Impact of a cultivar mixture on scab, powdery mildew and rosy aphid in an organic apple orchard

Abstract: The impact of a cultivar mixture within the rows including the cvs Melrouge (lowsusceptibility to scab) and Pitchounette (Rvi6 resistant) was assessed during 2008-2009 in anorganic apple orchard located in Rhône Valley (Drôme, France), on three important pests anddiseases: scab, powdery mildew and rosy aphid. In this region, the resistance of Rvi6 gene waseffective since the orchard plantation in 2004. The impact of the cultivar mixture was evaluatedper se, but also associated with sanitation practices to decrease the primary inoculum of scab andmildew, and compared to disease development on pure stands of Melrouge. The cultivar mixtureshowed a good efficiency to decrease the development of scab on leaves and fruits. An importanteffect on the number of scab lesions per shoot was observed in 2009 for the cultivar mixture plussanitation practices. Our data confirmed the different susceptibility of the 2 cultivars for powderymildew. A mixture effect of cultivars was observed in 2008 against powdery mildew. No effectof sanitation practices was observed. For rosy aphid, a favourable effect of cultivar mixture wasobserved in 2008.