Foliar Fungicide Effects On Gray Leaf Spot And Yield Of Hybrid Corn As Influenced By Application Timing Hybrid Characteristics And Production Practices

Abstract: Ohio ranks 9th among leading U.S. corn-producing states in total grain corn acreage. The corn crop adds an estimated $3 billion to Ohio's economy each year. Since the 1980s and 1990s when gray leaf spot, caused by Cercospora zeae-maydis, provoked widespread yield and economic losses in Ohio, foliar diseases have only been a concern in localized areas of the state. In most years, producers effectively manage foliar diseases by practicing some form of crop residue management, rotating corn with soybean, and planting resistant hybrids. However, without a major corn disease epidemic in more than a decade, the focus has shifted away from production practices geared to minimized disease-related losses. Since 2006, growers across the Corn Belt have been investing heavily in fungicide application. This is due in part to recent corn prices and the potential for greater disease development in a continuous-corn conservation-tillage cropping system, but most importantly, to industry claims of substantial yield increases due to the use of foliar fungicide, particularly the Quinone Outside Inhibitors (QoI). In Ohio, more than 650,000 hectares acres of corn were sprayed with fungicide during 2007. At an estimated application cost of $57 per hectare, this represented a total expenditure on fungicide of $37 M. Based on grain prices in that year, it would have required an estimated 375-501 kg/ha increase in yield to offset the cost of fungicide application. Results from university-based replicated trials suggest that the effect of fungicide application on yield is less clear-cut than industry data seem to suggest. In some university trials, positive yield responses were associated with disease control, in others there were no yield benefits even when diseases were controlled, yet in other trials positive yield responses were observed in the absence of high disease pressure. Since production practices have changed substantially since the available disease management recommendations were developed, there is a need to revisit these recommendations and develop sustainable management guidelines suitable for current production systems. Hence the objectives of the research presented in this thesis were to: investigate the effects of hybrid gray leaf spot resistance and yield potential, and fungicide application (product and timing) on the development of gray leaf spot and grain yield and yield components in a minimum-till/continuous-corn and a corn-soybean rotation cropping systems.