EFFECT OF SPLIT APPLICATIONS OF FENPROPIMORPH-CONTAINING FUNGICIDES ON SENSITIVITY OF ERYSIPHE-GRAMINIS F SP TRITICI

A held trial was conducted in the south of the Netherlands over a peri od of 3 years (1992-94) in order to test the effect of fenpropimorph-c ontaining fungicides on the sensitivity of Erysiphe graminis f.sp. tri tici 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 applic ations. The sensitivity to fenpropimorph of the mildew population in p lots treated with normal applications of both fungicides did not chang e during the growing seasons of the years investigated. In contrast, t he sensitivity of the mildew population from plots treated with split applications of Corbel became significantly lower. A significantly low er sensitivity was also found in the mildew population from plots trea ted with split applications of Tilt Top in 1993 and 1994. These result s indicate that split applications can increase the rate at which E. g raminis f.sp. tritici can become less sensitive to fenpropimorph. Beca use maintenance of sensitivity of the pathogen population is valued hi ghly, the split application strategy of fenpropimorph-containing fungi cides is not recommended for wheat powdery mildew control.