Introduction:
Common ragweed (Ambrosia artemisiifolia).
Ambrosia artemisiifolia is a summer annual herbaceous plant that is native to temperate North America in the United States and Canada. Also commonly known as ragweed this forb establishes easily in human impacted and disturbed areas in high abundance. It is considered an invasive species in Europe, parts of Asia and Australia, although it is not an extremely competitively aggressive species and is mainly considered a noxious weed that interferes with other cultivated crops. The main impact of this plant is the copious amount of pollen produced from male flowers that are allergens to sensitive people, compounding health problems like rhinitis, oculorhinitis, asthma and causing skin irritations.
Description:
Ambrosia artemisiifolia is a summer annual herbaceous plant that is erect, with many branches and can reach heights between 1-2 metres with a grooved, reddish, hairy stem. The leaves are opposite, compound, and toothed reaching lengths of 4-10cm long. The tops of the leaves are green and hairy, with white hairs adpressed on the underside of the leaf. Male flowers are green, small, 4-5mm, with bractless flowers arranged in a terminal spike located in the upper portions of the plant, often drooping. The female flowers are located in the axils of the upper leaves, sessile, and inconspicuous in either small clusters or singly. The fruit of the common ragweed is a woody achene, 3-4mm long and 1-2mm wide, with 4-7 spine-like projections, resembling a crown. The leaves are bright green on both sides with whitish nerves. On older plants the lower leaves can be arranged opposite and the upper leaves can be alternately arranged on the stem.
Occurs in:
Agricultural areas, ruderal/disturbed, urban areas.
Common ragweed (Ambrosia artemisiifolia) Distribution in North America shown in green.
Habitat description:
Ambrosia artemisiifolia is commonly found in ruderal or waste sites associated with frequent and extensive disturbance regimes resulting from human activities. Roadsides, railways, gravel pits, construction sites, agricultural fields, waterways, urban areas, and private gardens are all sites that this species establishes easily and prolifically on. Common ragweed is a pioneer species establishing after disturbance in early successional plant communities. It prefers full sun and warm areas, with nutrient rich and slightly acidic soils and can tolerate dry soil conditions. The texture of the soil does not play an important role in establishment but the thickness of the organic layer is inversely related to its presence.
General impacts:
Common ragweed is an abundant seasonal aeroallergen in late-summer to early fall resulting in millions of dollars annually in health care costs and lost labour hours. In studies performed in Europe and North America, approximately 10-15% of the population is sensitive to the pollen of common ragweed causing rhinitis, oculorhinits, asthma, and dermatitis. A. artemisiifolia is also considered a weed pest in agricultural crops like sunflower, sugarbeet, corn and other cereal crops. It also displaces native vegetation in its introduced range especially after a disturbance such as overgrazing or construction which put competitive pressures on the native flora. A. artemisiifolia fruits are a food source for the bobwhite quail but can cause illness in livestock that ingest it.
Close up of the Common ragweed (Ambrosia artemisiifolia).
Geographical range:
Native range: United States, Canada, Mexico.
Known introduced range: Europe, Asia, South America, Guatemala, Cuba, Jamaica, Guadeloupe, Martinique, Maritius, Australia, New Zealand, Hawaii (US).
Management information:
Preventative measures: Preventing an infestation is the most cost-effective approach to weed control. Preventative measures include maintaining healthy vegetation to inhibit the establishment of common ragweed, detection and surveillance along with proper land management to deter an infestation and prevention of overgrazing, sourcing animal feed and hay, along with commercial agricultural seed. Hand-pulling of single plant stands should be combined with early detection and surveillance in areas with beginning infestation. European scientists issued a Call for Action in 2008 to motivate responsible authorities to adopt measures to prevent further spread of ragweed in Europe and to control current infestations.
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