Senecio jacobaea L.

Tansy ragwort

BACKGROUND

Tansy ragwort is a Eurasian weed first reported in Oregon in 1922. It spreads primarily by seed. A single tansy ragwort plant may produce up to 150,000 seeds, which may remain viable for up to 15 years. All parts of this weed are poisonous to cattle and horses, while sheep are affected to a lesser extent. Like other groundsels, it has several alkaloids which produce irreversible liver damage. Flowering occurs from July to September. While tansy ragwort is not presently in all the western states, it does infest millions of acres of private and public range and pasture land in the Pacific Northwest.

DESCRIPTION

Tansy ragwort is a biennial or short-lived perennial. Seeds germinate the first year and form a rosette of raggedly lobed leaves up to nine inches long. Flower stalks develop the second year, growing up to six feet tall, with many branches near the top. Stem leaves are two to three times pinnate with blunt tips and blades that attach directly to the stalk. Numerous yellow, one inch wide, daisy-like flower heads with golden or light brown centers form at the tip of each branch from midsummer to fall. Each flower head has 10 to 13 flowers. Seeds are tiny and are tipped by hairlike plumes that carry seeds in the wind for long distances. In the first year of growth the plant will have a cobwebby pubescence.

DISTRIBUTION

This weed is widespread on the coast and Cascade mountains of Washington, Oregon and California. More recently is has shown up in Idaho and Montana. Montana has suffered huge infestations in large areas burned during the 1996 fire season. On the Clearwater National Forest, it has shown up at one location on the Palouse Ranger District. District personnel have been successful so far pulling the few weeds by hand.

CONTROL

Biological control agents provide fair to excellent control west of the Cascades, but have not been tested in Idaho. These include a seed head fly, a root/defoliating flea beetle, and a defoliating moth. Herbicides are available. It should be noted that damage prior to the plant maturing may delay death and cause regrowth the following year.