Tar Spot (Rhytisma acerinum)
Common Name(s):Tar Spot
Scientific Name(s):Rhytisma acerinum
Principle Host Trees & Shrubs:
Sycamore and other Maples (Acer species).
Description, Development & Diagnosis:
The fungus overwinters on fallen leaves. Fresh spores are produced in Spring which have a sticky coating. The spores attach themselves to the new leaves as they form. A raised, shiny black spot appears on infected leaves.
Common. Can cause premature leaf drop but the vigour of the tree is rarely affected. Rarer in cities due probably to fewer fallen leaves left under trees.
Generally unnecessary. If a problem on ornamental species dispose of fallen leaves in Autumn to reduce spore levels in Spring.