Ecology Distribution Management Info Impact Info References and Links Contacts

General Impact Gunasekera (1999) states that, "Alternanthera philoxeroides is considered to be one of the worst aquatic weeds in the world. The aquatic form of the plant has the potential to become a serious threat to waterways, agriculture and the environment. The terrestrial form grows into a dense mat with a massive underground rhizomatous root system. The canopy can smother most other herbaceous plant species." Buckingham (1996) states that, "Floating stems grow across the surface of the waterway forming a dense interwoven mat. This mat clogs the waterway and out competes native plants along the shore." The Commonwealth of Australia (2000) states that, "Alligator weed disrupts the aquatic environments by blanketing the surface of the water impeding penetration of light, gaseous exchange (sometimes leading to anaerobic conditions) with adverse affects on flora and fauna. Mats impede flow and lodge against structures thereby promoting sedimentation and contributing to flooding. They prevent access to and use of water, promote health problems by providing habitats for mosquitoes and degrade natural aesthetics." Control of this species has proven to be an expensive and complicated ordeal wherever it has established.          Location Specific Impacts: Australia   Economic/Livelihoods: In Australia, alligator weed may invade important agricultural systems such as irrigation areas and significantly reduce production. In New Zealand and Australia it also has the potential to cause photosynthesisation of the skin in cattle, resulting in cancerous lesions. When the Barren Box Swamp (NSW) infestation was found in 1994, it was estimated that the potential costs to the irrigation farming community could be as high as $250 million per year. An annual control programme would have cost $6 to $8 per mega L of water at the farm gate, an increase of 30% delivery cost. Hence an eradication programme of this relatively small infestation was undertaken, costing more than $3 million to date and continuing. In the Hawkesbury/Nepean catchment the weed threatens the $35 million per year turf industry and the $50 million per year vegetable industry, as well as recreational use and in-stream extraction. Ecosystem change: In Australia, alligator weed disrupts natural aquatic ecosystems by blanketing the surface of the water with thick mats and impeding penetration of light to the ground. Mats promote sedimentation and flooding and prevent gaseous exchange (which may lead to anaerobic conditions). Flow-down affects of these significant ecosystem changes (on native flora and fauna) are certain. Human nuisance: Alligator weed may prevent access to water bodies in Australia, thereby disrupting various recreational activities as well as potentially threatening livelihoods and industries dependent on clear waterways. For example, Liverpool City Council spent $8,000 annually to reduce the visual impact of alligator weed and to maintain a section of the river available for use by a rowing club. Alligator weed may cause health problems in Australia by providing habitats for mosquitoes. Hunter Valley (Australia)   Economic/Livelihoods: Currently $120,000 per year is spent by Hunter Valley councils to try and contain the weed (Coventry et al. 2002). Liverpool (Australia) (Australia)   Economic/Livelihoods: Liverpool City Council spent $8,000 annually to reduce the visual impact from a bridge and to maintain a section of river available for use by a rowing club (Commonwealth of Australia, 2000). New Zealand   Agricultural: Alternanthera philoxeroides is a pasture and horticulture weed. Stock sometimes suffer from a skin complaint, with increased sensitivity to sunlight, after contact with Alternanthera philoxeroides. It blocks drains and increases flood damage. Its ecological impacts are not well known (Bassett, I., pers. comm. July 2005). Human nuisance: Alternanthera philoxeroides negatively affects recreational water use (Bassett, I., pers. comm. July 2005).