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Alternanthera philoxeroides (aquatic plant, herb) |
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Management Information
Preventative measures:: The Australian Department of the Environment and Heritage (2003) state that, "Alternanthera philoxeroides has rarely, if ever, been successfully eradicated once it has infested a water body, despite numerous costly attempts. For this reason, the highest priority for the management of alligator weed is an effective system of early detection and eradication before infestations become established."
A Risk assessment of Alternanthera philoxeroides for Australia was prepared by Pacific Island Ecosystems at Risk (PIER) using the Australian risk assessment system (Pheloung, 1995). The result is a score of 12 and a recommendation of: reject the plant for import (Australia) or species likely to be of high risk (Pacific).
Mechanical: Coventry et al. (2002) report on the use of a weed harvester, which was used to remove 120 tons of alligator weed. The authors state that, "A further 18kgs of fragments broken of by the machine were removed by hand using small boats. This is an effective way of removing biomass from accessible areas but other methods are required to deal with re-growth and inaccessible areas." Caution must be taken to ensure that all fragments are collected. Mechanical harvesting can exacerbate the invasive potential of the species of all fragments are not gathered.
Chemical: Gunasekera and Bonila (2001) tested four chemicals, Dichlobenil, Glyphosate, Metsulfuron methyl and Metsulfuron methyl with Glyphosate on A. hiloxeroides. The authors found that each chemical provides its own measure of control against A. philoxeroides. Coventry et al. (2002) offer an in-depth review of 12 combinations of different herbicidal treatments that have been studied. Please refer to Coventry et al. 2002 in the section labeled Herbicides
Biological: Gagne et al. (2004) have found a new species of cecidomyiid, Clinodiplosis alternantherae that is injurious to A. philoxeroides. C. alternantherae forms galls on branch tips and is a likely candidate to aid in the control of the invasive, alien A. philoxeroides. Barreto and Torres (1999) identified two fungal species, Nimbya alternantherae and Cercospora alternantherae which have pathogenic effects on A. philoxeroides. The authors conlcude that, "N. alternantherae was shown to be very damaging and appears to have biocontrol potential."
Buckingham (1996) states that from 1964 to 1971 three South American species were released in North America for biological control of A. philoxeroides. The author states that, "The flea beetle Agasicles hygophila strips the leaves from the stems and the moth Vogtia malloi bores inside the stems. Heavy damage by either species kills the stems thereby causing the mat to break up, clearing the waterway. The thrip Amynothrips andersoni feeds on the young apical leaves. Heavily damaged plants are often stunted." Coventry et al. (2002) recommend two insects for introduction to Australia for biological control of A. philoxeroides; the thrips Amynothrips andersoni, and the flea beetle Disonycha argentinensis.
Tan et al. (2002) have identified a disease caused by Fusarium sp that occurs occaisonally on natural populations of A. philoxeroides. Mass production of the fungal inoculum should be possible, but a system for mass production needs to be tested and established. The fungus controlled A. philoxeroides effectively under laboratory and greenhouse conditions, as well as in the field. Therefore, it is considered a good biocontrol agent candidate for managing A. philoxeroides in some terrestrial and aquatic crops."
Location Specific Management InformationAustralia
"In Australia approximately $3 million has been spent to successfully control a small infestation in an irrigated system in order to prevent losses estimated at $250 million. The weed has threatened turf and vegetable production in the Lower Hunter and Sydney basin. In most cases control programs have not prevented expansion of the larger infestations nor protected areas previously free of the weed. An efficient and effective management program must be implemented otherwise alligator weed will invade all major catchments, degrade conservation areas and increase costs of waterway management.
The Weeds of National Significance Strategic Plan aims to coordinate the management of alligator weed, prevent its further spread and protect high-risk sites. Community education is a key factor for its success. Non-core infestations are a priority and are targeted for eradication. Core infestations are targeted for containment and reduction of spread. Further investigations into improving integrated control techniques are required. The National Alligator Weed Working Group, consisting of stakeholders from states and industries, will coordinate this management.
Chemical Control: Chemical eradication of small infestations is currently being attempted in many backyards throughout Australia. It has been suggested that until new compounds are available little progress will be made with herbicidal control.
Biological control: The flea beetle Agasicles hygrophila provides good control in aquatic environments in the Sydney region. This is a truly aquatic insect and is limited to warm temperate and sub tropical areas. The predicted range for alligator weed in Australia far exceeds the predicted range for the flea beetle. A moth Arcola malloi contributes to control in aquatic habitats and is established but has no impact on terrestrial alligator weed. Further biological control programs are being targeted.
Physical control: The value of physical controls (mechanical or manual) is limited to small and isolated situations and could be particularly useful in removing initial invaders of a catchment if they can be located early enough. Mechanical removal, particularly in waterways, is problematic and may contribute to downstream spread. Disposal of the collected material poses specific problems." Barren Box Swamp (Australia)
The Barren Box swamp infestation near Griffith, NSW, has been very significantly reduced but not eradicated as a result of intensive work over a number of years costing several million dollars (Coventry et al. 2002). Botany Wetlands (Australia)
The nationally important wetlands, Botany Wetlands are ecologically as well as aesthetically significant. They supplied drinking water for Sydney in the mid 1800s. Alligator weed was first reported in the waterways around 1985. Until the mid 1990s the infestation was only occasionally treated with herbicides, by which time the infestation was out of control and posed a significant threat to the wetlands.
Sydney Water (which provides drinking water and wastewater services to over four million people in the Sydney, Blue Mountains and Illawarra areas, including the Botany Wetlands which are situated within the metropolitan area of Sydney) introduced an integrated weed management approach to deal with alligator weed infestation. This approach involves close and regular monitoring for new infestations, herbicide treatment for both terrestrial and aquatic infestations and manual removal of floating masses. Other strategies in the integrated approach include controlled burning of sedges and rushes, large scale planting of native water plants in treated areas and lowering of water levels to allow better control. Also, to minimise environmental damage from chemicals, herbicides are not applied when the biological control agents are most active.About 90-95% of the previous alligator weed infestation has been controlled and removed since the adoption of the new integrated management plan in 1997, the weed however has not been completely eradicated. For more details please see Case study: Integrated management of alligator weed in Botany Wetlands in Sydney . (DEH, 2003) China
A host-specific flea beetle, Agasicles hygrophila, introduced from the USA in 1986 as a biological control agent, has become widely established in South China and has effectively controlled the weed in many water bodies. It has been observed, however, that the beetle's ability in controlling the weed in terrestrial habitats has been limited, apparently due to its poor and/or greatly varying pupation rates (Rui-Yan and Ren, 2004). Hunter Estuary Wetlands (Australia)
A management plan for the Nature Reserve is currently being implemented (2002), addressing numerous conservation and management initiatives to preserve and enhance the area for nature conservation. Management policies and practices are outlined for geology and soils, hydrology, water quality and catchment management, native and introduced flora and fauna, wetland rehabilitation, cultural heritage, fire management and use and promotion of Kooragang Nature Reserve. Specific conservation measures include pampas grass control, vegetation mapping, alligator weed control, rehabilitation as well as artificial construction of migratory shorebird habitat and shorebird monitoring. Lower Hunter River (Australia)
Alligator weed currently infests 2,500 hectares of terrestrial and 500 hectares of aquatic area in the Lower Hunter region (Commonwealth of Australia, 2000). “Alligator weed has eliminated small crop and turf farming from parts of the Lower Hunter” (Commonwealth of Australia, 2000). New Zealand
A. philoxeroides is included in the First Schedule of the National Pest Plant Accord. All plants on the list are designated as Unwanted Organisms, and are banned from sale, propagation and distribution throughout New
Zealand. Please see National Pest Plant Accord for the complete list.
Chemical, mechanical and biological control of alligator weed all have limitations. Herbicides often only destroy the foliage, but fail to kill the roots, from which it rapidly resprouts. Physical removal is only recommended for small infestations where all of the plant can be removed, as breakup of plant may cause new infestations to establish. Inappropriate disposal of alligator weed may also lead to new infestations. In New Zealand, the most successful biocontrol agent, the leaf feeding Chrysomelid flea beetle (Agasicles hygrophila), does quite well on lakes, but is not able to establish in terrestrial environments. It also has a more restricted potential distribution in New Zealand than alligator weed (Bassett, I., pers. comm. July 2005).
Stewart et al. (2000) studied the effects of A. hygrophila, a biological control agent for A. philoxeroides and determined that A. hygrophila is unlikely to cause a reduction in alligator weed in New Zealand even in conjunction with Arcola malloi. United States (USA)
A host-specific flea beetle, Agasicles hygrophila, introduced from the USA in 1986 as a biological control agent, has become widely established in South China and has effectively controlled the weed in many water bodies. It has been observed, however, that the beetle's ability in controlling the weed in terrestrial habitats has been limited, apparently due to its poor and/or greatly varying pupation rates (Rui-Yan and Ren, 2004).
The University of Florida (UNDATED) states that, "There were 97,000 problem acres of A. philoxeroides in the US in 1963; by 1981 there were less than 1,000 problem acres." The authors state that this level of control was achieved through the use of three separate biological control agents. The first biocontrol insect released against A. philoxeroides was the alligatorweed flea beetle (Agasicles hygrophila). The authors state that, "The second biocontrol insect released to combat A. philoxeroides was the alligatorweed thrips (Amynothrips andersoni)." The third control organism that was released was the alligatorweed stem borer (Vogtia malloi) (University of Florida, UNDATED).
For a detailed history of biological control efforts in the eastern United States, please follow this link G. R. Buckingham In: Van Driesche, R., et al., 2002, Biological Control of Invasive Plants in the Eastern United States, USDA Forest Service Publication FHTET-2002-04, 413 p. Waikato Region (New Zealand)
A. philoxeroides is classified as an “Eradication Plant Pest” by Environment Waikato. Environment Waikato will directly manage and control it, as well as monitor the weed and providing identification and control information to the community.
Please see definitions for hierarchy of pest designations.
Management Resources/Links
3. Barret, R. W., and A. N. L. Torres. 1999. Nimbya alternantherae and Cercospora alternantherae: Two new records of fungal pathogens on Alternanthera philoxeroides (alligatorweed) in Brazil. Australasian Plant Pathology. 28(2). 1999. 103-107. 4. Bassett, I., pers. comm. July 2005. Alligator weed: Potential invader of forest catchments? Effects of shade on alligator weed growth. Centre for Biodiversity and Biosecurity Seminar Series, University of Auckland. 5. Buckingham, G. R. 1996. Biological control of alligatorweed, Alternanthera philoxeroides, the world's first aquatic weed success story. Castanea. 61(3). 1996. 232-243. 8. Champion, P.D.; Clayton, J.S. 2001. Border control for potential aquatic weeds. Stage 2. Weed risk assessment. Science for Conservation 185. 30 p.
Summary: This report is the second stage in the development of a Border Control Programme for aquatic plants that have the potential to become ecological weeds in New Zealand. Importers and traders in aquatic plants were surveyed to identify the plant species known or likely to be present in New Zealand. The Aquatic Plant Weed Risk Assessment Model was used to help assess the level of risk posed by these species. The report presents evidence of the various entry pathways and considers the impact that new invasive aquatic weed species may have on vulnerable native aquatic species and communities.
Available from: http://www.doc.govt.nz/upload/documents/science-and-technical/SFC185.pdf [Accessed 13 June 2007] 9. Commonwealth of Australia. 2000. ALLIGATOR WEED (Alternanthera philoxeroides) Strategic Plan. Commonwealth of Australia and the National Weeds Strategy Executive Committee. 10. Coventry, R., M. Julien, and J. Wilson. 2002. Report of the 1st CRC for Australian Weed Management Alligator Weed Research Workshop. Department of Land & Water Conservation, Windsor, NSW. 11. Environment Waikato. 2002. Alligator weed (Alternanthera philoxeroides). 15. Flanagan, G.J. 1999. Agnote Alligator weed 16. Gagne, R. J., A. Sosa, and H. Cordo. 2004. A new neotropical species of Clinodiplosis (Diptera: Cecidomyiidae) injurious to alligatorweed, Alternanthera philoxeroides (Amaranthaceae). Proceedings of the Entomological Society of Washington. 106 (2). April 2004. 305-311. 17. Gunasekera, L. 1999. Alligator weed - An aquatic weed present in Australian backyards. Plant Protection Quarterly. 14 (2). 1999. 77-78. 18. Gunasekera, L., and J. Bonila. 2001. Alligator weed: Tasty vegetable in Australian backyards? Journal of Aquatic Plant Management. 39 January, 2001. 17-20. 20. Julien, M. H., B. Skarratt, and G. E. Maywald. 1995. Potential Geographical Distribution of Alligator Weed and its Biological Control by Agasicles hygrophila. Journal of Aquatic Plant Management 33: 55-60. 21. Napompeth, B. UNDATED. Biological Control of Paddy and Aquatic Weeds in Thailand. National Biological Control Research Center (NBCRC), Kasetsart Univseristy. 22. National Pest Plant Accord, 2001. Biosecurity New Zealand.
Summary: The National Pest Plant Accord is a cooperative agreement between regional councils and government departments with biosecurity responsibilities. Under the accord, regional councils will undertake surveillance to prevent the commercial sale and/or distribution of an agreed list of pest plants.
Available from: http://www.biosecurity.govt.nz/pests-diseases/plants/accord.htm [Accessed 11 August 2005] 23. Ramsar Sites Information Service, 2005. Ramsar Sites Database
Summary: The Ramsar Sites Information Service provides information on wetlands designated as internationally important under the Convention on Wetlands (Ramsar, 1971). These wetlands are commonly known as Ramsar Sites. Wetlands International manages and develops the Ramsar Sites Database (RSDB) under contract to the Ramsar Convention Secretariat. This core Ramsar Sites Database is a searchable database, fully accessible through the internet with a password protected data entry system, and an unprotected reporting system for public use.
Available from: http://www.wetlands.org/RSDB/default.htm [Accessed 25 April 2005] 25. Roy, B., Popay, I., Champion, P., Trevor, J., and Rahman, A., 2004. An Illustrated Guide to Common Weeds of New Zealand 2nd Edition New Zealand Plant Protection Society 27. Rui-Yan, M., and W. Ren. 2004. Effect of morphological and physiological variations in the ecotypes of alligatorweed, Alternanthera philoxeroides on the pupation rate of its biocontrol agent Agasicles hygrophila Zhiwu Shengtai Xuebao. 28 (1). Jan. 2004. 24-30. 28. Sainty, G., G. McCorkelle, and M. Julien. 1998. Control and spread of Alligator Weed Alternanthera philoxeroides (Mart.) Griseb., in Australia: lessons for other regions. Wetlands Ecology and Management 5: 195-201, 1998. 29. Sheng, Q., S. Jun-Ming, Z. Cheng-Qun, S. Geng-Yun, H. Jin-Liang, and W. Feng-Liang. 2003. The influence of cropping systems on weed communities in the cotton fields of Jiangsu Province. Zhiwu Shengtai Xuebao. 27 (2). Mar. 2003. 278-282. 30. Tan, W. Z., Q. J. Li, and L. Qing. 2002. Biological control of alligatorweed (Alternanthera philoxeroides) with a Fusarium sp. BioControl 47: 463-479, 2002. Results Page: 1
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