This blog post was first released by the Washington State Noxious Weed Control Board on June 26, 2015.
Noxious weed kills livestock, contaminates hay, and taints milk and honey.
Livestock owners and hay growers are preparing for an early season for tansy ragwort (Senecio jacobaea), a noxious invasive plant from Eurasia that can kill livestock and contaminate hay. It can also give honey and milk a bad taste, making them unsellable. Alkaloids in all parts of the plant accumulate and become toxic in the liver, irreversibly damaging it. The effect is worst in horses and cattle but can also affect goats, pigs, and deer. In horses and cattle, liver failure makes them “go upside down, feet in the air, and bleeding from both ends,” says Rick Johnson, noxious weed coordinator for Thurston County, where tansy ragwort is flowering at least 1 month earlier than usual, requiring prompt treatment.
Control of this Class-B noxious weed is required in all eastern Washington counties, except Klickitat, and in many western Washington counties. Even where control isn’t required, however, all land owners can help make pastureland and forests healthier by removing tansy ragwort before it flowers and sets seed. One plant can produce 5,000 to 200,000 seeds a year, which can spread more than half a mile via wind, water, animals, and clothing and vehicles.
“It’s important to control tansy ragwort on your property—even if you don’t own livestock or produce hay,” says Washington State Noxious Weed Control Board Executive Secretary Alison Halpern. “The seeds spread easily, so it’s important to stop tansy ragwort at its source, no matter where it originated. Your local horse owners, dairy farmers, hay and honey producers will really appreciate your efforts.”
Tansy ragwort invades roadsides and in heavily grazed pastures, fields, and cleared forests, where grass and other plants are sparse. Usually a tap-rooted biennial, it forms a rosette with red stems and coarse, ruffled leaves its first year. In its second year, plants grow one or more leafy stems up to 4 feet tall and develop flat-topped clusters of yellow, daisylike flowerheads. Each flowerhead is really a composite of tiny florets surrounded by 13 ray flowers, which look like petals. Tansy ragwort can also grow as a perennial, coming back year after year until it finally sets seeds and dies.
The most important time to control tansy ragwort is early in the year, before horses and cattle become accustomed to its strong odor and bad taste, says Thurston County’s Johnson. For small infestations, mechanical controls work best. Note: When working with tansy ragwort, be sure to wear gloves and other protective clothing. Mechanical controls include pulling or digging tansy ragwort, preferably before the plants flower. Be sure to remove the taproots, which can resprout. If you miss that time window, you can cut off flowerheads and put them, tightly bagged, in the trash. Or you can pull new rosettes in fall. Mowing, however, is not a good option as it can cause tansy ragwort to become perennial. Larger infestations might require using several methods of control.
Several herbicides can effectively kill plants before they flower. To limit the amount of chemicals you use, combine herbicides with other methods of control. Contact your county noxious weed board for information on selecting and applying herbicides for your property and to learn more about integrated vegetation management practices. Sheep, seldom poisoned by tansy ragwort, can reduce seeding. Overgrazing, however, can backfire, increasing infestation after the animals are removed. Biocontrol insects that specifically target tansy ragwort can help reduce infestations without damaging other plants, although they won’t completely eliminate the tansy ragwort population. For more information on these biocontrols, contact the WSU Extension Integrated Weed Control Project. Together with these methods, mulching or thickly planting fast-growing annual species can help knock back tansy ragwort emergence by limiting sunlight and bare ground. Once you have achieved control, you can replant species you prefer.
Properly disposing of tansy ragwort is one of the most important steps in its control. Put all parts of the plant in plastic bags, and throw them in the garbage, where animals can’t eat them and seeds can’t resprout. Never burn tansy ragwort, as the fumes can cause severe rashes.