tansy

Asked October 21, 2018, 9:31 PM EDT

Is the state of OR going to pursue bringing back the cinnibar moth/tansy worm? They are the best things to control the over abundance of tansy. They did an excellent job of almost irradicating tansy back in the 70's' I remember as a kid, spending all summer pulling that weed on my uncle's farm. I remember it being illegal not to control tansy on your place. My uncle had 150 acres of the stuff. (he even spent 2 days in jail for 'not controling his tansy). He said the seed can stay in the ground for years. we pulled for several years before the moths showed up. They cleaned it right up. Now it's making a comeback. Bring on the moths/worms!!!!

Clackamas County Oregon

1 Response

Thank you for your question. It is true that prior efforts to introduce the cinnabar moths was successful, as this article details: https://extension.oregonstate.edu/pests-diseases/weeds/tansy-ragwort

However, as with many 'cures,' an unintended consequence of introducing them was this: "While largely considered a biological control success story, the cinnabar moth larvae can feed on a native plant in Oregon, arrowleaf groundsel, as well as the weed species of groundsel... And the cyclic fluctuations in the growth of tansy ragwort may require patience while cinnabar moth populations increase to meet the need." (http://oregonstate.edu/dept/nurspest/cinnabar_moth.html)

So, the strategies suggested in the first article may be the only long-term mechanisms for the long haul. There are few 'silver bullets' in horticulture!