By Dwight Lingenfelter
Pastures that are yellow because of buttercup infestations are a common sight during spring. However, this should not be considered a badge of honor. In general, pastures that have dense populations of buttercup and other weed species in most cases are lacking proper management. Often it is a sign of over-grazing and a poor stand of desirable forage. Good agronomic practices are key to a healthy, persistent forage stand and should include proper fertility and soil pH levels and grazing and mowing management, along with effective and properly timed herbicide applications.
Buttercup species that are common to PA include, bulbous buttercup (Ranunculus bulbosus), creeping buttercup (Ranunculus repens), tall buttercup (Ranunculus acris), and small flower buttercup (Ranunculus arbortivus). Most of these have a perennial lifecycle, however some can behave as a winter annual. In general, they are most actively growing during the fall and early spring and then flower during the spring season. Therefore, mowing fields as low as possible during the early spring before they start to flower can help reduce seed production. Routine mowing can also occur during the rest of the growing season to thwart weed seed production and encourage pasture growth. The question about when the optimal time is to spray herbicides --- the short answer is early spring. The use of herbicides during early spring (Mid-March thru April) is the most effective time to control buttercup populations. Treatments applied in fall (mid-September thru October) are not as optimal as a spring application but can still provide control. Herbicides such as 2,4-D (2-3 pints/acre), 2,4-D (1 quart) + dicamba (1 pint), metsulfuron/MSM (0.2-0.3 oz), or Crossbow (2-3 quarts) are commonly used to control buttercup. When spraying in the spring make sure the air temperatures are at least 50F or more for a few consecutive days for effective control. Spraying when buttercup is flowering usually does not provide effective control. Keep in mind, these treatments will severely injure or kill any legumes in your stand. If you are concerned about keeping white clover in the mix, 2,4-D (1 pint) could be used. However, by using this tactic, buttercup will likely only be suppressed, and clover growth can be temporarily stunted. So be sure to consider all the tradeoffs when using this practice.
Source : psu.edu