As the warm summer days draw nearer, the yellow buttercup-ridden pastures of spring are starting to return to their normal green color. Buttercup is, in my opinion, one of the most annoying weeds. It’s toxic to livestock, spreads aggressively, and is difficult to control. Although it’s dying back a bit now, buttercup is a perennial so although less visible it’s not actually gone!
There are many species of buttercup; the most common in the Mid-Atlantic area is bulbous buttercup (Ranunculus bulbosus). It is named such because the plant forms a bulb-like base, called a corm, just below the soil surface. The corm, which functions to store energy, is what gives buttercup its ability to survive the hot, dry summer and also to overwinter. The presence of the corm also makes it almost impossible to control buttercup by mowing. (Mowing can, however, help to prevent buttercup from spreading as new plants are produced by seed.)
The best way to control buttercup is by outcompeting it with a good stand of grass. New buttercup plants typically germinate in bare patches as plants have a hard time becoming established in taller vegetation. If you have unthrifty pastures that are bare in places or have not received any recent amendments, consider renovation in late summer. Buttercup seeds germinate in late fall, so ensuring healthy pastures before then will help prevent the weed from spreading. Be sure to keep pasture productivity high through the winter and early spring, too. Overgrazed pastures are much more likely to show heavy infestation in the spring.
In cases where pasture productivity is adequate and buttercup is still a problem, chemical control can be a useful tool. The best time to spray buttercup is March to early April, before it blooms but once the average daytime temperature is at least 60 degrees. According to University of Maryland guidelines, 80-100% control of buttercup can be achieved with herbicide combinations containing 2,4-D. Dicamba herbicides, like Banvel and Clarity, are equally effective when applied at a rate of 1.0 pounds active ingredient per acre. There are several other commercial herbicides that have 80-100% control of buttercup: Crossbow (2,4-D and triclopyr), Forefront (2,4-D and aminopyralid), Milestone (aminopyralid), and Surmount (picloram and fluroxypyr) are a few.
When determining which product is best for your operation, be sure to read product labels to find out the details about grazing and haying restrictions as they vary widely between these products. (A convenient comparison chart showing this information is available as Extension Bulletin 237, “Pest Management Recommendations for Field Crops,” available at the Extension Office.) Also keep in mind that some of these products will kill clover.
Buttercup is toxic to all species of livestock and can even cause dermatitis in humans if handled excessively. The toxin protoanemonin is released when the plant is chewed or otherwise wounded and is present in all parts of the plant. Animals that eat buttercup may suffer from blistering of the mouth and internal parts of the gastrointestinal tract, diarrhea, colic, and, in severe cases, death. Fortunately, most animals will not eat buttercup because it is unpalatable. (Animals that do not have access to adequate alternative forages are, however, more likely to consume buttercup.) The toxin becomes inactivated when dried so buttercup is not a concern in hay.
I know firsthand how frustrating it can be to control buttercup as it’s a weed I have struggled with in my own pastures. Hopefully, knowing a little more about it will give you the upper hand in controlling it this year!