Fungicides for Winter Wheat

Topic Relevance Foliar diseases often reduce grain yields of winter wheat in the southern Great Plains, with some individual year yield losses in excess of 10%. At current prices, the gross value of these losses for the region could exceed a quarter of a billion dollars annually. Historically, use of foliar fungicide applications to manage these diseases has not been common in the region. As a result, management of foliar diseases has largely relied on genetic resistance and other cultural practices such as planting date and crop rotations. However, in Europe, where wheat yields average more than twice the U.S. average, fungicides are applied to over 95% of the wheat area and are credited as one of the major factors influencing increases in European wheat yields since the 1970s (Gianessi and Williams 2011). Recent wheat prices and decreasing fungicide costs have generated interest among U.S. wheat farmers in evaluating the economics of fungicide treatments. Wheat grain yield response to fungicide treatment is variable, and depends on several factors including incidence and severity of specific foliar diseases, cultivar disease resistance, timing and leaf coverage achieved by fungicide application, yield potential, and environmental conditions. In addition, if a ground applicator is used to apply the fungicide, the wheel tracks or the use of tram lines may influence yield. Alternatively, if an aerial application is used, the cost consequence of applying a sufficient water volume to achieve adequate plant leaf coverage is critical. Some research has been conducted to determine the expected returns to fungicide treatment as part of a disease management strategy. However, variability of expected returns resulting from alternative management strategies has not been considered. The objective of this research is to determine the expected net returns to fungicide treatment on hard red winter wheat cultivars with differing levels of genetic resistance to foliar diseases in the southern Great Plains, and to determine if fungicide treatment is an economically optimal management strategy for several levels of risk aversion. Research Methods Hard red winter wheat grain yield data were produced in field experiments conducted at two locations during seven production seasons, from 2005 to 2012. Varietal resistance for each wheat cultivar was determined based on average disease resistance rating to leaf rust, stripe rust, and powdery mildew. Two fungicides were rotated between the two locations and applied at recommended rates at Feekes growth stage 9.5 to 10. SAS Proc Mixed was used to determine grain yield response to fungicide treatment, varietal resistance level, and their interaction. Least-square mean grain yields were estimated and compared for differences between fungicide treated and nontreated plots by varietal resistance level for each year and location. A partial budgeting approach was used to determine the expected net returns for each disease management strategy at both locations. Expected yields were adjusted for losses expected to occur from wheel tracking and/or tram lines required for ground application of fungicide. Given the lack of information about these losses, sensitivity analysis was done across various levels of yield losses. Fungicide treatment cost included the per acre cost of chemical as well as the per acre rental rate for ground application. Risk analysis was conducted using SIMETAR (Richardson, Schumann, and Feldman 2001). Assuming each season was equally likely, and the years of the study were representative of the entire distribution, cumulative distribution functions of net returns to alternative strategies were evaluated using stochastic efficiency with respect to a function (SERF). SERF was used to determine the fungicide treatment cost that would entice wheat producers to use fungicide for several levels of risk aversion. Potential for Generating Discussion Fungicide treatment on winter wheat is a timely topic that has the potential to generate discussion. Fungicides are not commonly used among U.S. wheat producers in the southern Great Plains. However, results of recent literature, including this analysis, suggest potential economic benefits to treating winter wheat with fungicides. In addition, results of this analysis suggest that the utility of risk averse decision makers would generally be increased by strategies that include fungicide treatment given its tendency to protect from the downside risk of large yield losses in years of high disease incidence and severity. These results may facilitate a discussion as to the role of fungicides in winter wheat production in particular and chemical use in production agriculture in general. Other facets of this research, such whether or not U.S. farmers could benefit from using tramlines, also have potential to stimulate discussion.