I don’t know about you, but when I consult a list of all of the Kentucky pasture plants that are potentially toxic, it amazes me that livestock ever survive. Buttercup is one of those weeds. Buttercup contains the toxin ranunculin which is a blistering agent. Ingested in large quantities, it can be fatal. We can find four species of buttercup in Kentucky, but species differ in their toxicity. I can almost hear you say ‘What? Buttercup is toxic? But it is everywhere!’ It does seem to be everywhere, especially in fields that have been grazed closely during the fall and winter. This low growing pasture weed is very visible right now due to its bright yellow flowers.
Livestock will avoid buttercup in pasture, even when it seems to dominate the stand. Buttercup is not a problem in hay because the ranunculin is detoxified by the curing process. This spring, we received questions from multiple sources about the toxicity of buttercup in small grain silage in round bales. At first, this seemed to be one of those questions for which there was no good answer.
Logically, it would seem that if ranunculin was detoxified by the curing process, the wilting required before making baleage (round bale silage) would also detoxify the buttercup. There are no documented cases of buttercup poisoning at the UK Veterinary Diagnostic Laboratory, indirect evidence that buttercup toxicity is not a problem in our stored forage. However, neither provide the firm evidence that we needed to say that buttercup was not a problem in silage.
Dr. Ray Smith, my fellow UK forage extension specialist in Lexington made the contact with researchers in Switzerland, who remembered an old paper on buttercup detoxification in silage. The 1992 research paper (written in German) found that ranuncilin levels were reduced by 90% in silage compared to fresh forage. The most toxic species of buttercup in this study was not one commonly found in Kentucky.
Although it is good to know that buttercup is not toxic in silage, it is still not a desirable plant in pastures or hayfields. Buttercup emerges from seed in the fall or late winter and can be controlled by numerous broadleaf herbicides. Control is more effective in February through April when buttercup is small but before the yellow flowers emerge. For more information on weed control in grass pastures please see Weed Management in Grass Pastures, Hayfields, and Other Farmstead Sites (http://www2.ca.uky.edu/agcomm/pubs/agr/agr172/agr172.pdf) or Broadleaf Weeds of Kentucky Pastures (http://www2.ca.uky.edu/agcomm/pubs/agr/agr207/agr207.pdf).
So buttercup is still potentially toxic and a problematic weed in pastures and hayfields. But at least we now have solid evidence that it is detoxified in both hay and silage.
Happy foraging. ~ Dr. Jimmy Henning for Farmer’s Pride