Noxious weeds in horse pastures...

Asked July 30, 2020, 2:18 AM EDT

We have a Global Federation of Animal Sanctuaries (GFAS)-verified equine sanctuary in Wilsonville, OR. Our pasture this summer, which only provides social time (our horses are well fed with hay/supplements a.m. & p.m. to keep pressure off the pasture), has had some False Dandelion and a few Tansy Ragwort. We have sprayed them with Weedmaster to kill the roots. As the flowers die and dry (they had not yet gone to seed when we sprayed, so were green, with no obvious seeds), will they spread when we mow/mulch the pasture with the dead/dried flowers in it? Or become mulch along with the grass? We also heard that spraying may make the weeds taste a little sweet, and actually attract the horses to eat them. Could you please clarify this process for us? What is the safest way to permanently kill/remove these unwanted plants from our pasture?

Clackamas County Oregon

1 Response

Hello,
False dandelion and tansy have been quite prolific this year. I have attached a couple of website links and information regarding how to handle these weeds.
One thing in particular to notice especially with tansy is that the sprayed and dead weeds are still toxic if consumed. So spreading the mowed vegetation will/can backfire on you. The best way is to manually remove the weeds. I have not found any information in my resources regarding the sweetening of the weeds after spraying.
https://weedwise.conservationdistrict.org/management/tansy-ragwort
https://pnwhandbooks.org/weed/problem-weeds/ragwort-tansy-senecio-jacobaea
I'm afraid mowing won't get the false dandelion since it lays so close to the ground. If the horses have access to hay and other food they may not eat any green plants that do emerge.
The problem with trying to eradicate these weeds is that everyone around you also has to eradicate them otherwise the seeds blow in on the wind and continually 'infest' your pastures. Spraying early in the spring and manually removing any weeds that get missed is the best management. But it is sad to say that it is extremely difficult to completely eradicate these weeds and not have to deal with them from year to year. It seems to be a never ending cycle.
Please let me know if you have any other questions. You can always email me at the email below for a direct conversation.
Good luck.
Dawn