The evergreen Southern magnolia (Magnolia grandiflora) tree attains a height of approximately 80 feet with a 40 foot spread. The tree produces large, saucer-sized, fragrant, white blossoms. The leaves often measure 8 inches in length. Commonly grown as a specimen landscape tree across the Southern United States, the tree is hardy and suffers from very few pests. The Southern magnolia does require abundant water, between 40 to 80 inches per year, to maintain health.
Cercospora fungal infections produce leaf spots that appear as small gray or brown dots on the tree's foliage. The dots are often outlined in black. The spots produce holes throughout its surface. Eventually the leaf will turn brown and drop to the ground. The disease does not need treatment to control. It occurs on the Southern magnolia tree from June to August when the humidity level is high. Once the humidity level is reduced the leaves infected with the fungus are shed and the tree returns to its healthy state.
Cristulariella fungus produces brown and gray spots on the leaf's surface that often appear like a target or bulls-eye. The fungus produces numerous spots until the leaf falls from the tree. The fungus is found predominately in magnolia trees planted in shady locations. Control is not needed. The fungal infection will run its course and the tree will eventually return to health despite an unsightly appearance for a short time.
Anthracnose fungus produces drying and brown areas along the outer edge of the magnolia tree's leaves. The drying spreads to engulf the entire leaf until it falls from the tree prematurely. The Anthracnose fungus occurs after abundant spring rains. Gather all leaves that fall under the tree and destroy them to prevent the spread of the fungus. There are numerous fungicide treatments that control and help prevent Anthracnose from spreading.
Nectria canker produces large lesions on the magnolia tree's branches and trunk. The cankers eventually spread to girdle the entire branch or trunk of the tree, which eventually results in its death. The fungus afflicts trees in the spring and fall. Branches and stems stricken with Nectria canker will wilt or fail to produce foliage. Prune any areas that show signs of canker and dispose of the branch. Quickly eliminating the diseased areas and helping the tree to regain its health will often halt the spread of the canker.