Effect of split applications of fenpropimorph-containing fungicides on sensitivity of Erysiphe graminis f sp tritici

A field trial was conducted in the south of the Netherlands over a period of 3 years (1992-94) in order to test the effect of fenpropimorph-containing fungicides on the sensitivity of Erysiphe graminis f.sp. tritici to fenpropimorph. In general, use of split applications resulted in a better protection against wheat powdery mildew than use of normal applications. This is ascribed to a better timing of the split applications. The sensitivity to fenpropimorph of the mildew population in plots treated with normal applications of both fungicides did not change during the growing seasons of the years investigated. In contrast, the sensitivity of the mildew population from plots treated with split applications of Corbel became significantly lower. A significantly lower sensitivity was also found in the mildew population from plots treated with split applications of Tilt Top in 1993 and 1994. These results indicate that split applications can increase the rate at which E. graminis f.sp. tritici can become less sensitive to fenpropimorph. Because maintenance of sensitivity of the pathogen population is valued highly, the split application strategy of fenpropimorph-containing fungicides is not recommended for wheat powdery mildew control.