Magnolia trees are a popular landscaping tree because of their fragrant, easily-recognizable blossoms and their large, green, glossy leaves. When cultivated properly, these trees can live for decades or even longer. However, there are a number of diseases that affect magnolia trees, and if you are not aware of early signs and symptoms of problems, you could lose your magnolias prematurely.
Magnolia wilt is caused by a fungal infection called verticillium. You may notice that the usually crisp edges of the leaves of your tree may have become crumpled and wilted. They may also turn brown. Remove the affected areas of the tree using sterile pruning techniques and fertilize your tree with a fertilizer high in nitrogen. In most cases this will strengthen the tree sufficiently to fight off the infection, although you should still monitor the leaves for wilt and remove infected leaves and branches.
A number of different types of infections can cause a variety of leaf spots on magnolias. Bulls-eye leaf spot forms a red or yellow ring on the leaf with green in the center. If enough of these form on a leaf, the leaf will fall. Other fungal infections can lead to red, yellow or brown leaf spots that may rot away over time, leaving "shot-holes" in your magnolia leaves. This is particularly common after wet springs. Leaf spot is largely a cosmetic problem, but left unchecked it can result in serious defoliation that can hurt or kill the tree. Sterile pruning and careful monitoring and removal of affected leaves will keep your tree happy and healthy.
Magnolia cankers are caused by a fungus called nectria. It is most active in Spring and Fall, but remains in the tree year-round. It is first evidenced by a depressed, discolored area of bark near a wound in the tree or at the base of dead or dying twigs or branches. This area will turn red or white, then develop a "callous" structure that looks like a cork that has been stuck in the tree. While this will not kill the plant immediately, it can affect growth patterns, stunt the tree and do significant cosmetic damage. Over time, a canker can spread and ultimately kill the tree if you do not treat it by removing the canker during a dry spell, which lessens the possibility of an infection.