Scab is sometimes mistaken for other leaf spot diseases, but look closely. The dark spots on the leaves (which can also occur on fruit) are not dead tissue, but are small fungal colonies. Scab is common in rainy areas, but can also affect plants in overly moist conditions. Increase air circulation around the infected plant and reduce watering. Remove and destroy infected material for best results. Sulfur can be used to control scab in extreme situations.