Apple scab is a fungal disease caused by the fungus venturia inaequalis. It can affect the leaves, fruit, and twigs. While most common in apple trees, both pear and hawthorn are also frequently infected by the fungus. Outbreaks will be most severe following particularly wet and cool spring conditions. The disease infects the leaves, twigs and fruit.
Signs of Apple Scab
Infection is commonly evidenced first by brownish green spots on the leaves or fruit. As the infection progresses, the spots on the fruit become darker and more prominent and take on a somewhat fuzzy texture. When infection is severe, leaves will turn yellow and drop off. Fruit will become deformed and/or drop off prior to ripening.
Apple Scab Treatment
Arborjet recommends a trunk injection with a systemic fungicide, either PHOSPHO-jet or Alamo. The best results will be achieved when PHOSPHO-jet or Alamo are applied prior to infection. Applying PHOSPHO-jet or Alamo in the fall will minimize or prevent infection the following spring. If applying in the spring, it should be applied as early in the spring as possible. Application will be easiest, and fastest, when tree is actively transpiring.