Steganosporium ovatum
Steganosporium ovatum is a fungal infection that causes black pustules to form on a tree's bark, often on lower, shaded branches. The pustules can eventually merge into a crusty black film. This infection is also known as twig blight.
Steganosporium can become a pathogen and kill branches if the tree is already weakened by other factors, such as drought, winter injury, or defoliation by insects. Trees that lose their first set of leaves to insects may use up valuable food reserves to grow a second set, which can lead to chemical changes that make them more susceptible to disease.
Symptoms of Steganosporium ovatum infection include:
Black fungal pustules: These pustules can merge together to form a solid black layer over the tree's bark
Blighted leaves: In severe cases, the fungus can enter the petioles of the leaves, causing them to appear blighted, shriveled, and browned
Leaf drop: The tree may experience significant leaf drop and premature defoliation
Steganosporium Ovatum Prevention
The only known way to prevent Steganosporium ovatum is to preserve the health of the maple tree.
Do not plant the tree too deeply; instead, plant it shallowly and surround the root system with 2 to 4 inches of mulch to prevent damage from overcultivation.
Refrain from using deicing salts near the tree, or alternatively, plant it away from roads to shield it from deicing spray.
During the winter months, wrap the young maple tree's trunk with burlap to safeguard it against winter scald.
Ensuring the tree gets at least an inch of water per week during dry spells.
Fertilizing the tree based on soil tests.
Avoid mounding fallen leaves around the trunk, as they can provide a shelter for the fungus and allow its spores to spread.
If you do need to remove an infected tree, it's best to do so in damp weather such as early morning to reduce the risk of spreading spores. You can also try burying infected material locally or transporting it in covered containers to be burned in a waste incinerator.
