Fireweed (Senecio madagascariensis Poiret, also called Madagascar ragwort) is one of more than 1200 species of Senecio distributed throughout the world. It is a native of Madagascar and South Africa that became established in Hawai‘i in the early 1980s.In some parts of those islands, up to 60 percent of the vegetative cover is fireweed. In such areas, forage production is estimated to be reduced by 30–40 percent. Of the more than 1200 different species of Senecio, only 25 are proven to be toxic to animals. Although evidence is limited, it is strongly suspected that S. madagascariensis may also be toxic to animals. The principal toxins in these species are compounds known as pyrrolizidine alkaloids (PAs). PA concentrations vary with the species and their growth stages. This article discusses the amounts of PAs found in fireweed in Hawaii, potential effects and signs of poisoning in livestock and using adaptive management for developing an integrated weed management program.
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