Tansy ragwort, Senecio jacobaea, is a noxious weed with poisonous alkaloids that cause irreversible liver damage to animals (and humans) if consumed. All of its parts are toxic, with the highest amount of alkaloids in flowers, then leaves, roots and stems. The plant remains toxic when dried in hay.
In the summertime, with showy yellow flowers standing tall, tansy ragwort is easy to identify. However, in July and August the only management option is to dig up the plants and haul them to a landfill. This discourages many landowners from working to remove the weed.
In the spring however, there are several effective management options. Landowners should walk their fields and identify the plant. In the spring, tansy is in the rosette stage with ruffled dark green leaves that may have a reddish tinge.
Biological control is also at work in the spring. The ragwort flea beetle, Longitarsus jacobaeae, is out in force devouring tansy plants. The adults feed on the leaves and the larvae damage the roots. Look for these golden to light-brown beetles on and under the leaves of the plants. If you find them on your site, consider leaving some tansy ragwort as a food source, especially in areas that may not impact your livestock.
Sheep tolerate the toxic alkaloids and can also help manage tansy ragwort. However, they may choose to graze other desirable plant species before consuming large amounts of tansy. Nevertheless, grazing sheep on your property will help with longterm weed management.
Since the ground is moist and the plants relatively easy to pull, spring is the best time to manually remove tansy. Remove the fleshy taproot or the plant will regrow. Young plants could be added to a hot compost system, buried or added to a burn pile. Mowing stimulates more vegetative growth.
All broadleaf herbicides labeled for tansy ragwort are most effective on young, actively growing plants. Since Oregon spring weather is unpredictable, plan ahead and watch for a window of calm, dry weather to spray. The Pacific Northwest Weed Management Handbook includes a list of labeled herbicides for tansy ragwort.
Tansy ragwort infestations are often the worst in overgrazed pastures with bare or compacted soil. Along with managing weeds this spring, also consider ways you can manage pastures that will enhance forage growth.
