Studies on the survival and infective ability of dicarboximide‐resistant strains of Botrytis cinerea

SUMMARY Few dicarboximide‐resistant strains of Botrytis cinerea produce macroconidia either on culture media or on natural substrates, although, the viability of such conidia was similar to those of sensitive strains. The ability of dicarboximide‐resistant strains to infect strawberries was similar to that of sensitive strains and most of the resistant strains competed successfully with sensitive strains when inoculated in equal numbers onto detached strawberries and onto flowers of field‐grown plants, especially after treatment with dicarboximide fungicides. All resistant strains tested survived for at least 9 months on inoculated strawberry leaf litter although their incidence was ‘diluted’ by wild type sensitive strains. Sporulation and dispersal of resistant strains from the litter was very limited resulting in a low incidence of fruit infection even after treatment with dicarboximides. Consequently, there was no significant increase of resistant strains in the plantation and control of infection was maintained with iprodione and dichlofluanid. Poor sporulation of dicarboximide‐resistant strains of B. cinerea is considered to be the single most important factor in limiting their development in the field.