Description: Leaf spots, or infections of leaves, are caused by a variety of fungi and some bacteria. Leafspots are seen more frequently in late summer as leaves begin to fall. Normally, autumn leaf spots do not affect the health of the tree and is the beginning of the natural process of decay.
Leaf spot fungi are spread by spores and carried by air currents or splashing rain. Trees in shady or crowded areas are more likely to be affected because moisture is retained longer there and infection requires moisture.
Symptoms: Oak leaf blister is a common leaf spot disease, occurring in March and early April. Water oak seems most susceptible, although any oak can get it. A blister-like spot is created on the leaves, causing them to distort. In more severe cases, leaves may drop. Continual leaf drop will cause stress to the tree inviting further insect and disease attacks.
Entomosporium leaf spot affects red-tip photinia and Indian hawthorne. Plants will shed leaves when the infection is severe and repeated infections will kill red-tips. Dark spots with purple margins are typical of this fungus.
Anthracnose is another leaf spot disease. Anthracnose is a disease that has decimated much of the native Dogwood populations in the forests of the United States. In mid-May through June, shortly after the leaves have expanded, spots and blotches of varying shapes and sizes appear on infected trees. These spots have a tan center and a purple or reddish margin. On the underside of the leaf, tiny black or brown spots may appear beneath the blotches. The flower ‘petals’ or bracts also show reddish or brownish blotches. In some cases, entire leaves are infected and die. The dried leaves remain on the stem throughout the fall and winter.
Powdery Mildew doesn’t produce leaf spots but leaves are left covered by a white, powdery film that can cause leaves to cup or distort. Many of the older varieties of Crape Myrtles are affected.
Bacterial leaf spots have brown or black water-soaked spots, sometimes with a yellow halo. As spots multiply the entire leaf may yellow, wither a drop. Cherry, plum and peach trees are particularly susceptible. Bacterial leaf spot thrives in warm, moist conditions, especially when plants are watered from overhead.
Action: Keep the soil under the trees clean and mulch the area to keep splashing rain from spreading the disease. Avoid over watering. Fungicides may be used on all leaf spots to prevent its spread. In some cases, proper pruning by thinning trees or shrubs will allow more air circulation thought the canopy and help prevent fungal growth.
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