Is low efficacy of fungicides always a consequence of fungicide resistance development in pathogen populations?

Efficacy of four fungicides with different modes of action (vinclozolin, pyrimethanil, benomyl and fenhexamid) in control of B. cinerea in raspberry, was investigated in the paper. The trials were conducted at two localities in commercial raspberry plantations. In the case of unsatisfactory fungicide efficacy, qualitative and/or quantitative test of the susceptibility of the isolates to particular fungicide was performed, to determine whether the low efficacy is a consequence of resistance development in the pathogen population. At both localities, pyrimethanil and fenhexamid demonstrated the highest efficacy (73.2-89.6%), while the efficacy of vinclozolin was statistically significantly lower (48.7-63.4%) at both localities. However, qualitative and quantitative test of susceptibility to vinclozolin showed that all the isolates were susceptible to vinclozolin and that the reason for unsatisfactory efficacy should be primarily sought in inadequate fungicide application.