- The fungus Venturia inaequalis causes the black spot disease on apples. The disease is also referred to as apple scab. The pathogen in found in all the apple-growing regions around the world. Though somewhat similar in symptoms, apple black spot disease is not identical to pear black spot or rose black spot.
- The disease is characterized by the appearance of velvety textured, olive-green spots on the foliage. The spots get large and start to appear on the fruit. With age, the lesions assume a dark brown-to-black color and a scablike, warty appearance. The lesions on the fruit also develop cracks. Fruit that is infected late in the season shows tiny black, pinpointlike spots.
- Early infection of the tree damages the blossoms, causing blossom blight and fruit drop prior to ripening. Infected foliage also starts to drop, and infected fruit grows deformed and cracked. The damage to buds affects the coming year's harvest. The fungal spores persist in the fallen foliage under tree and reinfect the new foliage on tree during early spring.
- One of the best management practices is to remove all fallen leaves from under the tree to minimize chances of repeat infection from overwintering spores. Use preventative fungicides during pink, bloom and petal fall periods of tree. Spray tree again two weeks following petal fall. Recommended fungicides include products containing propiconazole or chlorothalonil. Choosing resistant apple varieties also minimize risk of infection. These include Liberty, Goldrush, Prima, Redfree and Enterprise.