Sensitivity and efficacy of the succinate dehydrogenase inhibitor fluxapyroxad, against raspberry spur blight fungus Didymella applanata

Didymella applanata, the causal agent of raspberry spur blight, is a destructive plant pathogen that can cause serious reductions in total yield. The use of fungicides plays a crucial role in successful control of the pathogen. The sensitivity of 94 isolates (66 collected during 2013 and 28 in 2017) of D. applanata to the succinate dehydrogenase inhibitor, fluxapyroxad, was evaluated in this study. In addition, the efficacy of fluxapyroxad in raspberry spur blight control in the field was determined. The isolates tested in this study showed different sensitivity to fluxapyroxad in vitro. The EC50 values of total number of isolates tested were ranged from 0.82 to 5.92 mu gml(-1). The ranges of EC50 values for the isolates varied between the localities where the isolates originated from and also the year of isolation. The mean EC50 values in the group of isolates obtained in 2013 were 1.95 mu gml(-1)+/- 0.81 (0.82 to 4.05 mu gml(-1)), while the EC50 values for those isolated in 2017 were ranged from 1.16 to 5.78 mu gml(-1) (mean=3.24 mu gml(-1)+/- 1.38). The efficacy trials were conducted during 2017 and 2018 in a commercial raspberry field at two locations in western part of Serbia. Applied in both concentration rates 0.02 and 0.03% of the formulated product (0.006 and 0.009% of a.i.), fluxapyroxad showed a very high efficacy in spur blight control in practical condition