Integrated management: Experts recommend that future work on invasive plant species in the Shiwaliks in the Himalayas take an IPM approach. The problems associated with invasive species are aggravated due to lack of awareness, insufficient information on the species and its dimensions of the spread (Dogra, Kohli & Sood 2009). Batish (2008) recommends the compiling of comprehensive information on the invasive plant species, determining their possible modes of entry, understanding the biological and ecological attributes of the invasive plants, determining the socio-economic and ecological impact of the invasive plants in the area and disseminating this information to the general public and devising preventive measures for areas free of invasive weeds.
Chemical: Pre-emergence application of simazine, atrazine, diuron, oxadiazon, oxyfluorfen, methazole or metribuzin provides excellent control of this weed. Post-emergence application of 2.4-D controls established infestations (Rao 2000).
On the other hand eco-based, environment-friendly strategies for the effective control of A. conyzoides are suggested. Plant extracts of parthenin and eucalyptus (volatile essential oils) may hold promise in controlling A. conyzoides (Batish et al. 1997, Singh et al. 2002, in Batish et al. 2004) and some success has already been achieved using these and other natural plant extracts. For example, a study on the allelopathic effect of two volatile monoterpenes (cineole and citronellol) on A. conyzoides has revealed their potential for future weed management. Both the monoterpenes severely affected the germination, speed of germination, seedling growth, chlorophyll content and respiratory activity of A. conyzoides and after two weeks of exposure, the weed plants wilted. Cineole was the more toxic of the two monoterpenes (Singh Batish and Ravinder 2002).
The addition of activated charcoal, an inert material with high affinity for organic biomolecules, partly ameliorates the negative effects of A. conyzoides phenolic allelopathic root residues on rice (Oryza sativa) growth (Batish et al. 2009).
Field and crop management: Increased fallow length in slash-and-burn rice (Oryza sativa L.) production systems of northern Laos decreases weed pressure (Roder et al. 1998). Compared with continuous rice treatments treatments with fallow or cowpea (Vigna unguiculata) in the previous year had 32% less herbaceous weed biomass and 90% fewer A. conyzoides.
The timing of weed seedling emergence relative to the crop is important in planning and optimizing the time of weed control. Ekeleme and colleagues (2005) have predicted seedling emergence of tropical weed species, specifically in low-input and small-scale farms. To control weeds adequately, especially with limited use of herbicides, farmers need to know the timing and extent of weed seedling emergence before and during the growing season. Knowledge of when weeds emerge is equally applicable and beneficial to all forms of weed-management technologies (see: Ekeleme et al. 2005).
Research: To respond effectively to invasive species problems quantitative measurements of the impact of invasion on biodiversity are required (Schooler et al. 2006, in Dogra et al. 2009).
Location Specific Management Information
To address this problem effectively, public awareness about invasive species have to be developed and participatory approach to control the invasive weeds adopted. Students, researchers and the public should understand the risk and impact associated with invasive species and should be motivated to work for eradication of these noxious plants controlling their reproduction and spread. The government, policy makers, the local and national/international NGOs, and the media should be aware of this grave risk and act accordingly.
Extensive search for yet undiscovered weed hosts of Tomato yellow leaf curl Tanzania virus is advocated, and the practice of farm sanitation is encouraged to eliminate reservoirs of the virus and vector.
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).
Research: Work by Dogra and colleagues (2009) was carried out to find the intensity of invasion (dominance, density, abundance, frequency and importance value index) of these three significantly invasive species (A. conyzoides, L. camara, P. hysterophorus) in the lower Shivalik hills and to understand the impact of invasive plants on the structure and composition of other species. Their results showed that more than 20% vegetational area in lower Shivalik hills is covered by these three invasive species. The authors also found that the number of plant species is highly reduced in the areas invaded by these weeds and that the decrease was 30% for A. conyzoides. Similarly, Margalef index of species richness was also decreased by 36%. The index of dominance increased by 53% in the Ageratum invaded areas. The higher value of this dominance index among the invaded plant communities predicts the homogenous nature of the vegetation. The a-diversity of vegetation was drastically reduced due to the invasion of these three plant species in Shivalik hills (40% for Ageratum) Likewise, the number of abundant species (N1) and very abundant species (N2) and index of evenness were also significantly decreased in the areas invaded by these three invasive plant species. The comparison of the fresh and dry biomass of vegetation between the invaded and un-invaded areas also shows the decrease in productivity of communities in the invasive invaded areas.
Medicinal plants, including Acyranthes aspera, Dichanthium annulatum, Murraya koenigii, Adhatoda vasica, Carissa spp. and Colebrookea spp., declined in areas invaded by A. conyzoides (Singh Undated). There is an urgent need for the management of indigenous or medicinally valuable plants in the invaded areas under their natural habitats (Dogra et al. 2009).
Factors considered to contribute to the invasiveness of A. conyzoides are (Singh Undated): Fast growth rate; Unpalatable or bitter tasting - rich chemistry; Long flowering and fruiting periods; Very high seed production; Adaptability and wide ecological amplitude; High regenerative potential; and Absence of natural enemies / competitors.
1. Batish, Daizy R., Kaur, Shalinder, Singh, Harminder Pal, Kohli, Ravinder Kumar. 2009a. Role of root-mediated interactions in phytotoxic interference of Ageratum conyzoides with rice (Oryza sativa) Flora (Jena). 204 (5): Pages 388-395.
2. Batish, Daizy R., Shalinder Kaur, Harminder Pal Singh & Ravinder Kumar Kohli. 2009b. Nature of interference potential of leaf debris of Ageratum conyzoides, Plant Growth Regul 57: Pages 137-144.
3. Batish, Daizy R., Singh, Harminder Pal, Kohli, Ravinder K., Johar, Vandana, Yadav, Surender. 2004. Management of invasive exotic weeds requires community participation, Weed Technology 18 (Suppl. S): Pages 1445-1448.
4. Bouda, H., L. A. Tapondjou, D. A. Fontem and M. Y. D. Gumedzoe. 2001. Effect of essential oils from leaves of Ageratum conyzoides, Lantana camara and Chromolaena odorata on the mortality of Sitophilus zeamais (Coleoptera, Curculionidae). Journal of Stored Products Research 37 (2): Pages 103-109.
5. Dogra, K. S., R. K. Kohli & S. K. Sood. 2009. An assessment and impact of three invasive species in the Shivalik hills of Himachal Pradesh, India, International Journal of Biodiversity and Conservation 1 (1): Pages 4-10.
8. IUCN/SSC Invasive Species Specialist Group (ISSG)., 2010. A Compilation of Information Sources for Conservation Managers.
Summary: This compilation of information sources can be sorted on keywords for example: Baits & Lures, Non Target Species, Eradication, Monitoring, Risk Assessment, Weeds, Herbicides etc. This compilation is at present in Excel format, this will be web-enabled as a searchable database shortly. This version of the database has been developed by the IUCN SSC ISSG as part of an Overseas Territories Environmental Programme funded project XOT603 in partnership with the Cayman Islands Government - Department of Environment. The compilation is a work under progress, the ISSG will manage, maintain and enhance the database with current and newly published information, reports, journal articles etc.
11. Singh, Harminder P., Daizy R. Batish and Ravinder K. Kohli. 2002. Allelopathic effect of two volatile monoterpenes against bill goat weed (Ageratum conyzoides L.), Crop Protection 21(4): Pages 347-350.
14. Zhao, Jinli, Youxin Ma, Hua Zhu, Hongmei Li, Wenjun Liu, Zengjia Li. 2008. Invasion patterns of seven alien plant species along roadsides in Southern mountainous areas of Yunnan Province, Biodiversity Science 16 (4): Pages 369-380.
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