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   Parthenium hysterophorus (herb)  français     
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      Parthenium hysterophorus (Photo: Pankaj Oudhia) - Click for full size   Parthenium hysterophorus (Photo: Pankaj Oudhia) - Click for full size
    Taxonomic name: Parthenium hysterophorus L.
    Synonyms: Parthenium lobatum Buckl.
    Common names: camomille balais (French-Reunion (La Réunion)), camomille z'oiseaux (French-Reunion (La Réunion)), congress grass (English), fausse camomille (French-New Caledonia), herbe blanche (French-Reunion (La Réunion)), Karottenkraut (German), parthenium weed (English), ragweed parthenium (English), Santa Maria feverfew (English), whitetop weed (English)
    Organism type: herb
    Parthenium hysterophorus is an annual herb that aggressively colonises disturbed sites. Native to Mexico, Central and South America, Parthenium hysterophorus was accidentally introduced into several countries including Australia, India, Taiwan and Ethiopia. In some areas it has become an extremely serious agricultural and rangeland weed. Parthenium hysterophorus is also known to be allergenic to some people and consumption by livestock can taint meat.
    An erect ephemeral herb known for its vigorous growth. It is light green with branching stems, finely lobed leaves and grows up to 1.5 metres, occasionally reaching 2m in deep rich soils. Young plants form a basal rosette of strongly dissected leaves that are up to 30cm in length. Once stem elongation is initiated, smaller leaves are produced and the plant becomes much-branched in its extremities.
    Occurs in:
    agricultural areas, range/grasslands, ruderal/disturbed, scrub/shrublands, urban areas
    General impacts
    Infestations of parthenium weed can degrade natural ecosystems. The plant can produce serious allergenic reactions in humans. Parthenium aggressively colonises disturbed sites and has major impacts on pasture and cropping industries, spreading to and impacting on new areas.
    Outcompetes native species, in part due to allelopathy.
    Geographical range
    Native range: Native to Mexico, Central and South America.
    Known introduced range: An aggressive invader of agricultural and rangeland habitats in Australia, India, Taiwan and Ethiopia. Also present in Papua New Guinea, Madagascar, South Africa, Caribbean region and Florida USA.
    Introduction pathways to new locations
    Agriculture: Thought to have been introduced into Ethiopia and India with contaminated cereal grain, and into Australia in contaminated pasture seed from the USA.

    Local dispersal methods
    On animals:
    Other (local): Transport of hay and grain.
    Road vehicles:
    Translocation of machinery/equipment (local):
    Water currents:
    Management information
    Control of parthenium weed can be managed using a combination of methods depending on the site, including biological control agents, pasture management, cultivation and chemicals.

    Preventative measures: Emphasis must be laid on establishing detection/monitoring procedures and stopping the spread of parthenium weed via vehicles and as a contaminant. A Risk assessment of Parthenium hysterophorus 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 18 and a recommendation of: reject the plant for import (Australia) or species likely to be a pest (Pacific).

    The Parthenium weed management book provides information on management and control aspects including spread minimization, pasture management, herbicide use, biological control and health aspects. It also describes the parthenium weed and provides basic information about its ecology and biology, reproduction and spread, current distribution, and potential threat. The Weed Control Methods Handbook provides you with detailed information about the tools and techniques available for controlling invasive plants, or weeds, in natural areas. This Handbook is divided into eight chapters, covering a range of different control methods: manual, mechanical, promoting competition from native plants, grazing, biocontrol, herbicides, prescribed fire, solarization, flooding, and other, more novel, techniques. Each control method has advantages and disadvantages in terms of its effects against the target weed(s), impacts to untargeted plants and animals, risks to human health and safety, and costs.

    Biological: Biological control using insects and fungi is being pursued in Australia and in India.

    Sexual reproduction.
    Highly prolific. An average plant can produce 15,000 seeds and large plants are known to produce 100,000 seeds.
    Lifecycle stages
    Germination temperatures for Parthenium occur across the 8 to 30° C range with the optimum germination temperature being 22 to 25° C. Persistence tests demonstrated that more than 70% of parthenium seeds buried at 5cm below the soil surface survived for at least 2 years whereas surface-lying seeds survived for no longer than 6 months. Parthenium weed seeds were found to be very persistent in the soil and there was relatively little change in their abundance over an 18 month period. The germination rate of parthenium weed seeds was also significantly faster than that of all other species present (Sheldon Navie, 2003).
    Reviewed by: Dr. Rachael MacFadyen, Queensland Department of Natural Resources, Australia. William Overholt, International Centre of Insect Physiology and Ecology, Nairobi, Kenya.
    Compiled by: IUCN SSC Invasive Species Specialist Group
    Updates with support from the Overseas Territories Environmental Programme (OTEP) project XOT603, a joint project with the Cayman Islands Government - Department of Environment
    Last Modified: Monday, 4 October 2010

ISSG Landcare Research NBII IUCN University of Auckland