Mark Renz, Extension Weed Scientist, and Kevin Shelley, UW NPM Program
Buttercups, have been showing up this spring in pastures and hayfields in southern Wisconsin. While Wisconsin has 18 species of buttercup, little leaf buttercup (Ranunculus arbotivus) is the most commonly seen in production fields. This species is native to Wisconsin and can behave as a biennial to short term perennial. While this plant can be found every year in the state (common in our forests), it is probably more common this year in hayfields and pastures due to overgrazing and poor regrowth from the summer droughts of 2012 and 2013. These conditions likely allowed for establishment and increased populations compared to “normal years”.
While this plant competes with desirable forage, the reason for controlling this native weed is that buttercups contain a toxic compound to all classes of livestock. This compound causes inflammation of the mouth and intestine when ingested, and if enough is ingested (>20% of diet) death can result. Fortunately little leaf buttercup is one of the least toxic buttercup species, with no direct evidence of mortality from ingestion known in the United States. Additionally, this plant is rarely eaten by animals as it has a very bitter flavor. Thus pasture animals have low risk of poisoning unless a producer grazes in a manner that reduces selectivity (e.g. mob grazing).
A fairly heavy infestation has been observed (see picture) in first crop alfalfa hay in western Columbia County near Lodi this spring. This poses a bigger problem as the cut forage is a mixture of alfalfa and buttercup. This mixed ration, if fed directly to animals, could reduce their ability to avoid buttercups. While it is unlikely that the amount of buttercups ingested will result in mortality, reduction in performance or changing in milk flavor could result. In this situation we recommend drying the hay before feeding it to livestock as the poisonous properties and bitterness are destroyed when hay is cured.1,2 This problem is an issue in the first cutting of the year, but buttercups are rarely present in subsequent harvests as regrowth is minimal.
In pastures, a range of broadleaf herbicides are available and effective on buttercups, but will also injure/kill legumes. Spot treatments of herbicide or mowing will prevent any toxicity. In alfalfa, buttercup presence is often a symptom of thin stands or fertility problems. Check these prior to using herbicides, as effective options (e.g. Velpar) should be applied pre-greenup and typically have long plant-back intervals. Consult UWEX A3646 Pest Management in Wisconsin Field Crops for general guidelines3.
1 Royer, F. and R. Dickinson, 1999. Weeds of Canada and the Northern United States. Pp. 116-117.
2 University of Pennsylvania, 2014. http://research.vet.upenn.edu/PoisonousPlantsofPA/Ranunculus/tabid/5473/Default.aspx
3 Cullen, E. et al. Pest Management in Wisconsin Field Crops, 2014. UW Cooperative Extension publication A3646, pp. 177-189. http://learningstore.uwex.edu/Assets/pdfs/A3646.pdf