Negative cross resistance between benzimidazole and N-phenylcarbamate fungicides and control of Botrytis cinerea on grapes

Isolates of Botrytis cinerea resistant to benzimidazoles (Ben^R), dicarboximides (Dic^R), or both (Ben^R Dic^R) were found on table grapes in vineyards in Israel. In vineyards treated for one or two seasons with benomyl and dicarboximides, 41% of the isolates were benomyl-resistant, 18% were dicarboximide-resistant and 21 % were resistant to both fungicides. The frequency of resistant strains was very low in non-treated vineyards. Negatively correlated cross resistance (NCCR) was manifested by 46 Ben^R isolates which were sensitive to isopropyl N -(3,4-diethoxyphenyl) carbamate (NPC) and 73 benomyl-sensitive (Ben^s) isolates which were insensitive to NPC; NCCR was not influenced by sensitivity to dicarboximides. A mixture of Ben^s Dic^R plus Ben^R Dic^s isolates, inoculated on rose petals, was inhibited by mixtures of benzimidazoles plus NPC but not by benomyl, NPC or iprodione alone. Grey mould, incited on maturing grape berries by a vineyard population composed of Ben^s and Ben^R strains, was not controlled by benomyl, while the mixture of NPC plus carbendazim was effective.