The Q&A Archives: Apple Scab

Question: I use sulfur for scab. The instructions on the dormant oil spray say not to mix it with sulfur as it will kill the foliage. Any suggestions? What's the schedule?

Answer: Apple scab is a fungus that overwinters on dead leaves and fallen fruit, so first order of business is to keep debris cleaned up in the garden. Some cultivars are resistant to scab, including Akane, Chehalis, Liberty and Jonagold, so grow those varietiesif you can. The key to successfully controlling scab is to apply fungicides early and thoroughly to protect new growth. Use a wettable sulfur solution or a Bordeaux (lime-sulfur) spray as soon as the cluster buds develop, again at pre-pink, pink, and after petals fall. Avoid spraying when trees are in full bloom. Dormant oil sprays help suffocate overwintering scale insects and insect eggs and should be applied while trees are dormant, on a dry day when the temperature is above 40F degrees. Apply before the buds begin to swell. Fruit trees certainly require a great deal of care to produce disease-free fruit! There are publications about fruit tree spraying, available at your local WSU Cooperative Extension Office at 222 N Havana, Spokane, WA 99202. Or phone (509) 533-2048.

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