Fungi cause most tree leaf diseases, but bacteria and viruses also cause some of the diseases. A causal agent may affect only one species of tree or many species of trees. Usually symptoms of a particular disease are the same on all affected species, but in some cases, the symptoms may vary from species to species.
Many tree leaf diseases can be prevented by planting a tree in the right location, with the proper amount of sun or shade, irrigation and drainage. Plant trees far apart to allow the foliage to dry quickly after dew, fog or rain. Prune and destroy infected plant material and diseased or dead plant debris around trees to prevent the spread of diseases.
Leaf spots are the most common disease on tree foliage. Fungi or bacteria that cause leaf spots are spread by air or water and need moisture to grow. Leaf spots normally occur in late summer to early fall and do not cause much damage. Leaf spots that begin in early spring may cause premature dropping of foliage. If this happens for more than two consecutive seasons, the affected tree may lose vigor or even die. Apply fungicides approved for the causal agent on the host plant according to the manufacturer's directions to prevent or control some leaf spots.
Symptoms of leaf spots include circular, oval or irregular spots or patches of discolored or dead leaf tissue. The areas may be light green, yellow, tan, reddish-brown, purplish-brown, brown or black. Some leaf spots resemble targets with halos or concentric rings. Others are raised areas that look like blisters. The dead leaf tissue may fall out of some infected foliage, leaving shot holes. Severely infected leaves may turn entirely yellow or brown and drop off prematurely.
Anthracnose is a fungal disease that causes leaf spots and can spread into the woody tissue of affected trees. It occurs during cool, wet weather in late spring or early summer. Initially, irregular dead areas of leaf tissue appear on the edges and along the veins of infected leaves. The disease may extend across the entire leaf and into shoots or small twigs.
Anthracnose can cause early leaf drop in infected trees. Repeated defoliation can cause the affected tree to weaken or die. Use a fungicide approved for anthracnose on the host plant according to the manufacturer's instructions to prevent and control the disease.
Powdery mildew can occur on the foliage of almost every species of tree during humid weather. Patches of white fungal growth appear on infected leaves and may spread to buds, flowers and stems. If the disease is severe, use a fungicide for powdery mildew on the host plant at the rate recommended by the manufacturer.
Sooty mold is a fungus that grows on honeydew secreted by sucking insects, such as aphids. It can be washed off the foliage with a strong spray of water. Use an insecticide for camellias at the rate recommended by the manufacturer to get rid of the insects.