摘要：Leafy spurge (Euphorbia esula L.), a widely established exotic, noxious, perennial weed, is a major threat to rangeland and wildland in the Upper Great Plains. Chemical, biological, and cultural control methods have limitations in their applicability and effectiveness in treating leafy spurge. However, many of the constraints prohibiting the use of herbicides, tillage, and biological controls do not apply to sheep grazing. Sheep grazing, while known to be effective in controlling leafy spurge since the 1930s, has lacked widespread adoption as a leafy spurge control. A deterministic, bioeconomic model, incorporating relationships between sheep grazing and leafy spurge control, grass recovery, and forage use by cattle, was developed to evaluate the economic viability of using sheep to control leafy spurge. Discounted annual control costs were compared to discounted annual control benefits over 5-year, 10-year, and 15-year periods. Various scenarios were developed depicting likely situations involving adopting a sheep enterprise or leasing sheep for leafy spurge control. Situational factors considered included fencing expenses, debt considerations, grazing values, infestation size, infestation canopy cover, rangeland productivity, and flock performance. Two levels of flock profitability, one based on a level of proficiency achieved by sheep ranches and one substantially lower than typically achieved in the sheep industry, represented best-case and worst-case situations, respectively. In the best-case situations, using sheep to control leafy spurge was economical in all of the control scenarios examined. However, in the worst-case situations, economics of using sheep to control leafy spurge were mixed across the scenarios examined. Leafy spurge control with poor sheep management, high fence expense, and unproductive rangeland generally was not economical. However, situations with low fencing costs, moderately productive rangeland, and poor sheep management resulted in less economic loss than no treatment. Although many of the key relationships tying leafy spurge control to grazing benefits remain unquantified, the economics of sheep grazing were positive across many of the scenarios evaluated in this study. Actual returns from leafy spurge control for most ranchers will likely fall between the two extremes examined. As a precaution, careful evaluation using site- and rancher-specific inputs would be recommended before implementing sheep grazing as a leafy spurge control method.
