Sensitivity of <i>Neonectria ditissima</i> to carbendazim fungicide in New Zealand

Abstract

Carbendazim can be used by New Zealand pipfruit growers for control of European canker caused by Neonectria ditissima A total of 162 N ditissima isolates were tested for carbendazim sensitivity using a mycelial growth assay on amended malt extract agar plates at concentrations from 02 mg/litre Generally isolates ceased growth at 2 mg/ litre carbendazim with 65 isolates ceasing growth at 1 mg/litre The EC₅₀ values calculated for 19 isolates ranged from 051 to 138 mg/litre The data suggested that isolates ranged from sensitive (EC₅₀<1 mg/litre) to having intermediate resistance (EC₅₀110 mg/litre carbendazim) based on comparison with other agarbased studies Resistance in other fungi has been reported at carbendazim concentrations of >100 mg/litre The isolates tested were mostly sensitive to carbendazim but some showed a shift towards intermediate resistance Mycelial growth tests at 2 mg/litre may be a useful tool to screen single spore isolates quickly for potential carbendazim resistance