DEVELOPMENT OF RESISTANCE TO DICARBOXIMID ES IN INTEGRATED CONTROL OFBOTRYOTINIA-FUCKELIANA (DEBARY) WHETZEL

The development of resistance of Botryotinia fuckeliana to dicarboximi des was evaluated in a vineyard in Walenstadt which has been managed f ollowing the Swiss guidelines for Integrated Pest Management (IPM). Di carboximides have been scarcely used; in total, they were only applied seven times from their commercial introduction in 1977 to the start o f the experiments in 1989. In the following 3 years, they were applied once in 1989 and twice in 1991, the vineyard was not sprayed in 1990. A single dicarboximide spray at veraison in 1989 caused an increase o f the proportion of resistant isolates from less-than-or-equal-to 25 % at the beginning of the experiment to 100 % at harvest. Between the s ampling at harvest in autumn 1989 and the following spring, the propor tion of resistant isolates was reduced to less-than-or-equal-to 20 %. The proportion of resistant isolates on mature grape berries was only 5 % in 1990. In spring 1991, the proportion of resistant isolates was less-than-or-equal-to 15 %. While the proportion of resistant isolates increased to 100 % by two applications of dicarboximides the proporti on of resistant strains in the untreated, neighboured part of the plot remained at 15 %. The resensibilization has no sustainable effect as a single spray caused the increase of the proportion of resistant isol ates to 100 %. Despite IPM and a reduced number of sprays, the build u p of a resistant subpopulation could not be prevented.