration of Palampur, India, pp.1-3. 'jhum' fallows in Arunachal Pradesh, ground Bentham,G.(1861)FloraHongkongensis: A Ageratum conyzoides 71

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