The river birch is a favorite tree in the southern United States, because it can tolerate dry conditions. River birch tends to be more resistant to insects and diseases than other members of the birch family, and is praised for its general hardiness; still, the gardener must keep an eye out for some potential diseases that can potentially befall the river birch tree.
Leaf blight is one disease that affects river birches. It causes the trees to lose up to 40% of their leaves during the summer. It is caused by the leaf blight fungus that thrives in wet conditions. The first symptom is the appearance of extremely small brown or black spots on the youngest leaves. They will pop up during the summer and not only get larger, but spread to other leaves as well. They are easily distinguishable by the yellow circle that surrounds each of the spots. It will make the tree look sick, but since it still has a good portion of its leaves intact, it luckily will not die. The fungus will not spread to other parts of the tree either. Affected leaves, which will drop to the ground, should be gathered and burned so the fungus will not attack again the next year. Proper fertilization is a good way to prevent the onset in the first place.
Shelf Fungi Root Rot
Shelf fungi root rot is one of the most serious diseases that can strike a river birch. The fungus sticks out from the tree like it was on a shelf, hence the name. Two distinctive types exist. One has a soft structure that has the ability to replace any part that is destroyed. The other has a hard structure called conks, which grow slowly. They can appear as mushrooms or puffballs. The fungus feeds on dead wood, and can be insidious: If the exterior of the tree is healthy, the interior could be rotting away unnoticed because the parts of the tree involved in producing leaves is perfectly healthy. A tree that is decaying from the inside is in danger of falling.
Birch canker is a fungal disease that is becoming more and more common. Check the places where the tree has been pruned. There, canker will grow if the pruning has not been done properly, if the branches are broken or if there is a cut in the branch or trunk. Remove cankers in the branches by pruning.
Rust is an infection that is often found in river birch and other types of birch trees as well. A small red or yellow bubble will appear on the lower part of the leaf late in the season and can cause the leaves to turn yellow and fall off. The fact that it appears at the end of the season makes control easy. Pick up and burn all of the fallen leaves; and the next spring, just when the buds break out, spray with a liquid copper fungicide, then do it twice more at 2- to 3-week intervals.
Birch dieback causes branches, or parts of the branches, to die. It can affect just a cluster of branches or one whole side of a tree. Birch trees have shallow roots, and therein lies the problem. Shallow roots can be damaged by heat. Fallen leaves can protect the roots, so when they are raked up, the roots lose their protection. An early freeze can also kill off branches, as can warm weather in late winter and/or early spring. Light watering or drought conditions will not get enough water to the roots and a poorly drained soil, will not let excess water drain away, causing root damage. This will not only cause dieback, but will leave the tree susceptible to other diseases and bug infections. Prevent dieback by planting the tree where it will get at least some shade and using an organic mulch.