Phyllosticta Leaf Spot

It is very difficult to identify a disease from a photograph, but your problem may be due to a fungus that begins with irregular, roundish, yellow-brown spots or lesions and as the disease progresses will form black target-like spots in the center. Fungal spores are spread by wet weather when leaves are splashed by the spores. Remove and destroy affected leaves including the foliage that has fallen to the ground, do not water overhead, but instead at the base of the plant, water regularly.Suggest you take a leaf sample to your local garden center for confirmation and if it is, unless the fungus is widespread, it should not harm the tree, but if it is widespread, eventually this will weaken it. A copper fungicide may be the appropriate treatment for control.