Apple Scab is one of the most common diseases that attack apple trees. Apple Scab is caused by a fungus (Venturia inaequalis) which is most prevalent and aggressive in geographical areas where spring weather is mild (about 60 to 70 degrees F) and conditions are wet.
Apple Scab initially appears as small brown spots on the undersides of leaves, and then spreading to the top of the leaf and eventually to the fruit itself. On the fruit it appears as light brown spots, about ¼ to ½ inch in diameter. The brown spots feel rough to the touch. When a tree is attacked by Apple Scab, the fruit is often malformed and cracked and can drop prematurely. In cases of severe infestations, a tree can become totally defoliated.
The Apple Scab fungus overwinters in fallen leaves on the ground and then re-infects that tree in the spring as it is moved by the wind. If it lands on leaves that are wet it will begin to spread spores, which infect the leaf and fruit. In most cases, even infected fruit is still edible.
To control Apple Scab, in the fall remove and destroy any fallen leaves that are under the tree. In the spring, spray the tree with Captan Fungicide. The tree should be sprayed as soon as the leaves emerge on the tree and again once the leaves are fully developed. A further spraying can be done when the fruit has begun to develop. To increase the effectiveness of the Captan Fungicide, apply it with Nature's Own Spray Helper, which increases the rate of bonding and penetration of the fungicide into the tree’s foliage.
If spraying is not an option, apply Agri-Fos with Pentra-Bark directly onto the tree’s trunk. For maximum benefit, the ArborFos Injectible Systemic Fungicide should be applied early in the spring.