Limitations to implementation of yellow starthistle control measures by ranchers

Although significant research has been devoted to the control of the invasive weed, yellow starthistle (Centaurea solstitialis), its range is increasing in the Sierra Nevada foothills. The invasion often heavily affects cattle ranchers, but many factors compromise their ability to respond to it. We used surveys and interviews to document 202 ranchers' weed control efforts and to identify potential logistical limitations to effective yellow starthistle control. Overall, 83.2% of ranchers with any history of yellow starthistle infestation had attempted control, employing 19 methods study-wide. Surveyed ranchers reported significantly greater efficacy for hand-pulling and application of Transline® than other control techniques. In addition, interviewees exhibiting early response to the invasion experienced reduced negative impacts from yellow starthistle. Ranchers rated control techniques learned from agricultural advisors as more effective than those learned elsewhere. Our interviews revealed that limitations to “perfect” implementation of yellow starthistle control strategies arise from a myriad of factors, including incomplete knowledge (e.g. uncertainty about control methods or timing), complexity of heterogeneous landscapes (localized inapplicability of available methods), inconsistent implementation of methods (e.g. nonconsecutive control years with a long-lived seed bank), and lack of long-term planning and investment in weed control (primary use of ad hoc control efforts). These hindrances obstruct the successful implementation of control methods developed by research scientists. Such disparity between science and practice contributes greatly to the continued increase of yellow starthistle within this region despite tremendous control resources invested by land managers and state agencies.