ragweeds

Ragweeds are flowering plants in the genus Ambrosia within the daisy family (Asteraceae). They include several species native to North America, most notably common ragweed (Ambrosia artemisiifolia) and giant ragweed (Ambrosia trifida). Today they occur in many temperate regions around the world, where they colonize disturbed soils, fields, roadsides, and waste places.

Ragweeds are annual herbs with variable height, often reaching up to 1 meter or more. They have finely divided leaves and produce small, inconspicuous flowers arranged in dense inflorescences. Pollen is produced in large quantities by the flowers, and in many species it is released during late summer and autumn. The pollen is light and wind-dispersed, allowing it to travel long distances. Seeds develop from female flowers and can persist in the soil seed bank for several years, aiding their spread and persistence.

Ragweeds are widely recognized for their allergenic potential. Ragweed pollen is a major trigger of allergic rhinitis and can contribute to asthma in sensitive individuals. The pollen’s windborne nature means it can affect people far from the plants themselves, and shifts in climate and land use have facilitated their spread in non-native regions.

Management focuses on reducing seed production and limiting spread. Practices include mowing or cutting before flowering, cultivation to disrupt seed banks, and the use of herbicides in agricultural or urban settings. In newly invaded areas, early detection and removal of flowering plants are important to limit establishment.