An agricultural sector model estimates impacts for hypothetical U.S. outbreaks of Ug99 wheat stem rust. Scenarios describe reductions in wheat output and exports beginning in 2013. The four year losses in the welfare of wheat producers range from $1.7- $11.6 billion (-15% to -107%). In scenarios reflecting alternate assumptions of disease spread, consumers benefit from embargoed crops remaining in the United States. The consumer surplus change varies between a gain of $4.6 billion (0.3%) when importing countries embargo U.S. wheat shipments and turn to other suppliers and a loss of $1.4 billion (-0.1%) when other countries continue importing the reduced supplies of U.S. wheat. Treatment costs are $139 million to $2.4 billion.