Limb Rotting in a Japanese Magnolia

Canker Diseases

• The Japanese magnolia (Magnolia x soulangiana "Alexandrina") is also called a saucer magnolia. The limbs and branches of the tree are susceptible to canker diseases that cause them to rot and display open wounds on the appendages. Several species of Nectria canker infect many hardwoods -- including magnolias -- and fruit trees in the U.S. A canker is a sunken area on a twig, trunk or branch that holds dead tissue and is encircled by layers of callused tissue.

Canker Symptoms

• One of the first symptoms of canker infection is foliage that turns yellow or brown and wilts or dies, often defoliating the tree prematurely. Peeling the bark back from a limb rotting in a Japanese magnolia will show a discoloraton of the sapwood. A sticky resin seeps from the infected branch. As the disease progresses, the limbs become girdled -- strangled -- and proper nutrition and water cannot flow through the area, resulting in the death of the branch and surrounding foliage.

Disease Management

• The pruning away of dead leaves and rotting branches is crucial in the management of canker. Once the disease spreads to the main trunk there is little likelihood of preventing the eventual death of the Japanese magnolia. The chief strategy for canker prevention is the planting of resistant varieties and the maintenance of the overall health of the tree. Gardeners should also be careful to avoid wounding the bark of the tree and introducing a condition known as wetwood or slime flux. This bacterial problem causes rotting limbs in a Japanese magnolia.

Heart Rots

• Fungal diseases called heart or sap rots invade the tissue of tree limbs and produce a strong decay of the wood within. When faced with this problem, the limbs of a Japanese magnolia are capable of rotting within a short period of time, ranging from months to a few years. Older, weaker trees are the most susceptible, and the fungal disease produces the growth of mushrooms on the limbs, trunk or base of the tree.