Yield loss and fungicide control of stem rust of wheat

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Abstract
Yield loss in wheat from natural infections with Puccinia graminis f.sp. tritici ranged from 10 to 45% in 3 experiments over 2 years. Fungicide reduced subsequent stem rust severity on plant parts that were only slightly infected at the time of fungicide application, but was not effective on plant parts that were more heavily infected when treated. Fungicide control of stem rust was economic in a range of situations. Fungicide applied at head emergence with low disease incidence (5% of stems) increased yield by 0.3 t/ha. When applied prior to head emergence with high disease incidence at low disease severity, yield increased by 0.8–1.5 t/ha, depending on duration of control. At a high disease incidence and moderate disease severity, yield increases of 0.4–0.6 t/ha were observed. Grain quality was also significantly improved with fungicide. Fungicide was more effective when applied immediately following detection compared with a 3-week delay. Folicur was more effective at reducing disease and increasing yield or quality than Impact or Triad.