We develop a theoretical and empirical model to measure the benefits and costs of policy options for controlling a seedborne, imported fungus, Verticillium dahliae, seriously affecting lettuce production in California. In 1995, the disease Verticillium wilt, caused by the fungus V. dahliae, unexpectedly appeared in a lettuce crop in Watsonville, Santa Cruz County. Since then, the disease has spread rapidly through the Parajo Valley, the prime lettuce production region of California. Plant pathologists have determined spinach seeds to be the primary pathway by which the fungus is introduced to the soil (Atallah et al., 2010). Once introduced, the pathogen persists in the soil for many years, affecting subsequent crops. We develop a simulation model to describe growers' profit maximizing decisions regarding which crops to plant, the timing of the plantings, and efforts to control the disease. We also estimate a structural econometric model explaining crop choice decisions made by growers in Monterey County. A simulation model allows for the incorporation of biological parameters estimated from the work of plant pathologists. In addition, we can compare different scenarios, in particular those that growers are hesitant to implement in their fields without knowing the impacts.