In-Season Canopy Reflectance Can Aid Fungicide and Late-Season Nitrogen Decisions on Winter Wheat

Winter wheat (Triticum aestivum L) response to foliar fungicide and late-season N is inconsistent. We evaluated various late-season N fertilizer-by-foliar fungicide combinations to test whether wheat anthesis normalized difference vegetative index (NDVI) could aid fungicide decisions. Six site-years were conducted with N fertility > 120 kg N ha(-1) during 2012-2013 and 2013-2014 in Oklahoma, using a three-way factorial arrangement of a randomized complete block design with four replications. Fungicide treatment (with or without), foliar N source (urea ammonium nitrate [UAN] or controlled-release N), and N rate (0, 2.8, 5.6, or 28 kg N ha(-1)) were applied during anthesis. Statistical analyses were performed by site-year, by yielding environment (low [LY] < 3.2 Mg ha(-1) and high [HY] > 3.2 Mg ha(-1)), and pooled across site-years. Grain yield was 0.21 Mg ha(-1) greater due to fungicide in the pooled analysis, mostly led by the 0.59 Mg ha(-1) yield advantage in HY as opposed to non-significance in LY. Fungicide increased test weight in 6 to 7 kg m-3 across all analyses, and 28 kg N ha(-1) increased grain protein by similar to 10 g kg(-1) but caused leaf burn. Anthesis NDVI < 0.6 occurred when preanthesis abiotic stresses restricted yield potential, not warranting fungicide application. Fungicide can benefit grain yield and test weight and could be considered when anthesis NDVI > 0.6, but yield response will depend on grain-filling conditions. Foliar N rates needed to increase grain protein in a well-fertilized crop have potential for leaf burn.