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Parthenium hysterophorus

Parthenium hysterophorus

Recognize the problem

Family: Asteraceae (daisy family).

Common names: Parthenium weed, false ragweed, fever weed,  carrot weed, carrot grass, congress weed, famine weed, white top.

Amharic: Faramsisa, qinche arem, kalignole; French: Parthenium matricaire, Parthène multifide.

Annual erect broadleaved herb, 0.5-1.5 m high; stem branched with alternate leaves, longitudinally grooved and covered in short hairs; young plants form a basal rosette of leaves.

Leaves: Pale green and covered with short stiff hairs; rosette and lower stem leaves deeply divided and large (3-30 cm long and 2-12 cm wide); upper stem leaves are shorter and less divided.

Flowers: White small compact heads (about 5 mm across), clustered at the tips of branches, each flowerhead has 5 distinctive "petals".

Fruits: Small (1.5–2.5 mm long), each containing one seed; five in each flowerhead.

Seeds: Black, two thin white scales, 2 mm long; 10-25,000 per single plant with no dormancy period; potential to build up persistent seed bank.

Roots: Deep tap root.

Background

Origin: Latin America.

Introduction: As medicine, ornament and accidentally as a contaminant.

Habitat: Semi-arid, tropical, subtropical or warm temperate regions; favouring heavier fertile soils, but able to grow on a variety of soil types from sea level up to 2400m; particularly prolific in disturbed habitats.

Spread: By seeds with wind, water, animals, machinery, vehicles and as contaminant of crop and pasture seed and fodder.

Invades: Crops, plantations, pasture, banks of watercourses such as drainage ditches and streams, gardens and degraded and disturbed land.

Impacts: Parthenium weed inhibits the germination and growth of other plants, thereby reducing crop yields and displacing palatable species in natural and improved pastures. Parthenium weed may cause severe crop yield losses (>50%). Parthenium weed is also a secondary host for a range of crop pests. Livestock carrying capacity may be reduced by as much as 90%. The plant also poses serious health hazards to livestock, and can cause severe allergenic reactions in the form of skin rashes and breathing problems in people who regularly come into contact with the weed.

Declared a noxious weed in Kenya in 2010 (Suppression of Noxious Weeds Act: CAP 325). The Minister of Agriculture can compel land owners to remove it  from their land or have it otherwise removed.

The recommendations in this factsheet are relevant to: All Countries

Authors: CABI. Edited by participants from Kenya, Tanzania, Ethiopia, Malawi and Rwanda at a workshop in Nairobi, February 2016
CABI
tel: +254 (0)20 2271000 email: africa@cabi.org

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