Even with careful care, fertilizing and watering, it's still possible that even the most hardy trees will be struck down with disease. One of the most important steps in bringing trees back to health is recognizing the disease while it is still in its early stages, and to correctly diagnose the problem before looking for a solution. In some cases, diagnosing a disease for which there is no cure is also crucial. Sometimes the best offense is a good defense, which means removing the diseased tree and controlling the spread of the disease before it infects other trees.
Wetwood can take root in a number of different shade trees, including ash, hickory, beech, apple, sycamore, cherry and fir. While it's still uncertain what causes wetwood, the presence of bacteria in affected tissue has been found. The disease affects the core of the tree, and manifests itself in a yellowish coloring and a foul-smelling slime that oozes from between cracks in the bark. Stripping off a piece of the bark can reveal signs of wetwood in the form of dark streaks of discoloration. During winter, infected trees may display cracking wood.
Wetwood enters the tree through wounded roots. While there is no known way to completely eliminate wetwood, steps can be taken to control it. This includes cutting away affected tissue and inserting tubes to relieve pressure and drain away some of the slime.
Powdery mildew isn't lethal to a plant by itself, but makes it more vulnerable to other diseases. This fungus can infect almost any type of plant, but it is most common in dry areas. The beginning stages are characterized by yellow or green spots on the leaves, which will then develop into white patches. These white patches contain the spores, which are spread to new plants by the wind and passing animals. Powdery mildew can be contained by removing infected leaves and applying fungicide.
Anthracnose is another fungal disease that can infect a wide variety of plants and trees with varying degrees of severity. It is one of the most deadly diseases that can infect the sycamore, while other trees like the hickory are only mildly affected. Anthracnose can be difficult to diagnose, as there is only one species of fungi that infects each species of tree, and the signs of infection are always different. An infection in a sycamore will turn leaves brown and kill branches, while cankers--which produce spores--form on the bark. Oak tree leaves will develop a burned appearance as the edges dry and turn brown, while maple trees will develop purplish patches between the veins of their leaves. Disease control and elimination vary depending on the type of tree infected, but typically involves the use of fungicide.
Canker diseases can infect a number of deciduous trees, most often those that are subject to weather-related stressors. Canker diseases are characterized by blisters on the tree bark, which may or may not ooze. The infection contained in the canker can spread to other parts of the tree. The disease can be controlled if the infected branches are removed early enough.