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

Summary

The impact of a cultivar mixture within the rows including the cvs Melrouge (low susceptibility to scab) and Pitchounette (Rvi6 resistant) was assessed during 2008e2009 in an organic apple orchard located in Rhône Valley (Drôme, France), on three important pests and diseases: scab, powdery mildew and rosy apple aphid. In this area, the resistance of Rvi6 gene was effective since the orchard plantation in 2004. The impact of the cultivar mixture was assessed 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 scab incidence on leaves and fruits; a significant effect on scab severity was observed in 2009 for the cultivar mixture plus sanitation practices. Our data confirmed the different susceptibility levels of the two cultivars for powdery mildew. Against powdery mildew, a favourable effect of cultivar mixture, at the condition it is associated with sanitation, was observed in case of a moderate level of the disease (2008). For rosy apple aphid, a favourable effect of cultivar mixture was observed on Melrouge in 2008 when Pitchounette has a good resistance level. In the context of organic production, the impact of the cultivar mixture seemed favourable for the control of the three pests and diseases.