Even though fungicide applications have been shown to provide effective control, the resulting yield gain has not always been sufficient to offset the associated costs. According to Ward et al. (65), yield response to fungicide treatment may be a function of the time of initial application, the amount of disease at the time of application, the duration of the protection offered by the fungicide, and control through physiological maturity. In South Africa, the gain in yield from fungicide treatment often exceeds the breakeven point needed to cover chemical
and spray application costs, making chemical control economically feasible (63). One-, two- and three-spray application programs all provided cost-effective disease control, exceeding the breakeven increase in grain yield (64, 65). In the United States, chemical control of gray leaf spot in grain production is not always economically feasible. Munkvold et al. (42) estimated that the cost of a single application of propiconazole may provide economic benefit to farmers in Iowa when a susceptible hybrid is planted. A single fungicide application may be profitable for gray leaf spot management in maize grown for grain in Iowa; however, the probability of profitability is strongly dependent on the yield potential and susceptibility of the hybrid planted (42). Munkvold and coworkers (42) reported that the probability of achieving a net return with a single application ranged from 0.06 to more than 0.99, and that the probability was almost always higher using one application compared to the probability of receiving a net return when two fungicide applications were used. Due to the high value of the crop, fungicide application is often more profitable in maize seed production (41, 67)