Fungicide resistance in Botrytis cinerea in raspberry and strawberry in Norway

Abstract: Due to suspicion of reduced efficacy of fungicides against grey mould (Botrytis spp.), six to ten isolates of the fungus were collected from each of five raspberry and seven strawberry fields (open field production systems). Germination and hyphal growth were recorded on agar media amended with the various fungicides at different concentrations. The isolates were characterized as sensitive, less sensitive, moderately resistant or resistant. In raspberry, approximately 60% of the isolates were resistant against boscalid, pyraclostrobin or fenhexamid, and in four of the five raspberry fields, more than 50% of the isolates were resistant against all three fungicides. Only 7.5% of the isolates were resistant against pyrimethanil and none against iprodione or fludioxonil, however, 24% was moderately resistant to iprodione and 5.7% to fludioxonil. The situation in strawberry was very similar; 82, 68 and 57% of the isolates were resistant to fenhexamid, boscalid and pyraclostrobin, respectively. For pyrimethanil, 30 and 25% of the isolates were resistant and moderately resistant, respectively, and for iprodione, 17 and 52% of the isolates were resistant and moderately resistant, respectively. None of the isolates was characterized as resistant against fludioxonil, but 5% was moderately resistant. Of all isolates tested in strawberry, 8, 23, 25 and 10% were resistant against 2, 3, 4 and 5 fungicide groups, respectively. It may be concluded that there was a high degree of fungicide resistance in the investigated raspberry and strawberry plantings, and multiresistant strains occurred frequently.