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Fruit Varieties Journal
(Fruit Var J)

American Pomological Society

Volume 48 Number 1 Article 8 Pages: 35-35
Year 1994 Month 1
Title: Disease Management of Scab-Resistant Cultivars
Authors: L.P. Berkett, J.F. Costante, K.N. Bower, J. Clements and D. Schmitt
Citation
Abstract:
While 'disease resistant cultivars' are immune to apple scab, they may be affected by other fungal diseases such as cedar apple rust, powdery mildew, and frog-eye leaf spot that affect the foliage and/or fruit. Apple growers need to know what diseases are poten tial problems on the cultivars; they also need information on how to effec tively manage these diseases. The ob jective of this study was to determine the incidence of foliar and fruit diseases on scab-resistant trees treated with minimal fungicides compared to nontreated trees. The investigation was conducted in an orchard containing 8 scab-resistant cultivars and 2 scabsusceptible cultivars. Each cultivar represented an individual block con taining 5-13 trees. Within each cultivar block, the treatments (fungicide treat ment versus no fungicide treatment) were randomly assigned to the trees. In 1988 and 1989, the fungicide treatment consisted of 6 applications of benomyl and mancozeo applied be tween the 'pink' phenological stage to approximately 2-3 weeks after petal fall. In 1990 and 1991, myclobutanil plus captan were applied at the pink and petal fall phenological stages. Each year, disease incidence was assessed on cluster and terminal foliage. In 1990 and 1991, fruit were also evalu ated. The cultivars exhibited a range of susceptibility to cedar apple rust. On those cultivars that were less sus ceptible to cedar apple rust, a 'frogeye leaf spot' was more prevalent. Fungicides did have a significant effect on incidence of cedar apple rust and leaf spotting. Percentages of non-treat ed fruit on which no disease symptoms or disorders were detected at harvest ranged from 523! on 'Nova Easygro' to 928! on 'Redfree' and 'Freedom' in 1990, and 50X on 'Freedom' to 992 on 'Liberty' in 1991.

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