There are several fungal diseases that cause leaf spot. “Leaf spot” is a common descriptive term applied to a number of diseases affecting the foliage of ornamental and shade trees. The majority of leaf spots are caused by fungi, but some are caused by bacteria. Some insects also cause damage that appears like a leaf spot disease.Leaf spot may result in some defoliation of a plant. An established plant can tolerate almost complete defoliation if it happens late in the season or not every year. Small or newly planted that become defoliated are more at risk of suffering damage until they become established. Keep the leaves picked up that fall and destroy, do not compost them. Spray with a fungicide now and when new leaves emerge.