Apple scab can be easily controlled through proper spraying of fungicides at the proper time of the year. This edition has been prepared by B. H. McGauley and C. S. Kirby. Apple Scab. QoI resistant apple scab confirmed in Ontario A recent sampling program of scab-infected apple leaves from orchards across Ontario has revealed the presence of QoI-resistant apple scab. Of those, apple scab tissue from seven locations was found to be QoI-resistant in tests at Michigan State University. Apple Scab is caused by a fungus called Venturia inaequalis. Feb. 24, 2010, Guelph, Ont. Apple scab is a common fungal infection and is problematic for apple growers everywhere, although it can be harder to control in coastal areas. Apple scab lesion in the early stage of development. (3) sprays throughout the early growing season are necessary for season-long control. Timing is crucial for control of Apple Scab. However, there are orchards where the scab population has started to shift towards resistance to this fungicide. for scab control in the mid 1990’s. The disease is … Infections usually develop first on the undersides of leaves. Generally, you’ll first notice it in early spring, when rains, wind, and cool temperatures spread the fungal spores. A young apple grower, Laura Sagar, has adopted new cultural control (these include non-chemical means of reducing pest pressure, such as removing infected leaves or using disease resistant varieties) strategies to reduce the risk of scab, and weather-based disease models to forecast the risk of scab … Ontario M7A 1N8. Apple scab generally does not kill the trees but it can cause defoliation, which will weaken the tree and influence its survival during winter conditions. Apple Scab occurs on the leaves, petioles, blossoms and fruit. Secondary scab lesions on leaves Scab lesions on leaves (image 1) Scab lesions on leaves (image 2) Scab lesions on fruits Full resistance to the strobilurin fungicide, Flint, has yet to be detected in Nova Scotia. Common Pests of Trees in Ontario is a revised edition of Common Pests of Ornamental Trees and Shrubs, first printed in l975. The disease is caused by the fungus Venturia Inaequalis. Apple Scab occurs in most areas of the world where apples are grown, it is one of the most serious diseases of ornamental crabapple and fruit trees. Apple scab is caused by a fungus, Venturia inaequalis, and is a serious disease of apple and crabapple (genus Malus) trees that spreads quickly and easily. During the late spring, summer, and early fall, it continually produces spores which cause new infections. The fungus over winters in fallen leaves on the ground and in spring the spores become active again and infect the new growth on the tree. 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