Assessing economic impacts of biological control of weeds: the case of leafy spurge in the northern Great Plains of the United States.

Leafy spurge (Euphorbia esulaL.), a perennial weed native to Europe and Asia, has become a serious problem for ranchers and land managers in the northern Great Plains region of the United States. Potential economic benefits (i.e. gross benefits, not including the cost of biological control) from biological control of leafy spurge in the four-state region of Montana, North Dakota, South Dakota and Wyoming are estimated. Biological agents were predicted to control about 65% of the region's leafy spurge infestations—about 1·2 million acres (497 000 ha)—by the year 2025. Direct economic impacts from control were estimated to total about $19·1 million annually, and secondary impacts were estimated at $39·3 million, for a total annual economic impact of $58·4 million.