- Verticillium wilt is a soil-borne fungal disease that attacks trees growing in excessively moist soil. When verticillium wilt attacks, its initial presence is internal; infected trees exhibit discolored wood if they are cut open. Signs of infection include leaf drop without wilt, often beginning at the top or along one side of the tree, as well as twig and branch dieback. Pruning infected branches and keeping the soil free of excess moisture helps to slow verticillium wilt, but there is no treatment for it.
- Trees grown too close together may girdle one another's roots. Some trees, such as the maple, experience self-caused root girdling. Root girdling occurs when one root wraps around another and chokes it off, stopping it from transporting nutrients to the leaves and branches. Leaf loss from the crown of the tree indicates girdling. Removal of the strangling root is important for allowing the tree to recover, as root girdling contributes to the overall decline of the tree.
- Drought is a major problem for many trees. Leaves farthest from a limited or dwindling source of moisture are the first to show signs of damage, as it is more difficult for the tree to get water to the crown as opposed to the lower branches during times of drought. Nutrient deficiencies and a lack of proper sunlight also contribute to early leaf loss on the crowns of trees. Supply trees with water and fertilizer, and make sure they receive sunlight during the day.
- Boring insects such as the emerald ash borer or the bronze borer, which attack ash and birch trees, respectively, contribute to leaf loss at the crowns of trees. Emerald ash borers are deadly and untreatable, but birch borers and other pests that cause leaf loss are controllable. Regular pesticide sprays beginning in the early spring will help control the presence of harmful insects on the trees, reducing the likelihood of leaf loss and damage at the top of the tree.
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