Nitrogen and Tillage Effects on Wheat Leaf Spot Diseases in the Northern Great Plains

Abstract

There is a need for management practices in cropping systems that can reduce the impact of plant diseases. Leaf spot diseases on wheat (Triticum aestivum L.) were evaluated for 11 yr to determine the influence of tillage, N fertilization, and cultivar on disease severity in a long‐term cropping system project, which included two cropping systems {spring wheat (SWF)–fallow and annual cropping [spring wheat (SWA)–winter wheat (WWA)–sunflower (Helianthus annuus L.)]}. The major leaf spot diseases were tan spot and Stagonospora nodorum blotch. In low precipitation years, the impacts of management practices on leaf spot disease severity were minimal. No‐till (NT) did not consistently increase the severity of leaf spot diseases. During the drier years, NT had the advantage of conserving soil water while not increasing the risk to leaf spot diseases. When N treatments influenced leaf spot disease severity, higher levels of disease severity were associated with the low‐N fertilizer treatment compared with higher levels of N fertilization. When a tillage × N treatment interaction was significant, disease severity was higher with NT at the low N treatment, but at the high N treatment the differences among tillage treatments were greatly reduced or eliminated. This indicates an advantage of using adequate N fertilizer especially with NT under our environmental conditions. When differences in leaf spot diseases for cultivars were evident, Roughrider winter wheat had higher levels of disease severity compared with Norstar; however, the differences between the spring wheat cultivars Butte86 and Stoa were not consistent for both cropping systems. Producers should integrate a combination of management practices to develop a consistent long‐term strategy for disease management suited to their production system and location.