Many preferred sweet corn hybrids grown in New York are susceptible to common rust, and therefore growers must use fungicides for effective disease management. Strobilurin fungicides work well, but are too costly to be applied to the crop more than once a season. The question then becomes one of the best timing to apply that single spray. If the application is made too early, rust may still build to damaging levels; if too late, rust levels may not be reduced sufficiently. A model was constructed to simulate common rust epidemics, and used to examine whether fungicide applications made according to pre-specified disease thresholds resulted in cost-effective disease control. Simulations were done for action thresholds between 1 and 15% disease severity. Simulation results indicated a linear increase in the chances of cost-effective rust control when the action threshold was increased from 1 to 15%. In summary, simulation results suggest that a strobilurin fungicide application made during the early stages of a rust epidemic is at greater risk of losing money because of ineffective disease control compared to waiting to make the application if and when disease severity increases to higher levels.