Buttercup Control in Horse Pastures
Every spring, pastures around Pennsylvania turn a lovely shade of yellow. This usually means one thing - the buttercups are here! Unfortunately, for most of us, this is not a celebration but a lament. Buttercups are mildly toxic to horses, irritating their mucous membranes if chewed and causing gastrointestinal distress if large quantities are consumed. Luckily, the mouth irritation usually prevents horses from grazing on buttercups.
There are several species of buttercup (Ranunculus species) that grow in Pennsylvania, including bulbous buttercup, tall buttercup, creeping buttercup, and small flower buttercup. They can vary slightly in appearance, height, and even their lifecycle (annual vs. perennial). Some even flower in the fall.
Different buttercup species can be difficult to tell apart. Graphic by Laura Kenny.
The spring flush of buttercups usually precedes a flurry of Extension phone calls asking how to eliminate them. Well-meaning neighbors suggest liming to kill buttercups. Others skip right to herbicides, only to see disappointing results.
To control buttercups, farm managers need to consider soil fertility, mowing, and proper herbicide use.
While agricultural limestone is not toxic to buttercups, there is some truth to the idea that it can help with buttercup control. Buttercup proliferation can indicate poor soil fertility, allowing it to outcompete desirable grasses. The first step is to take a soil test to determine whether your pasture needs lime and fertilizer, and how much of each to apply. Read Liming and Fertilizing Horse Pastures for more information. Overgrazing may be a factor as well.
Mowing can help reduce buttercup spread. Once they have flowered, the plants are putting all their energy into producing seed for another generation. Cutting off the flowers before seeds are viable reduces seed drop. However, it does not kill the perennial buttercup species, which survive the winter using energy stored underground in their roots.
Herbicides can be a very effective control tool if used correctly. Unfortunately, once you see the yellow flowers, the optimal time to spray has passed. The most effective time to spray buttercups in Pennsylvania is mid-March to April (check with your local Extension agent if you are in another state). If you learn to identify the buttercup leaves when flowers are present, you will notice when they start to emerge in the spring before flowering.
Many buttercup species are perennial, so their leaves are still present in the fall. A mid-September to mid-October spray (again, in Pennsylvania) can damage the plants while they are sending energy reserves to the roots for overwintering.
The last critical factor is which herbicide to use. Not every herbicide is equally effective on every weed, so it is crucial to consult with an expert to identify the right one for your needs. According to Table 2.6-11 in the Penn State Agronomy Guide, buttercup is well-controlled by Crossbow 3E (containing active ingredients triclopyr and 2,4-D), Metsulfuron 60DF (containing active ingredient metsulfuron), Cimarron Max (contains metsulfuron, 2,4-D, and dicamba), and products with a combination of active ingredients 2,4-D and dicamba (ex: Weedmaster, but there are many options labeled for forage use). Keep in mind that each product has its own instructions and limitations, so read the label carefully before applying. If you are unfamiliar with herbicide use, read Using Herbicides on Horse Farms for an overview.
Buttercups are common in horse pastures in the spring, and should not be a cause for panic. However, they can be a sign that your pasture management needs attention to help grasses thrive and outcompete weeds.
