This edition has been prepared by B. H. McGauley and C. S. Kirby. Feb. 24, 2010, Guelph, Ont. During the late spring, summer, and early fall, it continually produces spores which cause new infections. Ontario M7A 1N8. 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 can be easily controlled through proper spraying of fungicides at the proper time of the year. 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. 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 … Of those, apple scab tissue from seven locations was found to be QoI-resistant in tests at Michigan State University. Full resistance to the strobilurin fungicide, Flint, has yet to be detected in Nova Scotia. 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 is caused by a fungus called Venturia inaequalis. QoI (quinone outside inhibitors) is a group of fungicides that include strobilurins. (3) sprays throughout the early growing season are necessary for season-long control. 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. Timing is crucial for control of Apple Scab. The disease is caused by the fungus Venturia Inaequalis. The disease is … 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. Apple Scab. Secondary scab lesions on leaves Scab lesions on leaves (image 1) Scab lesions on leaves (image 2) Scab lesions on fruits Common Pests of Trees in Ontario is a revised edition of Common Pests of Ornamental Trees and Shrubs, first printed in l975. 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. Apple scab lesion in the early stage of development. Absolutely! 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