Tansy Ragwort (Senecio jacobaea)
Tansy ragwort (Senecio jacobaea) is a Eurasian weed first reported in Oregon in 1922. It is now widespread on the coast and Cascade Mountains of Oregon and Washington. Regenerated primarily by seed, a single tansy ragwort plant may produce up to 150,000 seeds which remain viable for up to 15 years. All parts of this weed are poisonous, and it can cause liver damage to cattle and horses, and is lethal in very large doses. Sheep are affected to a lesser extent. Most tansy poisoning occurs when the rosettes are below the level of the surrounding grass making it harder for grazing animals to differentiate.
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. Numerous yellow, 1-inch wide, daisy-like flower heads with golden or light brown centers from the tip of each branch from midsummer to fall. Seeds are tiny and are tipped by hair-like plumes that carry seeds in the wind for long distances.
Management techniques
Biological control agents have proven to be the most effective means of controlling tansy ragwort, especially in areas of large infestations. The ragwort flea beetle (Longitarsus jacobaeae) has been very successful. The flea beetle larvae mine the roots of tansy rosettes. Adult flea beetles feed on the leaves causing a typical shot-holed appearance.
The cinnabar moth (Tyria jacobaeae) is another, more familiar, bio-control agent used for tansy ragwort. The orange and black striped cinnabar moth larvae strip the foliage and destroy the flowers often leaving a bare stock. The cinnabar moth, in conjunction with the ragwort flea beetle, has proven very effective in controlling tansy ragwort in northern California, Oregon, and Washington west of the Cascades. Both the ragwort flea beetle and the cinnabar moth do best on sunny slopes where flooding does not occur. Sheep are helpful in preconditioning pastures.
Like most biological control agents, populations of ragwort flea beetles and cinnabar moths are constantly fluctuating depending upon availability of tansy ragwort and weather conditions. Generally, the insects’ population will peak and then die back because they’ve literally eaten themselves out of house and home. It will take a couple of years for the host to make a come back. Within a few years lag time the biological agents will rebuild their own population enough to control the host weed again.
Other management techniques include pulling, cutting, and sheep grazing. Tansy ragwort most commonly infests areas that have been disturbed or poorly managed.
