The magnolia family consists of a combination of evergreen and deciduous trees and shrubs. These trees are hardy and showy trees that thrive in well-drained locations with full sunlight. With more than 80 species, there is a magnolia that can thrive in every growing zone. These trees are fairly pest and disease resistant. However, magnolia trees are susceptible to several bark diseases.
Nectria canker is a fungal disease that penetrates the wood of magnolia trees. Transported by fungal spores, this canker disease infects the tree through its wounds. The point of infection develops an elongated lesion and the bark becomes discolored. Progression of the disease results in the development of bark cankers and calluses, as well as growth stunt and dieback of branches, stems and foliage. Stressed magnolia trees are especially vulnerable to this disease. There is no cure or treatment for this canker disease. The disease can be controlled by pruning away the infected areas. Severely infected magnolias should be removed and destroyed.
Wetwood, also referred to as slime flux, is a disease that is caused by a collection of bacteria. Like many tree diseases, wetwood infects the magnolia tree through open wounds and natural openings. This bacterial infection causes the infected wood to become water-soaked with bacterial ooze. This ooze seeps through the infected wood, causing the bark to discolor, crack and decay. The ooze emits a foul, rancid odor, along with a gaseous release, and will kill surrounding vegetation upon contact. Wetwood cannot be cured with bactericide treatments.
Armillaria Root Rot
Armillaria root rot, or shoestring root rot, is a soil-borne fungal disease. This disease infects weakened and stressed magnolias, such as those that are drought stressed, frost injured or previously diseased or infested. Entering through the tree’s root system, armillaria root rot causes the decay of the tree’s fine, feeder roots while causing the rapid decay of the tree’s wood and bark. Infected magnolia trees will also experience yellowing of foliage, dieback and growth stunt of branches and premature defoliation. Severely infected magnolia trees will also ooze a liquid from their trunks. The trunk of the infected tree will develop yellow- to white-colored fungal deposits and mushrooms. While there is no cure for an infected tree, the disease can be prevented by maintaining a vigorously growing tree. Fungicidal treatments are effective in reducing the magnolia’s susceptibility to this disease.