Influence of fungicide spray schedules on the sensitivity of Cercospora beticola to the sterol demethylation-inhibiting fungicide flutriafol

A field experiment was conducted over a three-year period (1997-1999) to st udy the efficacy of several fungicide spray-schedules and their effects on the sensitivity of Cercospora beticola populations to the DMI fungicide flu triafol. Spray applications of flutriafol, either alone at the recommended dose, or at a reduced dose in mixtures with maneb, or in alternation with t ank mixed fentin-acetate and maneb, were included in the spray programs. Ap plications of flutriafol at the recommended dose showed a significantly gre ater control efficacy in comparison with the other treatments, while applic ations of flutriafol alternated with tank mixed fentin-acetate and maneb sh owed lower efficacy in comparison with the remaining flutriafol treatments. Fungal populations from plots continuously treated with flutriafol, either alone at the full dose or at reduced dose with maneb, had lower sensitivit y to flutriafol in comparison with populations from plots treated alternati vely with flutriafol and tank mixed fentin-acetate and maneb. Repeated appl ications of flutriafol, at full or reduced doses, favoured the selection of highly resistant strains. Since applications of flutriafol in alternation with tank mixed fentin-acetate and maneb do not maintain a high level of di sease control, the only available antiresistance strategy would be the rest riction of the number of flutriafol treatments, by applying them only when environmental conditions are favourable for disease development and by usin g alternative fungicides during the rest of the growing season. (C) 2001 El sevier Science Ltd. All rights reserved.