IAS Toolkit Case study: The Introduction of Parthenium Weed into Ethiopia

Parthenium weed, Parthenium hysterophorus (Asteraceae), is an annual herb with a deep taproot and an erect stem that becomes woody with age. As it matures, the plant develops many branches and may eventually reach a height of two metres. Small creamy white flowers occur on the tips of the numerous stems, each flower containing 4-5 seeds.

Parthenium weed is a native of subtropical areas in South and North America. As an introduced species, it vigorously colonizes weak pastures with sparse ground cover. It will readily colonize arable land, disturbed, bare areas along roadsides and heavily grazed pasture. It is also a health problem as contact with the plant or the pollen can cause serious allergic reactions such as dermatitis and hay fever.

As with most weeds, prevention is much cheaper and easier than cure. P. hysterophorus seeds can spread via water, vehicles, machinery, stock, feral and native animals and in feed and seed. Vehicles and implements, especially earthmoving machinery, passing through parthenium weed infested areas should be washed down with water. The wash down procedure should be confined to only one area, so that any plants that establish from dislodged seed can be destroyed before they set seed. Extreme caution should be taken when moving cattle from infested to clean areas.

Biological control has been implemented in Queensland, Australia, and so far, nine species of insect and a rust pathogen have been introduced to control parthenium weed. The combined effects of biological control agents has reduced the density and vigour of parthenium weed and increased grass production.

Parthenium weed was first reported from Ethiopia at Dire-Dawa, Harerge, eastern Ethiopia in 1988. A second major centre of infestation was subsequently found near Dese, Welo, north-eastern Ethiopia. Both are major food-aid distribution centres, and there is a strong implication that parthenium weed seeds were imported from subtropical North America as a contaminant of grain food aid during the 1980s famine, and distributed with the grain.

By 1999, parthenium weed was widespread in eastern Ethiopia, close to Addis Abeba, and
reported to be spreading into western Ethiopia. The Awash National Park and the Yangudi Rasa National Park are immediately at risk, as the weed spreads in a series of small to large jumps with the accidental human assistance.

As an exotic invasive weed, P. hysterophorus can be expected to continue to expand its range until all suitable habitats are occupied. Efforts to contain it will at best delay this process. Impact on the environment, agriculture and human health will increase, and as the human population becomes sensitised, the medical effects are likely to escalate. Parthenium weed already has a local name, which translates as "no-crop". Since Ethiopia has suffered from famine as much as any country in the world in recent decades, this does not augur well.

Prepared by Matthew Cock, CABI Bioscience Switzerland Centre, 1 Rue des Grillons, CH-2800 Delémont, Switzerland. www.cabi.org/bioscience/switz.htm.
Information on Parthenium edited from Queensland Department of Natural Resources Pest
Facts at http://www.dnr.qld.gov.au/resourcenet/fact_sheets/pdf_files/pp2.pdf. See the Centre for Tropical Pest Management’s Parthenium site
(http://www.ctpm.uq.edu.au/parthenium/parthenium.html) for more information on the weed.

Reference: Wittenberg R. & Cock M.J.W.  Invasive Alien Species: A Toolkit for Best Prevention and Management Practices Invasive Alien Species: A Toolkit for Best Prevention and Management Practices