Birch trees are susceptible to several fungal diseases, some of which can be fatal. The best course of action with fungal diseases is prevention. Fungus needs moisture to grow. Make sure water does not stand on the leaves and puddles do not from around the base of the tree. They are most susceptible when the spring weather is wetter than usual, and they need to be watched. Remove and destroy any fallen debris from infected trees so that the disease does not spread.
Birch Leaf Blister
Birch leaf blister mostly attacks gray, white and yellow birch trees. It is a fungal disease that appears as bulges or blisters on the leaves. It first appears in the spring before the leaves have a chance to fully develop. It will stay this way until mid--summer when you will notice the bulges or blisters becoming darker and turning brown. It is at this time that the fungus grows spores. The skin of the leaf will burst, allowing the spores to be disbursed. They spend the winter in the new bud scales and re-appear the next spring. Spray with a fungicide in the spring before the leaves appear to kill the fungus.
Birch Leaf Rust
Birch leaf rust is a common fungal infection. It appears later in the growing season as small red or yellow bubbles on the bottom surface of the leaves. The leaves will turn yellow and drop off and in the worse-case scenario, the tree will loose most of its leaves. Spraying with a liquid copper fungicide early in the spring can help prevent rust.
Most leaf spots are caused by fungal infections. Once the fungi get into the leaf, they grow and multiply, destroying the living tissue. The dead spots on the leaves can be brown, black, tan or red, sometimes with a red or purple border. The tree can become completely defoliated. All types of trees are vulnerable to leaf spot, but the type of fungus is not necessarily the same. A tree of one species that is planted near a different tree that is infected may not be in any danger of catching the disease. By the time the spots appear, it is too late for any fungicide to be effectual, so under normal conditions spraying is not recommended. If the tree is under any stress from being transplanted or under attack from insects, leaf spot can be fatal and spraying is a necessity.
This is another fungal disease of birch trees. It appears as a swelling near places where the tree was not pruned properly or where branches have broken off. The swelling expands, cuts off the water supply to an individual branch or the whole trunk, causing the death of the infected part. Cankers should be pruned away as soon as possible.