Common Tree Disease

The majority of tree disease are a result of some kind of bacteria or fungi. There are thousands of bacteria and fungi, and illnesses are spread through a variety of methods. Our job as Certified Arborists is to undergo a process to accurately diagnose your particular tree disease. These diseases are the cause of significant replacement expense of trees in landscapes and the commercial expense of future losses of forest products. This list does not include the Emerald Ash Borer.

Tree Disease

  1. Dutch Elm Disease. (DED) is really a very known fungal illness infecting the general system of the American Elm. The fungus results in the clogging of vascular cells stopping water movement, causing tree wilt and eventually death. Symptoms consist of dying branches, and the very best method to diagnose DED would be to cut a live branch to figure out if there’s brown streaking in the sapwood. The economic loss resulting from death of high value urban trees is considered by many to be “devastating”.  American elms are highly susceptible.
  2. Tree Blight. This tree disease is brought on by a bacteria or fungus. Trees with blight show wilt, browning of leaves, dying of leaves or twigs in significant portions of a tree.
  3. Fire Blight. This tree disease is brought on by a bacteria that impacts mainly Apple and Pear trees. Fire blight is a serious disease. This tree disease occasionally will damage crabapple, hawthorne, mountain ash, ornamental pear, firethorn, plum quince and spiraea. Fire blight is caused by the bacterium Erwinia amylovora, can affect many parts of a susceptible plant but generally noticed first on damaged leaves.
  4. Scab. A kind of Fungus that typically is found on the fruit of Apple trees, first as wounds on the leaves, then as a hardened or cracked scab on the fruit.
  5. Sudden Oak Death.  A strange phenomenon known as Sudden Oak Death was first reported in central coastal California. Since then, tens of thousands of oaks and California black oaks have been killed by a newly identified fungus, Phytophthora ramorum. On these hosts, the fungus causes a bleeding canker on the stem.
  6. Leaf Spot. Little areas of expired tissue on leaves.
  7. Blotch. A kind of Fungus that results in black or brown smears on leaves, bigger than leaf spots.
  8. Leaf Scorch. Can impact a number of tree species, generally brought on by climate extremes. Results in browning or dead locations of a leaf usually toward the leaf ends around the circumference.
  9. Oak Wilt. A Fungus that impacts mainly Red Oaks, spread by insects via root grafts. Outcomes are often leaf discoloration, wilt and drooping of leaves because of lack of water, defoliation, and eventually death. Oak wilt, Ceratocystis fagacearum, is a disease that affects oaks especially red oaks, white oaks, and live oaks. It is one of the most serious tree diseases in the eastern United States, killing thousands of oaks each year in forests and landscapes. The fungus, like all tree diseases, attacks wounded trees. The wounds promote infection. The fungus can move from tree to tree through roots or by insects. Once the tree is infected there is no known cure.
  10. Verticillium Wilt. A soil born fungus, results when the leaves (generally in branch sections) on a tree all of a sudden yellow, wilt, and die. The wood and vascular system below the bark from the infected a part of the tree is discolored in streaks.
  11. Armilarria Root Rot. A soil born fungus, generally known as ‘shoestring root rot’. This tree disease attacks hardwoods, softwoods and kills shrubs and vines in every state. It is pervasive in North America and a major cause of oak death. The Armillaria spore. can kill trees that are already weakened by competition and tree pests. The fungi also infects healthy trees, either killing them outright or weakening them so they can be easily attacked by other fungi or tree insects. Root like structures known as Rhizomorph’s are produced and spread the fungus.
  12. Anthracnose. A fungal tree disease that causes leaf blight. Generally impacts Dogwood, Ash, Oak, and Sycamore trees. Outcomes in brownish blotches and discoloration along leaf veins.
  13. Canker. Fungus that forms dead tissue of the bark and cambium on branches. Outcomes in dead areas of the bark.
  14. Hypoxylon Canker. A fungus that mainly impacts Oak trees probably induced by drought, outcomes in dead areas in the bark. Hypoxylon Canker is extremely simple to identify because the bark turns a light grayish white.
  15. Leaf Blister. A fungal leaf spot tree disease that appears comparable to a human blister. Generally pale green and swollen spots on a leaf, most typically impacts Oaks.
  16. Rust. Fungus causing orange or reddish brown swollen locations on a leaf. Mainly seen on Apple trees.
  17. Gall. An abnormal development of tree tissue brought on by parasites from fungi and bacteria, insects or mites. Appears like a sizable growth on the trunk, branch, twig, or leaf.
  18. Chlorosis. Yellowing of leaves because of lack of Chlorophyll. Usually brought on by lack of nutrients in soil, higher PH, drought, or soil compaction. Usually, the leaf veins will remain green but the rest of the leaf yellows.
  19. Necrosis (dead tissue). The death of cells or tissue brought on by injury or illness.
  20. Die-back. The dying of tree branches, beginning at the tips.
  21. Powdery Mildew. White powdery spots on leaves or stems brought on by a tree disease fungus. As spots get bigger, spores are formed and spread the illness to other components from the tree. Numerous tiny black dots are another kind of Powdery Mildew. Typical on Lilac, Crab Apple, and Sycamore.
  22. Sooty Mold. A black development around the surface of leaves that grows on honeydew deposited by aphids.
  23. Black Knot. A swelling on the bark brought on by a fungal tree disease. Typical amongst cherry and plum trees.
  24. Shoe String Root Rot. A fungal illness that appears like stringy fungus. Shoe String root rot appears above ground throughout the growing season in the base and surface roots of a tree. Typical amongst Oak trees.
  25. Girdling Root. A circular root that grows about the base of a tree. This is not really a tree disease, more of a function of poor planting. Because the trunk expands, the root cuts off the circulation of vascular flow to the leading areas of a tree. Usually brought on by a pot where tree roots began to grow.

These tree diseases can be diagnosed by a certified arborist. Do not try to diagnose a disease tree by yourself. The symptoms of so many diseases are very similar.

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