Mcshay Apple

Apple scab caused by Venturia inaequalis (Cke.) Wint., is the most serious disease affecting apples. Growing cultivars resistant to apple scab eliminates the need for control of this fungal disease. Apple scab is not the only disease that can hamper apple production in Ontario. Powdery mildew incited by Podosphaera leucotricha (Ell. & Ev.) Salm, and the bacterial disease, fire blight incited by Erwinia amylovora (Burr.) are also of major concern.

Cultivars with resistance to the major early season diseases (apple scab, fire blight, powdery mildew, cedar apple rust) are now under development and a few which are moderately or highly resistant to these diseases have been released. However, combining resistance to several diseases in a new apple cultivar, as well as maintaining desirable fruit characteristics, has been a formidable task. The level of reported disease resistance and the quality of the fruit produced for disease resistant cultivars in outlined in Table 2.

Resistance to other, less prevalent diseases, has not been included in disease resistance breeding programs. Susceptibility of the cultivars listed here to such problems as black rot, sooty blotch, fly speck, quince rust and other diseases remains largely undetermined. Such diseases might limit the adaptablility of otherwise disease resistant cultivars in some locations if no fungicide sprays are applied.

Before a large planting of disease resistant apples is attempted, disease resistance, fruit quality, and most importantly, market acceptability should be evaluated under a grower's own set of circumstances. Because of the wide range of growing conditions in Ontario apple districts, the best way to evaluate these cultivars is to establish your own small planting including those cultivars of interest.