Originally written by James Doyle, former SDSU Extension Natural Resource Management Field Specialist.
Broadcast spraying is a common means of controlling undesirable, or perceived weedy plants in a pasture in South Dakota. Many producers broadcast spray with the intent of reducing broadleaf plants (or forbs) in favor of grasses for livestock grazing. Although well intentioned, broadcast spraying can have many negative consequences, some of which are not immediately apparent.
The first consideration should be whether there is actually a weed problem. Being able to accurately identify the plant species that are present, and whether they are native, introduced, or noxious species is an important first step. Many times, producers may think they have a weed “problem,” when in reality what they are seeing is a diverse native prairie plant community! While some plants may be weedy, overpopulated, or undesirable, many forbs have value either as livestock forage or for pollinators and wildlife. Spraying may indeed control undesirable broadleaf plants, but it will also negatively impact the desirable native forb species that are an important component of grassland communities. From a production perspective, many forb species are valuable as a forage at certain times of year, or livestock may be obtaining certain nutritional needs from them; for instance, they often have high crude protein percentages at certain growth stages. Without careful observation, it can be easy to miss these occasional grazings and assume that cattle are not utilizing them at all. Similarly, even if cattle do not utilize a given species, several forb species are highly valuable as wildlife food and can provide important forage resources in the winter. Finally, many of these flowering plants are extremely important for pollinators due to their flowers and nectar. Many pollinators have complex habitat requirements and removing native forb species from rangeland can drastically reduce pollinator habitat quality.
A consistent spray program is targeting a symptom – it does nothing to address the underlying cause of pasture conditions. One of the most important factors is matching the stocking rate with the production of the land. If a pasture is continuously overgrazed, conditions will continuously be right for weed infestations, which will continuously require management. Season long grazing can also help set the stage for over-utilization of desirable species and under-utilization, followed by proliferation, of less desirable species. All plant species are filling certain ecological niches that include both above- and below-ground factors; as such, simply spraying to reduce an unwanted plant will not necessarily result in increased production of desirable species. Producers should critically analyze their management systems and try to identify certain factors that may be contributing to a weed issue, and then find solutions to address those factors. Additionally, having a goal for pasture condition can help with defining the necessary actions to reach that objective.
Another important consideration is the economics of broadcast spraying. Spraying an entire pasture, whether aerially or on the ground, is not a cheap undertaking. It is very uncertain whether any increased grass production as a result of the spray program is enough to make up for and provide an increased return on the investment and labor involved in spraying; with current cattle prices, this seems unlikely. Producers should be wary of jumping in to a spray program with the assumption that it will automatically pay for itself with improved production of grass that will ultimately be realized on the check from the sale barn.
In closing, broadcast spraying of pastures may not be necessary, or beneficial in many situations. Changing management can improve pasture conditions, while simultaneously improving the economics of a grazing enterprise. A simple grazing rotation can allow for better control of the timing, intensity, and duration of grazing along with allowing rest and recovery periods for desirable plants. Multi-species grazing can be another tactic to consider. By bringing in a new species of livestock (typically sheep or goats) that utilize different types of forage than cattle, producers can effectively turn these “unwanted” forages into a resource that can generate additional revenue. This is not always a simple undertaking, and will require careful thought and management, but it is certainly worth considering. It is important to note that landowners are required to manage noxious weeds on their property. Mowing/clipping or spot spraying can also be an important tactic to target noxious weeds, or specific undesirable species, that can limit many of the undesirable outcomes of whole-pasture spraying.