Growing a successful apple orchard in the Carolinas requires lots of sunlight, soil with a pH between 5.8 and 6.5, and a disease-resistant variety. Apples are susceptible to many diseases, particularly during the summer. Clemson University Extension recommends the Liberty or Freedom varieties because they are resistant to several commonly found apple tree diseases. Using good sanitation practices, such as removing dead or diseased wood, debris and apples, will help keep many diseases at bay.
Trees infected with the apple scab fungus can suffer from defoliation and malformed fruit. Early symptoms include feathery, velvety brown marks on both sides of the leaves. The leaves can then become distorted, curled or dwarfed, and eventually they drop. Apple scab lesions on the fruit are brown and cork-like, and the fruit may crack or become deformed. According to Kearneysville Tree Fruit Research and Education Center, apple scab can cause 70 percent or higher losses in areas with moist, cool spring weather.
Powdery mildew is a fungus that overwinters in apple trees' terminal buds. It affects the tree's leaves, blossoms, fruit and twigs. Symptoms include small white or gray fuzzy patches that spread and eventually cover large areas of the tree. Infected apple blossoms turn brown, shrivel and die. According to Oregon State University Extension, infected fruits develop a network of lines (called "russeting") on the diseased area.
Fire blight is a bacterial disease that can severely damage or kill apple trees. The first symptom appears on apple blossoms, with the flowers appearing water-soaked, then wilting and turning brown. Infected twigs will wilt at the tips. The fruits initially appear water-soaked or oily, covered with a milk-like ooze. The apples will shrivel but remain on the branches. As the bacteria moves into the larger parts of the tree, the tissue will appear blighted and also will ooze the milk-like liquid.
Cedar Apple Rust
Cedar apple rust is a fungal disease that affects most apple cultivars in the Carolinas, except Delicious, which is practically immune. Symptoms of cedar apple rust include glistening yellow-orange lesions on the trees' leaves that later produce tufts of spores on the lower sides. Infected stems swell slightly and may lead to abscesses on the fruit. According to North Carolina State University, apple trees become infected when grown in close proximity to the Eastern red cedar, which also hosts the fungus.
The fungal black rot first appears on the apple leaves as a purple speck. The speck grows and develops a tan or brown center, and eventually the leaf drops. Infected limbs may have slightly sunken, red-brown cankers. Black rot appears on fruit as tiny purple or red spots that grow and turn brown or black. The entire fruit will submit to the rot, becoming mummified and generally staying on the tree. Black rot is often seen in poorly pruned trees with dead wood.