The Problem of Chromolaena Weed

by
S.R. Ambika and Jayachandra
Lecturer, Department of Botany, Bangalore University,
Bangalore, 560056, India

 References


Chromolaena odorata (L.) King and Robinson, an allohexaploid member of Asteraceae, is a native of South and Central America but has thoroughly naturalized in parts of Africa, India, Sri Lanka, Indochina, Malaysia and Indonesia. It is a herbaceous perennial growing to a height of three meters in open situations and up to eight meters in the interior forests where it assumes a scrambling habit (Bennett and Rao, 1968; Rai, 1976; Ambika and Jayachandra, 1980a).
The botany and the Phenology of the species have been described by King and Robinson (1970), Salgado (1972) and Rai (1976).
The distribution of Chromolaena is limited to warm and humid tropical regions, latitudes about 30°N and S, and an altitude of about 1000m near the equator. It thrives in the regions with rainfall of 200cm and above per annum and temperature range of 20° to 37°C. Its spread extends from Western ghats in India to the Philippines in Asia and the Marianas and Caroline Islands in the Western Pacific (Muniappan and Marutani, 1988). It has now become a serious weed in Bhutan, Nepal, China, Indonesia, Sri Lanka, Nigeria, India, Malaysia, Mariana Islands and Caroline Islands.
The occurrence of this weed in India was first reported by Rao (1920). Having the ability to spread fast and being a good coloniser in the newly introduced areas, the species is now a menace in the estates of Assam, Karnataka, Kerala, Maharastra, Orissa, Tamil Nadu and West Bengal (Moni and George, 1959; Rai, 1976; Ambika and Jayachandra, 1980b) and is known by various local names in different countries (Rai, 1976; Muniappan and Marutani, 1988).
Precipitation, temperature and light intensity control the distribution and spread of this species. Light promotes its germination but does not become a limiting factor; however, it has tremendrous impact on the vegetative phase of growth and establishment of the species thus explaining its absence in closed plantations and thick estates (Ambika and Jayachandra, 1980a).
C. orodrata grows as an aggressive coloniser in different habitats - like areas cleared for developing new plantations, nurseries, young and open plantations, agricultural fields, pasture lands, fallow fields, waste lands, road sides, river banks, tree tops, thatched roofs, rocky areas, slash and burnt areas (Chakrabarthi et al; 1967; Soerohaldoko, 1971; Salgado, 1972; Ivens, 1973, 1974; Rai, 1976; Yadav and Tripati, 1979; Mishra and Sharma, 1979; Ambika and Jayachandra, 1980b) in different parts of the world.
This weed does not cause any serious concern in its native land (Cruttwell, 1988); however, it is posing grave problem in the plantations of teak, rubber, coffee, soft wood, oil palm, coconut, cashew, mango and others depressing their growth, development and yield (Salgado, 1972; Ivens, 1973; Ambika and Jayachandra, 1980b, 1982; Muniappan and Marutani, 1988), agricultural crops (Puckdeedindan, 1966; Esuruoso, 1971; Napompeth, Hai and Winotai, 1988; Muniappan and Marutani, 1988) and causes serious health hazards to the live stock and human beings (Soerohaldoko, 1971; Sajise et al., 1972, 1974; Aterrodo and Talatala -Sanico, 1988) in parts of Bhutan, Nepal, China, Indonesia, Sri Lanka, Nigeria, Malaysia, India and in the Mariana Islands.
In the coconut plantations of most districts of Sri Lanka, Chromolaena competes with the palm so severely as to result in poor setting of female flowers and premature abscission (Salgado, 1972). In South Africa, the weed is reported to compete for natural resources suppressing the indigenous vegetation (MacDonald and Jarman, 1985). In the Philippines, this weed poses danger not only to crops like coconut, corn, sweet potato, cassava, sugar cane and rice but also invades open fields and pasture lands frequently forming an impenetrable pure strand, excluding all forage species (Sajise et al., 1972, 1974). In Indonesia, the continuous invasion of the grazing land by the weed resulted in the reduced grazing facilities of the banteng (Soerohaldoko, 1971).
In India, Chromolaena is a menace in the plantations of teak, rubber, cardamom, arecanut, coconut, citrus and tea in the states of Assam, Kerala and Karnataka (Moni and George, 1959: Rai, 1976; Ambika and Jayachrandra, 1980b, 1982). In the Karnataka state, the authors have observed heavy infestation of this weed in the malnad parts (hilly tracts ) of Shimoga, Thirthahalli, Hassan, Madikeri, Kakanakote, Nagarahole, Subramania and Sullia reportedly causing great loss to the plantation and timber. Chromolaena grew in pure stands covering vast hilly areas where natural vegetation was cleared for developing plantations, waterlands and road sides (plate-1).
It grew very luxuriantly with teak plants of all stages of growth; the teak nurseries looked like that of C. odorata (plate-2), having a few impoverished, sickly young teak plants. In forest land freshly cleared and planted with teak and soft wood seedlings, Chromolaena smothered the crops completely (pate-3). In slightly older plantation with open canopy, these overtopped the teak leaving them slender and narrow with a few leaves (plate-4); but in the established plantations with completely closed canopy, it was confined to the outskirts. A few that could survive in the interior of the plantations, developed a straggling habit sending their branches atop the trees (plate-5).
At Sampaje and Sullia (Kakshina Kannada region) Chromolaena was found to infest young and open rubber plantations (plate-6), but in the old and well established ones, it was found again only along the border. Chromolaena found its way very easily into the plantations of arecanut (plate-7), banana and coconut (plate-8) which provided partly open conditions. In Eucalyptus plantations, it was confined to the borders (plate-9). However, in Bangalore (plains) this weed is seen only in isolated patches.
Despite regular weeding operations by the Karnataka Forest Department, Chromolaena found its way very easily into the plantations of arecanut (plate-7), banana and coconut (plate-8) which provided partly open conditions. In Eucalyptus plantations, it was confined to the borders (plate-9). However, in Bangalore (plains) this weed is seen only in isolated patches. Despite regular weeding operations by the Karnataka Forest Department, the Chromolaena problem has remained very much unsolved.
This weed is also a serious problem in the agricultural lands. The large number of light, anemochorus cypsella of the species that are easily disseminated over a wide area carry a number of seed borne fungi - like Fusarium culmorum, F. moniliforme, F. semisecturm and F. solani infecting 15 to 60 precent of seed population, Clasdosporium herbarium in 22 to 75 percent; many of these fungi have been reported as pathogens of food crops (Esuruoso, 1971). In Thailand, the weed has been reported to be an alternate host of the leaf spot Cercospora sp. (Puckdeedindan, 1966). Chromolaena is also known to serve as an alternate host plant for various aphid species, most of which are known as crop pests and vectors of plant pathogens (Napompeth, Hai and Winotai, 1988). Besides these, C. odorata is known to harbour a number of insects and mites injurious to other crops in Asia (Muniappan and Marutani, 1988).
In the forests of Ripponpet (Shimoga, Karnataka), Chromolaena formed big bushes that provided hiding places for wild boars, bandicoots and elephants, which destroyed the agricultural crops in the neighborhood (plate-10).
The weed is poisonous to livestock as it has exceptionally high level of nitrate (5 to 6 times above the toxic level) in the leaves and young shoots; the cattle feeding on these die of tissue anoxia (Sajise et al., 1974).
Hand weeding of Chromolaena reportedly caused skin allergy in a number of plantation workers of Shimoga District of Karnataka and the dry stumps left after the weeding operation caused poisonous wounds in the feet of workers.
The dry plants of the weed in the plantations and vacant land constituted a serious fire hazard in most areas of Asia and the Western Pacific. Fire destroys most of the upper parts of Chromolaena bush, leaving the basal clump unaffected. These clumps regenerate shoots in the rainy season enabling the species to become the first dominant in the next growing season (Liggitt, 1983).
Chromolaena is found to be endowed with allelopathic potentialities, the leaves having the maximum amount of allelochemicals; the impoverished growth of the young teak and other timber plants in the nurseris and young plantations could be at least partly allelopathic (Ambika and Jayachandra, 1980b, 1982).
Studies have been carried out in different laboratories all over the world for controlling the weed by cultural, herbicidal and biological methods. Mechnical and chemical methods are reported to be effective in controlling the weed only temporarily because of the quick reinfestation of the cleared areas by the vegetatively reproduced shoots from the stubles and these methods become prohibitively expensive besides other limitations (Sheldrick, 1968; Ivens, 1972, 1974; Salgado, 1972; Nair, 1973; Olaoye, 1974a; Rai, 1976, 1976 and Erasmus, 1988).
Biological control trials also proved unsatisfactory (Bennett and Rao, 1968; Cruttwell, 1970; Giriraj and Bhatt, 1972; Hall et al., 1973; Olaoye, 1974b). The legumes like Pueraria phaueoloides, P. javanica, Centrosema pubescens, Tephrosia purpuria, Calopogonum caerulum, Desmodium ovalifolium and Moghania macrophylla that have been used as cover crops in plantations was found to loose in competition with this weed and in certain cases they proved to be more troublesome then Chromolaena (Salgado, 1972; Rai, 1976). Thus, even after several years of research, problem of controlling Chromolaena has remained unsolved. Only a judicious integrated approach involving all the known methods of weed control could prove useful in reducing the magnitude of the Chromolaena problem in different situations, considerably.

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