KATAN, T., Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, Bet Dagan, 50 250, Israel
ELAD, Y., Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, Bet Dagan, 50 250, Israel
YUNIS, H., Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, Bet Dagan, 50 250, Israel

Based on the ‘negative cross‐resistance’ phenomenon between N‐phenylcarbamates and benzimidazole fungicides, the fungicidal mixture of carbendazim + diethofencarb (MBC + NPC) was introduced, to control Botrytis cinerea phenotypes which are either sensitive to benzimidazoles and resistant to NPC (wild‐type: BenS NPCR). or resistant to benzimidazoles and sensitive to NPC(BenR NPCS). At one out of four sites where the MBC + NPC mixture was used in commercial cucumber greenhouses, grey mould control failed and a new phenotype of B. cinerea was found. The new phenotype was resistant to benzimidazoles, as was 100% of the population screened in the four sites, but retained resistance to NPC. Accordingly, the new phenotype was designated BenR NPCR. It was pathogenic on cucumber seedlings. Copyright © 1989, Wiley Blackwell. All rights reserved