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Apple Scab, Crabapple Tree Disease

Q. My crabapple trees (and those of many of my neighbors) have suffered from a disfiguring disease for several years. The trees bloom well in spring, but soon afterward, the leaves develop spots, turn brown, and drop off the tree by midsummer. What can we do?

A. Apple scab is a fungal disease that attacks non-resistant crabapple and apple trees. The infection first shows up on the foliage as darkened, sunken spots. The leaves will often turn yellow and then brown, dry up, and fall off the tree. Developing fruit can be scarred as well. The fungus overwinters on any fruit or foliage that remains on the property. Cool, wet spring conditions reactivate the fungus, and it can once again attack the trees.

All fallen leaves and fruit should be removed from your property immediately. Avoid overhead watering since that spreads the fungus. Some gardeners replace their disease-prone crabapples with resistant varieties to avoid annually spraying their crabapples with fungicide. Non-resistant crabapples must be sprayed as soon as their leaves begin to unfurl. Repeat applications are necessary every 10 to 12 days until midsummer.