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

Detection and characterization of fungicide resistant phenotypes of Botrytis cinerea in lettuce crops in Greece

The development of resistance to chemical control agents needs continuous monitoring in Botrytis cinerea. 790 isolates from lettuce and other vegetable crops were collected from six widely separated sites in Greece and tested for their sensitivity to 11 fungicides from nine unrelated chemical groups. 44 of the isolates exhibited multiple resistance to fenhexamid (hydroxyanilides), azoxystrobin and pyraclostrobin (QoI's), boscalid (SDHI's), cyprodinil and pyrimethanil (anilinopyrimidines), fludioxonil (phenylpyrroles), carbendazim (benzimidazoles) and iprodione (dicarboximides). Thirty per cent of such phenotypes were detected in an experimental glasshouse with lettuce crops, the third year after commencing fungicide applications. The average resistance factor (R-f) for mycelial growth to fenhexamid, pyraclostrobin, boscalid, cyprodinil and fludioxonil, was over 40, 1,000, 100, 700 and 50, respectively. Some strains with high resistance to anilinopyrimidines (14 %) or moderate to fludioxonil (7 %) were detected even in isolates collected from vegetable crops prior to commercial use of these fungicides in Greece. Isolates with fludioxonil moderate resistance and fenhexamid high resistance, were detected for the first time in Greece. The results suggested the high risk in chemical control of grey mould due to development of resistance to most fungicides with site-specific modes of action. Isolates with resistance to fluazinam (phenylpyridinamines) and to chlorothalonil (phthalonitriles) were not found. The inclusion of appropriate multi-site inhibitors like chlorothalonil in fungicide anti-resistance strategies was indispensable