Limited information of fungicide efficacy on cultivated mushrooms and resistance development potential
is available. Minor crop industries in general have a smaller arsenal of protectants to rely on and the
likelihood of resistance build-up is of greater concern. This study focused on Cladobotryum mycophilum's
sensitivity to carbendazim and prochloraz manganese following recent reports on decreased efficacy of
both fungicides. The median effective dose (ED50) values for carbendazim ranged between 0.02 mg/L and
4.31 mg/L with 60% of the South African isolates being moderately resistant. The highest resistance factor
for carbendazim was 215. Prochloraz manganese ED50 values varied from 0.00001 mg/L to 0.55 mg/L.
A significant difference in mean ED50 values for both fungicides tested was observed. Using cluster analysis,
no discrimination of isolates previously exposed and unexposed to prochloraz manganese was observed.
A wide range of differences in ED50 values indicated moderate resistance to carbendazim and high sensitivity
to prochloraz manganese among isolates under investigation. Discriminant analysis indicated significant
differences between clusters contributed by one or a few variables. This study provided evidence that
prochloraz manganese remains highly fungitoxic to C. mycophilum. However, prochloraz manganese is to
be used in a disease management strategy in combination with strict farm hygiene management strategies
to retain product efficacy and ensure crop protection.