Toxicity of mancozeb, chlorothalonil, captan, fluopyram, boscalid, and difenoconazole to Didymella applanata isolates from Serbia

Abstract

Field isolates of Didymella applanata, the causal agent of spur blight of raspberry, were evaluated in vitro for their sensitivity to mancozeb, chlorothalonil, captan, fluopyram, boscalid and difenoconazole. A total of 10 isolates, collected during 2013 at five localities in the major raspberry growing region in Serbia, and characterized as copper hydroxide, dithianon, and tebuconazole (sensitive), pyraclostrobin (sensitive or highly resistant) and fluazinam (sensitive or moderately resistant), were used in this study. The EC50 values for the isolates ranged from 1.33 to 2.88 mg L−1 for mancozeb, from 3.18 to 6.65 mg L−1 for chlorothalonil, from 15.75 to 24.69 mg L−1 for captan and from 1.80 to 8.20 mg L−1 for fluopyram. The narrowest range of EC50 values was recorded for difenoconazole (0.23–0.49 mg L−1), whereas the widest range was obtained for boscalid (4.49–49.25 mg L−1). The calculated resistance factors showed that all D. applanata isolates were sensitive to mancozeb, chlorothalonil, captan, and difenoconazole. Four isolates were moderately resistant to boscalid, while three of them were also moderately resistant to fluopyram. This finding of moderately resistant isolates to these SDHI fungicides indicates a possible cross-resistance which should be clarified in further investigations.