Tansy Ragwort (Senecio spp.)
One of Oregon’s most invasive weeds, tansy, has aggressively multiplied in recent years. Once almost completely eradicated by biological controls and aggressive spraying, recent changes in climate conditions and a long wet spring have allowed for a resurgence of this aggressive and toxic plant. Chronic exposure to tansy can be lethal due to high levels of Pyrrolizidine Alkaloids (PA) mostly on the flowers and leaves. These toxins will cause liver failure and central nervous system depression in horses, cattle and small ruminants. Most animals will stay away from tansy due to its bitter taste, but with overgrazed pastures they become more appealing to the hungry individual. Manual removal and chemical application during the early spring and late fall are the best methods of control. Mowing without removal of the roots and especially during flowering and seeding will lead to further spread of this noxious weed.