Common Name: stinking willie Scientific Name: Senecio jacobaea Code: SEJA Group: Dicot Family: Asteraceae Growth Habit: Forb/herb Duration: Perennial

What does it look like?

This perennial, in the dandelion family, generally grows to three and one-third feet tall but sometimes reaches a height of ten feet. Numerous daisy-like yellow flowerheads, often an inch-wide, have golden or light brown centers and form at the tip of each branch. The dark-green, stalkless leaves are deeply and pinnately dissected into irregular segments giving the plant a ragged appearance. Ray flowers distinguish this plant from the common tansy (Bossard et al.2000). This plant blooms from July through September.

One ragwort plant can produce 4,700 to 174,000 seeds that remain viable in the soil for several years. These seeds are dispersed primarily by wind but can also be carried by animals. As well as seed reproduction, tansy ragwort can regenerate from root fragments left behind in soils and vehicles (Bossard et al. 2000).

Where does it grow?

Native to Western Europe, and western Asia, tansy ragwort migrated to Argentina, New Zealand, Australia, Canada, and the Western United States. Ragwort is common in pastures, roadsides, forested and clearcut lands, and other disturbed places. It prefers light, well-drained soils but can become established in heavier disturbed soils, where trampling or cultivation occurs.

Is it in our watershed?

Tansy ragwort was not identified on surveys conducted by MRC in 2004 and is not currently documented in the Mattole.

What problems does it cause?

As with many invasive species, ragwort outcompetes native and naturalized species of grasses and forbs, often establishing heavy, widespread infestations in various ecosystems. It has been known to cause major damages to pasture and grazing lands. Ragwort contains pyrrolizidine alkaloids that are highly toxic to livestock, causing liver damage in horses and cattle. Goats may also be in danger of poisoning while sheep are generally not affected.

How do you get rid of it?

Manual Removal: Hand pulling is the most common removal method and is effective on small populations during the early stages. It is easier to pull the entire plant (including the roots) while the soil is wet, but seeds can remain viable in plants cut from roots. It is important to remove plants from the site and bury or burn them.

Spreading can be prevented by clipping or deflowering plants and burning them to eliminate seed set, but the main plant may continue to grow and flower each season.

It is also beneficial to re-vegetate areas along with native species and trees in addition to removal to prevent re-invasions.

Mechanical Removal: Plowing and mowing have proven unsuccessful in controlling ragwort and have actually distributed seeds and roots thereby contributing to larger infestations. It is possible to deplete reserves in ragwort plants through continuous mowings (preferably every six weeks during spring and summer months). Mowing during flowering might increase infestations (Bossard et al.2000).

Biological Control: Several USDA certified biocontrol agents have been released for controlling tansy ragwort. The cinnabar moth, Tyria jacobaeae, is a day-flying moth indigenous to Europe and Asia. The larvae of this plant feed on the flower buds, while also consuming the leaves and stems. However, this insect is often subject to disease, predation, and parasitism.

The tansy seedfly, Pegohylemia seneciella, is a small muscid fly common in the tansy flowers of France and Italy. This fly consumes the seeds of the tansy ragwort, which prevents its reproduction and spreading, but does not kill host plant.

Another host-specific ragwort pest is the tansy flea beetle, Longitarsus jacobaeae, whose larvae feed throughout the root crown and sometimes externally on the lateral roots. They also bore into the stem and leaf petioles for approximately 2-5 inches, causing the plant to wilt and die.

Author:
Unity Peterson, Invasive Plant Program Coordinator, Mattole Restoration Council, Petrolia, CA.

Photographs:
CDFA, 2001

References:
Bossard, CC., J.M. Randall and M. Hoshovsky. (eds.) 2000. Invasive Plants of California’s Wildlands. University of California Press, Berkeley, CA. Online version: http://groups.ucanr.org/ceppc/Invasive_Plants_of_California's_Wildlands/