The Birch genus (Betula spp.) consists of about 30 species of deciduous, medium-sized shrubs and trees. Generally, they are considered short-lived plants, particularly in regions with hot, dry summers. A birch with damaged bark may suffer from a disease or pests, likely as a result of mechanical damage or improper cultural conditions.
Canker is a fungal disease that causes yellow, orange, brown or black bark on the trunk and branches of birch. Discolored areas may ooze liquid or be sunken and spotted with black dots. Stress from cultural conditions and open wounds on the trunk or branches are the most common causes of the disease, according to "IPM for Select Deciduous Trees in Southeastern U.S. Nursery Production." No cure exists for canker. Remove infected trees to prevent the disease from spreading to nearby trees.
Birch trees are susceptible to many pests, though the bronze birch borer is the only pest that causes notable injury to bark. Bronze birch borers tunnel under the trunk, causing the bark to become wet, sappy and cracked. If left unchecked, the pests can lead to the death of branches or the entire tree. Remove and destroy infested limbs. River birch (Betula nigra), which is hardy in U.S. Department of Agriculture (USDA) zones 4 through 9a, is less susceptible than other birches to the borers.
Wood decay is a common culprit in large, old birch trees. The disease starts in the heart of a tree, rotting the tree from the inside outward. Oftentimes, the only noticeable symptom from the outside is the presence of mushrooms, such as turkey tails or artist's conk, attached to the bark. Wood decay is dangerous because it eventually hollows out the tree, causing it to collapse. A decaying tree must be cut down, supported or removed to prevent harm to other trees and property damage.
Healthy trees are less likely than unhealthy trees to fall prey to pests and diseases. Birch trees grow best in full sunlight and moist, acidic soil enhanced regularly with fertilizer. Borers often prey on trees that are stressed due to inadequate irrigation. Disinfect pruning tools with diluted bleach or a commercial disinfectant. If you observed fungal problems in the trees in the past, then consider applying a preventative fungicide to all pruning cuts. Avoid accidentally nicking a birch tree's bark when mowing or using a weeding tool.
- IPM for Select Deciduous Trees in Southeastern U.S. Nursery Production; Chapter 4, Birch -- Betula Spp.; Amy F. Fulcher and Sarah A. White, Editors
- Colorado State University Extension: Cytospora Canker
- University of California Integrated Pest Management Online: Managing Pests in Gardens -- Trees and Shrubs: Invertebrates -- Flatheaded Borers
- University of Florida IFAS Extension: Betula Nigra -- River Birch
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