Occurrence of Hyd R3 fenhexamid resistance among Botrytis isolates in Northern German soft fruit production

Strains of Botrytis cinerea with a high degree of resistance against the hydroxyanilide fungicide fenhexamid (resistance factor > 2000) were found in strawberry and raspberry fields of the two important Northern German berry fruit production areas around Vechta and south of the Lower Elbe river. The frequency of these Hyd R3 isolates in individual fields was variable, ranging from 0 to 100%. Affected raspberry orchards generally showed a higher proportion of Hyd R3 strains than Hyd R3-affected strawberry fields. It is suggested that repeated applications of fenhexamid over several successive years may have caused an enrichment of Hyd R3 strains in raspberries. Practical implications of these findings for regional soft fruit producers are discussed.