A bioeconomic model is used to examine efficient dynamic and static phytosanitary policies (cold treatment periods) designed to maximize the annual present value of net monthly U.S. welfare associated with trade in commodities that serve as hosts for the Mediterranean fruit fly (medfly). Accounting for the presence of the current U.S. medfly detection and control program, efficient dynamic and static policies require less cold treatment and increase U.S. welfare 9% and 3%, respectively, relative to the current minimum 14-day treatment period. The potential value of adjusting treatment periods regularly using available information on medfly pressure abroad is shown to be nontrivial.