Tulip trees, Liriodendron tulipifera, are members of the magnolia family, and like the magnolia, produce showy flowers. Also known as yellow poplars, these fast-growing shade trees average a height of 80 to 100 feet. Tulip trees are ideal ornamental shade trees because of their resistance to pest and disease damage.
Wounded tree branches and trunks create prime locations for fungus and bacteria to grow. Growing slowly during the dormant season, cankers appear as sunken or swollen areas on branches and trunks. Nectria canker and Fusarium canker are two of the most common cankers in tulip trees. Fungicides are not helpful in treating cankers. The best management strategy is stress avoidance. Cankers grow quickly in trees stressed due to drought and poor soil. Sterilizing pruning tools, annual fertilizing and adequate soil moisture keep the tulip tree healthy enough to prevent widespread damage from canker fungus.
Leaf spot is a fungus that creates round and oval-shaped spots on tulip tree leaves. These spots while unsightly are not usually harmful to the tree. If leaf spot begins early in the growing season, it may begin to weaken the tree thus making it susceptible to other pests and diseases. Proper fertilization and pruning helps the tree fight off small infestations of leaf spot. If the tree is stressed, fungicide sprays may be used to reduce secondary infections resulting from other fungus.
In late summer and early fall, a dusty white fungus, called powdery mildew, grows on the leaves of the tulip tree. Beginning as small white spots, the fungus expands into a continuous mat of mildew coating the leaf. Since it usually appears at the end of the growing season, powdery mildew does not seriously harm the tree. If the tree is stressed, apply a fungicide as soon as the white spots are noticed. Repeat applications will be necessary.
A black fungus, called sooty mold, coating tulip tree leaves signifies a much more serious problem. Sooty mold grows on honeydew which is excreted by aphids or scale insects who are feeding on tree sap. Sooty mold, if left unchecked may cause early leaf drop. Control sooty mold by eliminating the insects which secrete honeydew. Pesticides and horticultural soap effectively kill these pests. Once the honeydew dries, the sooty mold will also disappear.
Verticillium wilt, a fungus that lives in the soil, enters the tree through wounds in the roots. The fungus produces a toxin that causes damage to the tree’s veins. Once it spreads throughout the tree, the restricted flow of water and nutrients causes the leaves to yellow and wilt. Eventually the whole branch will die and if left unchecked the entire tree will die. Symptoms appear most often in July and August. The fungus can survive in the soil for more than 10 years without a host. There is no chemical cure for verticillium wilt. Immediately remove weak or diseased branches. Using a high potassium/low nitrogen fertilizer and watering well may decrease the spread of the infection.
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