DISEASES
Anthracnose (Leaf and Twig Blight): The most important sycamore leaf disease is anthracnose caused by the fungus Gnomonia platani (Discula platani). This disease may appear as four distinct phases:
Twig Blight: Occurs in the spring before leaf emergence, killing tips of small, 1-year-old twigs.
Bud Blight: Occurs in April and May; the expanding buds die because of the girdling action of the canker on the branch.
Shoot Blight: New shoots and immature leaves on infected branches suddenly die.
Leaf Blight: The most characteristic symptom is a crinkling and browning of the leaves. Entire leaves may be killed and then fall. These symptoms are very similar to those caused by late spring frost injury.
This disease is favored by cool, wet weather (temperatures under 60 ° F during budbreak and the first few weeks of growth). A severely infected tree may be defoliated several times in a single season. Small twigs and branches may be affected, and cankers may girdle and eventually kill the branch. This will result in the production of many small shoots from the area just below the girdled portion of the branch, giving that part of the tree a bushy appearance. Spores are spread by rain and wind to healthy leaves, buds and twigs. The fungus survives the winter on fallen leaves and twigs.
Prevention and Treatment: Fallen leaves and twigs should be raked up and destroyed. Diseased branches should be pruned out and destroyed. This will limit the number of spores being produced by the fungus to start new infections. Care should be taken to sterilize pruning shears in rubbing alcohol or other disinfectant after pruning each infected branch. Adequate fertilizer and water should be applied to maintain the vigor of the tree. The cultivars ‘Bloodgood,’ ‘Columbia’ and ‘Liberty’ are moderately resistant to anthracnose. Spring applications of bordeaux mixture, copper, chlorothalonil or thiophanate-methyl fungicides may control the disease. Read and follow all directions on the label.
Powdery Mildew: The fungus Microsphaera alni is common on plants growing in shady areas. Young leaves and twigs are covered with a thin layer or irregular patches of grayish white powdery material. Infected leaves are distorted, and many may turn yellow and drop off. New growth is often stunted. In late summer, tiny black dots (spore-producing bodies) are scattered over the white patches like ground pepper.
Prevention and Treatment: Control is usually not warranted. Several fungicides may be applied, such as myclobutanil, triforine or triadimefon. Read and follow all directions on the label.
Summer Leaf Scorch: During hot weather, usually in July or August, leaves turn brown around the edges and between the veins. Sometimes the whole leaf dies. Many leaves may drop during late summer. This problem is most severe on the youngest branches. This problem may be mistaken for damage caused by anthracnose or lacebugs. However, the brown areas caused by anthracnose cross over the veins and often cover the entire leaf. Lacebugs leave brown droplets of excrement on the lower surfaces of the leaves. Physiological leaf scorch is caused by excessive evaporation of moisture from the leaves. If the roots cannot absorb and transport water fast enough to replenish this loss, the leaves turn brown and wither. The bacterial leaf scorch pathogen, Xylella fastidiosa, can also cause scorching of leaves by plugging up the water-conducting tissues.
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