Deciduous trees shed their leaves at the end of the growing season in order to replace them with new leaves in the spring. These trees range from small shrubs to fruit trees to large shade trees. Overall, deciduous trees are more susceptible to disease because they encounter natural wounds in the fall from defoliation and develop tender new growth in the spring.
Powdery mildew is a leaf disease caused by fungal spores. These fungal spores generally infect young, developing foliage. However, foliage of all ages can be infected by powdery mildew. The infected foliage of the tree develops a dusty, white covering of mildew across their surfaces that are accompanied by tiny, black fungal spots. Easily treated by fungicidal sprays, powdery mildew is not harmful to the overall health of the tree.
A soil-borne disease, verticillium wilt infects deciduous trees through its root system. This vascular disease prevents the infected tree from transporting the water and nutrients that it needs to support itself. As result, the tree, in essence, becomes starved and experiences wilt and premature defoliation. There is no cure for verticillium wilt and gardeners should ensure that the area is disease-free prior to planting.
Leaf spot, or anthracnose, is a causal fungal disease. This disease develops on dead and defoliated debris that lies around the deciduous tree. The disease, transported by fungal spores, infects newly developing foliage in the early spring. The infected foliage develops small fungal spots that become enlarge and necrotic with age. Severely infected trees experience premature defoliation and twig dieback. Still, leaf spot is easily treated with a fungicidal treatment and pruning of the infected areas.
Bacterial wetwood, also known as bacterial slime, is a highly contagious tree disease that can also be transmitted through infected soil. This wood disease infects the central core of the tree. The infected tree will become water-soaked and develop a yellow streak down the center of the trunk. The yellowish area will begin to ooze slime through its cracks. The ooze is also accompanied by a foul smell as the pressure is released from the tree. There is no treatment for wetwood.
A bacterial disease, fire blight is a serious disease that is especially destructive to fruit trees. This disease is spread by bacteria that develops during the late fall and lies dormant on fallen debris during the winter months. These bacterial spores are spread by wind and rain during the spring months and infect the newly developing shoots and foliage on the tree. The flowers and shoots are the first areas to develop symptoms of fire blight. These infected areas ooze a watery bacteria that turns dark as it is exposed to the air. Infected areas also experience wilt, curling and distortion that eventually turn black and die. Developing fruit also become blackened with a scorched appearance. Fire blight is controlled and prevented with a combination of heavy pruning and bacterial spray treatments.