A biennial weed or short-lived perennial, the ragwort (Senecio jacobaea), has become a serious noxious weed in many locations. The plant has vigorous growth and reproduction habits to easily out-compete native plants. Highly toxic, the weed poisons cattle and horses when consumed. The animals' milk production also become affected by the toxins. Honey produced from the pollen of the ragwort contains poisonous alkaloids.
In the early 1900s, ragwort began to be seen in seaports, according to King County (Wash.) Noxious Weeds. Native to Europe, the plants began to spread throughout the United States. Hay was a common source of spread. In 1922, the weed began to be reported in Oregon. Seed germination begins in the fall or early winter.
The ragwort plant spreads through its root system or seeds. Each plant has the capability of producing 4,700 to around 174,000 seeds, according to the Alaska National Heritage Program and the University of Alaska. After dispersal the seeds remain viable for up to 15 years. The wind actively disperses the seeds upon maturity.
In the first years of the ragwort's life, it produces only foliage in a rosette form. The plant also put energy into growing its root system. The foliage appears a deep green on the top side with a lighter greenish-white shade on the bottom side of the leaves. Each leaf has a ruffled appearance and measures approximately nine inches in length.
In the second year of the plant's life, it produces flowers stalks that tower six feet in height. Each flower cluster is composed of numerous tiny, yellow blossoms. Each blossom contains 13 petals. Flowering runs from July to September.
Seeds follow flowering. Each tiny seed is tipped by tiny plumes of hairlike threads that give the seeds the ability to fly easily on the wind. The seeds often fly nine miles from the parent plant. They also have the ability to live through birds' and mammals' digestive tracts and emerge viable.