Tansy ragwort used to be everywhere in Oregon. Well, now it’s back, according to Oregon State University.

The non-native weed was introduced to Oregon in the 1920s, and without natural enemies to keep it under control, it spread everywhere. This was a major problem for farmers and ranchers, as tansy ragwort is deadly poisonous to cattle and horses. State agriculture officials fought back starting in 1960 by importing beneficial insects from Europe — the same insects that keep tansy ragwort under control there. It worked. The introduction of the cinnabar moth, the tansy ragwort flea beetle and a seed head fly was a major success for ODA, and tansy ragwort was considered under control in the 1980s. Unfortunately, in 2005 and again this year, weather conditions have conspired to let the weed stage a comeback. The cold and wet spring we experienced this year is not only good for tansy ragwort, but bad for the insects that control it.

So what to do if your land has tansy ragwort? First, if you have horses or cattle, make sure they don’t graze in the affected areas. If they have and show symptoms, do not wait to call a veterinarian. Second, download this PDF booklet from ODA that has tips on controlling the weed. It’s not advised to use chemicals on it in the summer. They’re more effective in the fall. Further, mowing is not advised, as it just disperses seeds which have a long life in the soil. Oddly, sheep are not harmed by the toxins in tansy ragwort, so some farmers have been known to let them graze and clear the weed out.

For more information, read this very informative article published by the Oregon State University Extension Service.