The OrganicA Project: Organic Disease Management in Orchards with ‘Newer’ Cultivars

Abstract: Although there is significant interest in organic apple production in the New England region of the USA, there are few certified organic orchards, in part, because of disease challenges associated with ‘McIntosh’, the predominant cultivar grown in the region. However, recent shifts in consumer preference for ‘newer’ cultivars have led to the planting of different apple cultivars which have different disease susceptibility. A long-term research project was initiated in 2006 to examine the opportunities and challenges of organic apple production within the two production systems growers are using to change to new cultivars: planting a new orchard with young trees purchased from a nursery and/or “top-grafting” an established, older orchard to new cultivars. The cultivars being studied in replicated plots in each orchard system are: ‘Zestar!’, ‘Ginger Gold’, ‘Honeycrisp’, ‘Macoun’, and ‘Liberty’, a scab-resistant cultivar. Both orchard systems are being managed with approved, organic practices and materials. Standard foliar disease assessments for apple scab, caused by Venturia inaequalis, and other diseases are being conducted to determine differences in disease incidence and severity among the cultivars. Based on initial foliar disease assessments during the establishment years of the orchards, ‘Honeycrisp’ appears more resistant to apple scab than the other scab-susceptible cultivars ‘Zestar!’, ‘Ginger Gold’, and ‘Macoun’, but appears more susceptible to cedar apple rust, caused by Gymnosporangium juniperi-virginianae, than ‘Liberty’ and ‘Zestar!’. ‘Macoun’ and ‘Zestar!’ exhibited a higher incidence of necrotic leaf spots than the other cultivars. This research is on-going and will document disease challenges and the economic costs, returns, and risks associated with these five cultivars being grown under organic production practices within the two orchard systems.