Fungal bodies may appear as black dots in the spots, either in rings or in a central cluster. Over time the spots may combine or enlarge to form blotches. Leaves may yellow and drop prematurely. The organisms that cause leaf spots survive in fallen infected leaves and twigs. Some may remain in dead twigs on the tree.
Most damage occurs in spring.
During wet weather spores are released which may splash or be windblown onto newly emerging tender leaves where they germinate in the moisture and infect the leaf. Overhead watering can also provide prolonged wet periods that are ideal for spreading leaf spot diseases. Integrated Pest Management Strategies 1. Live with the disease. Most trees tolerate leaf spots with little or no apparent damage.