By Scout Nelson
Leafy spurge is one of the most difficult weeds affecting pasture and rangeland areas in South Dakota. This invasive plant spreads quickly, competes with desirable grasses, and reduces the productivity and value of grazing land.
Research conducted in South Dakota by Eric Jones, Assistant Professor and SDSU Extension Weed Management Specialist, along with Jill Alms and David Vos, explored new options for managing leafy spurge in pasture and rangeland environments.
Their work evaluated whether combining two herbicides, saflufenacil, and imazapic, can improve weed control compared to using either product alone.
Herbicides remain one of the most widely used weed management tools in pasture and rangeland systems. Traditionally, many leafy spurge management programs rely on herbicides such as picloram and 2,4-D because they control broadleaf weeds while remaining relatively safe for grasses. However, researchers are exploring additional options that may improve effectiveness and help diversify management programs.
Saflufenacil is a herbicide commonly used to control broadleaf weeds. Because it has limited activity on grasses, it can be applied in pasture and rangeland settings without causing major damage to desirable grass species. Imazapic is another herbicide that has shown activity on leafy spurge. Researchers wanted to learn whether combining these products would provide stronger weed suppression.
Field trials were conducted in South Dakota during 2023 and 2024. The study included research sites in Codington County and Brown County. Leafy spurge plants were treated with saflufenacil alone, imazapic alone, or a mixture of both products. Researchers then evaluated weed control one year after treatment.
The results showed clear differences between treatments. The herbicide mixture provided the highest level of leafy spurge control. One year after application, the saflufenacil and imazapic combination achieved approximately 85% control. In comparison, neither herbicide applied alone provided more than 63% control.
Researchers also measured changes in stem density, which is an important indicator of weed suppression. The herbicide mixture and imazapic alone produced the greatest reductions in stem numbers, while saflufenacil alone provided less reduction. Lower stem density can help reduce competition with desirable vegetation and improve pasture conditions.
Plant height was also evaluated during the study. Although all herbicide treatments reduced leafy spurge height to some degree, there were no significant differences among treatments. This suggests that surviving plants may continue to regrow at similar rates regardless of the treatment used. As a result, additional management practices may be necessary to prevent future spread.
The study also compared the results with previous leafy spurge research. Earlier studies have shown that treatments containing picloram or picloram plus 2,4-D provide between 56 and 83% control one year after application. The results from this research indicate that the saflufenacil and imazapic mixture performs within a similar range of effectiveness.
Even though the herbicide combination delivered strong control, complete elimination of leafy spurge was not achieved. Stem reductions reached about 79%, meaning some plants survived and may require future treatment. Researchers emphasize that follow-up management remains important for long-term success.
Another benefit of using herbicide mixtures is that they may reduce selection pressure on weed populations. Repeated use of the same herbicide or mode of action can increase the risk of reduced effectiveness over time. Including multiple modes of action can help diversify management programs and support sustainable weed control strategies.
Researchers suggest that future studies should evaluate how saflufenacil performs when combined with other commonly used pasture and rangeland herbicides. Additional research may also help determine whether similar benefits can be achieved on other troublesome weed species.
Photo Credit: pexels-moh-adbelghaffar
Categories: South Dakota, Education, General