Effects of DMI and strobilurin fungicide combinations on scab and powdery mildew incidence in apple production: a preliminary study

Rules and several tools for fungal disease management are well-defi ned and most of them are successfully implemented for environmentally friendly productions systems in apple (e.g. Zalom, 1993). Disease management practices in integrated apple production differ markedly from those in conventional production. Synthetic products are restricted in integrated apple production. Growers can use only those fungicides which are sorted into ’green’ and ’yellow’ list of active ingredients by the international integrated fruit production guidelines, while many synthetic pesticides can be used in conventional apple production. In integrated apple orchards the most often used systemic fungicides are DMIs and strobilurins against the key diseases such as apple scab and powdery mildew (e.g. Koller et al., 1997; Holb et al., 2005, 2009). The extensive use of DMI and strobilurin fungicides resulted in fungicide sensitivity reduction or fungicide resistance in apple scab and powdery mildew (e.g., Délye et al., 1997; Koller et al., 1997; Hollomon & Wheeler, 2002; Jobin & Carisse, 2007). Several resistance management strategies were developed to avoid apple scab resistance to DMI fungicides but an overall solution is still under development. One of the most essential diffi culties is cross-resistance occurring among DMI fungicides, which makes more diffi cult to plan an effective disease management strategy (e.g. Koller et al., 1997). Various combinations of DMI and stobilurin fungicides in a season-long disease management programme may contribute to a successful fungicide resistance strategy for both fungicide groups in the control of apple scab and apple powdery mildew. The aim of our study was to evaluate the effectiveness of three DMI and strobilurion fungicide combinations in a season-long disease management programme against apple scab and powdery mildew. The study was performed in two integrated apple orchards on a scab susceptible apple cultivar Jonagold.