Ageratina riparia is unpalatable to livestock and is toxic. It reduces the carrying capacity of pastures and rangeland and restricts movement of machinery and stock. The weed has potential for rapid natural spread throughout its potential...
Ageratina riparia is unpalatable to livestock and is toxic. It reduces the carrying capacity of pastures and rangeland and restricts movement of machinery and stock. The weed has potential for rapid natural spread throughout its potential range (e.g., high reproductive potential and highly mobile propagules). A. riparia is a prolific seeder and grows very fast, becoming the dominant vegetation in an invaded area (Barreto and Evans, 1988). Leachates from leaves and plant litter have an allelopathic effect on other plants. A. riparia is among the primary threats to 25 endangered species on the island of Oahu in Hawaii. The potential negative impacts outweigh any limited value the species has as an ornamental.
A. riparia was added to the US Federal Noxious Weed List and seed list in 2010. Hawaii lists A. riparia as a noxious weed for eradication and control purposes.
A. riparia can be an erect or sprawling herb to small shrub. Stems are cylindrical and have a purplish tint. Its green, opposite leaves can grow up to 15 centimeters long and 4 centimeters wide and range from lanceolate to narrow ovate. Leaves also display toothed margins. Flowers are arranged in flat-topped showy white clusters that produce 5-angled seeds 1-2 millimeters long and topped with 3-4 millimeter long bristles.
A. riparia is a serious pest in Africa, India, Indonesia, Papua New Guinea, Southeast Asia, Australia, New Zealand, Jamaica, Madagascar, and Hawaii. It was introduced to the USA as an ornamental and by agricultural contamination. It is likely to establish populations in the warm southeast USA, particularly in Florida and Texas. Its preferred habitats include misty upland pastures and mountainous areas with high levels of precipitation.
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
A. riparia is a prolific seeder and grows very fast, becoming the dominant vegetation in an invaded area (Barreto & Evans, 1988). In Australia, mature plants produce between 10,000 and 100,000 seeds annually. The seed can germinate immediately when in light (Parsons and Cuthbertson, 1992). Seeds are dispersed by wind and water. Colonies increase in density and size by horizontal spread and rooting at nodes.
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
A pest risk assessment completed by APHIS, USA (Lehtonen, 2001) ranked A. riparia as medium in consequences of introduction and high in likelihood of introduction, resulting in an overall ranking of medium/high risk potential and the species was added to the US Federal Noxious Weed List and seed list in 2010. Hawaii lists A. riparia as a noxious weed for eradication and control purposes, which authorizes the State department of Agriculture to conduct control activities for this weed as time and resources permit.
A. riparia is resistant to many herbicides, but can be controlled if treated repeatedly (Parsons and Cuthbertson, 1992). The most effective method of biological control of this weed was the introduction of the fungus, Entyloma ageratinae, to infested areas in the state of Hawaii.
Barreto, Robert W. and Evans, Harry C. 1988. Taxonomy of a Fungus Introduced into Hawaii for Biological Control of Ageratina riparia (Eupatorieae; Compositae), with Observations on Related Weed Pathogens. Transactions of the British Mycological Society 91: 81-97.
Lehtonen, Polly. 2001. Weed Risk Assessment for Ageratina riparia (Regel) R. M. King and H. Robinson (Mistflower) Version 6 Revised February 22, 2009 by Shirley Wager-Pagé Addendum to a report, Analysis and Assessment of the Invasive risk of Ageratina riparia, submitted by Sarah Reichard and Lizbeth Seebacher, University of Washington, College of Forest Resources, Center for Urban Horticulture. http://www.aphis.usda.gov/plant_health/plant_pest_info/weeds/riskassessments.shtml
Parsons, W. T. & E. G. Cuthbertson. 1992. Noxious weeds of Australia. Inkata Press, Melbourne, Sydney.