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