Sensitivity of Erysiphe necator to quinoxyfen in Italian vineyards during 2009-2013

Introduction: Grapevine powdery mildew, caused by Erysiphe necator (Schw.), is present every year in Italy, and can drastically reduce yield and quality of grapes leading to important economic losses. Control of this obligate biotroph is mainly based on the use of fungicides. Quinoxyfen belongs to the Azanapthalene group of fungicides and is a preventive fungicide used to control the powdery mildew diseases of wheat, barley and grapes: it is a potent inhibitor of appressorium formation of these fungi [1]. Quinoxyfen is categorized as at medium risk of resistance development by FRAC. Field isolates of E. necator with a reduced sensitivity to quinoxyfen were first detected in 2003 [2] although under practical field use conditions the performance of quinoxyfen remains effective. In wheat Blumeria graminis isolates with significantly reduced sensitivity to quinoxyfen have also been detected in 2001 [3, 4]. The aim of this study was to evaluate the sensitivity to quinoxyfen of E. necator isolates collected from Italian vineyards characterized by different histories of quinoxyfen use...............................................