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   Ageratum conyzoides (herb)
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    Details of this species in India
    Status: Alien
    Invasiveness: Invasive
    Occurrence: Established
    Source: Batish et al. 2004
    Arrival Date:
    Introduction: Intentional, legally
    Species Notes for this Location:
    Ageratum conyzoïdes, an annual invasive weed from tropical America, has now naturalised worldwide, particularly in South East Asia, including India, China, Japan, Indonesia and Korea (Kohli et al.2006, Kong et al. 2004, in Batish et al. 2009a). In India A. conyzoides was introduced in 1860 as an ornamental plant; later it escaped as a weed in various habitats throughout India (National Focal Point for APFISN, India, 2005, in Dogra et al. 2009). In India, it is a common weed of croplands, rangelands, pastures, plantations, grasslands and also invades forests where it seriously affects the medicinally important understory herbs (Kohli et al. 2006, in Batish et al. 2009a). It is also a common weed in tea plantations in NE and S India (Rao 2000). In hilly tracts of north western India, it grows up to an altitude of 1800 meters (Singh Undated).

    In India, exotic weeds, especially Parthenium hysterophorus in urban areas, Lantana camara in forestlands, and Ageratum conyzoides in croplands, have assumed the proportion of noxious biological pollutants. Each of these three natives of tropical America has wide ecological amplitude (wide range of tolerance). Ageratum conyzoides is primarily a weed of agricultural land. However, it is also fast encroaching upon grasslands, pastures, and even the forest understory (Kohli 1997, in Batish et al. 2004). A. conyzoides is naturalised and posing a threat to agro- as well as urban ecosystem. Its aggressive regenerative and reproductive potential, apart from other characters enable its quick spread and colonisation (Kohli & Batish 1996).

    Management Notes for this Location:
    The fast spread of devastating exotic weeds such as A. conyzoides is a matter of serious concern because they spread at the exclusion of native plants and local biodiversity. Because of this the Indian state and union governments have been trying hard to assess the damage and find a solution for the control of these prominent invasive weeds. To manage these noxious weeds, a number of strategies have been tried with little success. Considerable resources are being allocated to top research and development projects involving integrated management. Batish and colleagues (2004) discuss the obstacles towards control measures and propose that success in management could be achieved through community mobilization.

    Physical: Physical methods tried with little success include: mowing (at tender stage), manual uprooting, cutting with swords, use of shrub-masters for heavily infested areas followed by burning or burning live plants. These methods are useful only at the vegetative stage and are labor intensive and pose a risk to human health. Once the plant matures (starts producing seed) physical removal becomes only a short-term solution (Batish et al. 2004).
    Chemical: A number of synthetic herbicides have been tried for the management of these weeds such as atrazine, alachlor, paraquat, glyphosate, simazine, 2,4-D, and 2,4,5-T. The effective dosage required varies with the growth stage. Although herbicides are quite effective in providing immediate control the weeds soon reappear because of quick regenerative potential. Repeated use of herbicides comes with toxicological concerns (Batish et al. 2004).
    Integrated Land Management: Batish and colleagues (2004) advocate integrated land management as the best strategy forward. After clearing infested areas land should be put to some use, with community input as a priority. Motivation should stem from education, with people becoming aware of the hazards of these weeds. Identification methods should be taught to school children, farmers and the general public. The involvement of non-governmental organizations and eco-task forces is also important. Educational awareness should focus on weed identification and life-cycle, motivation for the effective removal of the weed at an early growth stage and management of waste through vermi-composting.
    Efforts to manage A. conyzoides through eco-friendly means tried are also discussed in Kohli and Batish (1996).

    Location Notes:
    Agricultural: A. conyzoides interferes with crops and causes yield reductions of major staple crops of India (Kohli et al. 2006). It forms thick monospecific stands at the expense of commonly grown crop species such as wheat, chickpea, rice and maize (Kohli et al. 2006, in Batish et al. 2009a). When it invades rangeland areas, it out competes native grasses causing scarcity of fodder (Kohli et al. 2006), thereby putting livestock under starvation conditions. Severe infestations by A. conyzoides reduces crop yields significantly and to such a low level that some farmers in the lower Shivalik ranges of the Himalayas have had to abandon their fields (Batish et al. 2004; Kohli & Batish 1996).
    Other: A. conyzoides poses a human health hazard also (Kohli & Batish 1996). A number of health problems in human beings and toxicity to livestock have been reported. These include contact dermatitis, skin irritation, nausea, giddiness (due to their pungent smell), and respiratory problems such as bronchitis and asthma.
    Reduction in native biodiversity: Rich medicinal plants, an important resource, are being out-competed by A. conyzoides (Kohli & Batish 1996).
    Last Modified: 27/11/2009 12:08:14 p.m.

ISSG Landcare Research NBII IUCN University of Auckland