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Ragweed (Ambrosia artemisiifolia)

Published at: Thursday, 31. January 2008

Ragweeds (Ambrosia artemisiifolia) are a genus of flowering plants from the sunflower family (Asteraceae). Ragweed occurs in the USA and Canada from where it found its way into Europe.

It is most prevalent in Hungary and the surrounding countries, some areas in France, Italy, Switzerland, Austria and Germany. The plant only grows in low altitudes of up to 500 m. It needs long warm summers with high rainfalls and is thus not prevalent in the summer-dry Mediterranean area and in the Alps.

Ragweed proliferates exclusively from seed and is spread by wind and birds but mainly by humans.
Sources for the ambrosia seed are:

• increasing international movement of goods (aircraft, rail, ship)
• international road traffic: cars / trucks / agricultural machines and equipment (wind blasts, tires with cracks, wheel houses, soil attached to shoes, tires, machines etc.)
• transport of soil (trenches and excavation pits, interim storage of soil)
• Import of plants
• Animal feed such as bird seed, chicken feed, exotic bird feed but also winter bird food

Large areas of ragweed growth can be found in untilled soil in development areas, industrial wastelands, earth banks (e.g. building sites), storage areas for building materials, along roads and forest tracks, in fields, flower beds, parks, harbour facilities and oil mills.

A. artemisiifolia blooms from the middle of July to the end of October, with a peak in August and September. As a wind-pollinated plant, ragweed has tremendous seed production (several thousand pollen grains per cubic metre of air). These can cause severe allergic reactions which manifest themselves as allergic rhinitis accompanied by conjunctivitis or even allergic asthma. Ragweed allergies trigger twice as many asthma attacks than other pollen allergies. In some areas in France and Italy infested with ambrosia, up to 12% of the population suffer from ragweed allergies; in North America about 10%-20% of the population are ragweed sufferers. In Australia, Ambrosia artemisiifolia is even called the "asthma plant".

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