Magnolia trees, a southern charmer reminiscent of an old plantation, can reach heights of 80 feet. Its large, creamy white blossoms are highly visible against stiff, glossy green leaves. Up close, you can smell the fragrant blooms and see that the undersides of the almost-foot-long leaves are reddish-brown. Like many ornamental trees, magnolias are susceptible to fungal and bacterial infections and other diseases.
Leaf spot may be caused by a bacteria or a fungus and may appear following a rainy season mixed with high humidity. The spot may be black with a yellow halo or may look like a bull's eye of concentric circles. Though leaf spot is unattractive, it doesn't hurt the tree. Collecting and disposing of fallen leaves can help reduce return infections. Bactericides may also help.
Powdery mildew is a fungus appearing as white to gray powdery blotches on the leaves of a magnolia tree. Spores from this fungus will float on the breeze, landing on other leaves and nearby trees. Removing infected areas can help reduce the spread of powdery mildew. Though the fungus causes no harm to the tree, it can be treated with a commercial fungicide.
Cankers display as bull's-eye-like lesions on the trunk or branches of a magnolia tree. When appearing on a branch, remove the diseased area by cutting into good wood at least 6 inches away from the canker. Cankers developing on the trunk of the tree can eventually encompass the perimeter of the trunk and kill the tree.
Verticillium wilt has the potential of killing the whole tree. A soil-based fungus enters through the roots. Leaves and limbs will wilt and die. Cut out infected areas. The whole tree may need to be removed, including the roots.