Apple scab is the most common disease of Apples, it caused by the fungus Venturia inaequalis.
It infects both leaves and fruit.
Ideal conditions for scab spreading are wet, cool weather that generally occurs in spring at 13-23 degrees Celsius.
Chemical control:
Final-T (Thiophanate methyl 85% WP)
65 Grams / 100 Liters of water.