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 spots on trees are very common and generally do not require spraying. Leaf spot may result in 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 trees that become defoliated are more at risk of suffering damage until they become established. The chief symptom of a leaf spot disease is spots on foliage.