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Guide to Crabapple Scab Disease and Control

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Gertens’s guide to crabapple scab disease and control will help you keep your trees healthy and scab-free. Read on to learn what causes the disease, how it spreads, and what you can do prevent your trees from getting sick.

Clean up leaf litter to prevent crab apple scab.

This plant disease is caused by a fungus (Venturia inaequalis) and can be a serious problem where spring weather can be humid. Mid-season leaves appear to turn yellow with velvety black spots 1/4 inch or more in diameter. Leaf drop usually follows by midsummer.
The fungus spreads in winter amongst the fallen leaves. In the spring, spore producing structures in dead leaves continuously discharge into the air and blow onto the new foliage and flowers. The cycle repeats until the wood becomes affected.

How to Control Crab Apple Scab

In the fall be sure to pick up all leaf litter around trees. In the spring as new foliage appears, spray tree with a fungicide like Bonide's Fruit Tree Spray as directed. Be sure to keep your trees healthy by fertilizing with a "Ross" root feeder.