Sensitivity of Stemphylium vesicarium to the most used fungicides to control pear brown spot in Italian orchards

In Italy one of the most important concerns for pear growers is the control of pear brown spot, caused by Stemphylium vesicarium, also present in some other European countries. Up-to-date knowledge of pathogen sensitivity to the most used fungicides is fundamental for the success of pear brown spot control, especially after the occurrence in northern Italy of a widespread resistance to dicarboximides in the early 1990s and recently of the first case of control failure caused by strobilurin resistance (2006). After several years of in vitro sensitivity monitoring we can state that the resistance to dicarboximides is stable or regressing while the resistance to strobilurins is increasing. In a very few cases a cross resistance between dicarboximides and fludioxonil was found whereas a good activity was recorded for dithiocarbamates, despite intense use for about 30 years. After some years of applications, S. vesicarium sensitivity to boscalid is still comparable to baseline values.