Answer: Apple scab is a fungal disease. The fungus overwinters on dead leaves and fallen fruit, so first order of business is to keep debris cleaned up in the garden. 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. You should be able to purchase an inexpensive lime-sulfur spray to use on your tree rather than purchasing a brand name. Look in the fruit tree section of the garden center. It's really important that the timing is right - if you miss a spray, the fungus can take hold. Be sure to follow label directions and thoroughly spray all parts of the tree.
Best wishes with your apple tree!
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