Verticillium Wilt

• Verticillium wilt is a soilborne disease that can kill magnolia trees. The fungus attacks the vascular tissues of the tree and can rapidly block the vessels carrying the water throughout the tree. The tree will show a decline in health if the tree is infected. Branches will start to die off or you will notice thinning of the branches. Determine if the tree has verticillium wilt by cutting off a dying branch. If the core is stained with brown or dark green coloring, it is possible the tree has the disease. Have the tree tested by your county extension service.
  
  

Nectria Canker Disease

• Nectria canker enters the bark of the magnolia tree through a wound. As the canker develops, trees will have lesions that appear elongated and the bark will start to change colors. As the disease progresses, calluses and cankers will cause branches to die back and stunt the growth of the branches, leaves and twigs. Remove dead branches, leaves and twigs infected by canker diseases from the tree. If the tree is severely infected, you will need to remove and discard it.
  
  

Algal Leaf Spot

• Leaf spot generally affects trees grown in the southeastern parts of the country where trees grow in warm and humid climates. Although the disease usually only affects the leaves of the tree, it can affect twigs as well. Magnolia leaves will have raised spots about 1/2 inch thick. The spots are orange, brown or grayish. When a severe infection occurs, the leaves will yellow and drop from the tree. To help prevent spread of leaf spot, rake up the fallen leaves and discard them. For severe infection, use a copper-based fungicidal spray.
  
  

Bacterial Blight

• Common in locations that have wet conditions, bacterial blight will affect a magnolia tree. Pseudomonas syringae causes this type of blight. The disease will cause brown, irregular-shaped spots on the stems, blossoms and leaves of the magnolia trees. Some spots on the leaves may be small, but the color will be brownish, almost black. Rid the tree of the disease by pruning away infected parts of the tree and discarding the infected parts. Do not fertilize the tree until all signs of the disease are gone.