These are round, black spots on leaves usually occurring during humid or wet weather.
There may be yellowing of the leaves, followed by premature leaf drop. Black spot also weakens the tree overall by reducing the area that it can take in sunlight through photosynthesis. Black Spot will rarely kill a tree but it can severely weaken the tree and make it more susceptible to other diseases.
Increase air circulation if possible and remove infected leaves. Watering should be done early in the day so that the leaves are not wet overnight. Drenching the soil, being careful not to splash water on the foliage.Spray with sulphur or Bordo.