Anthracnose is a fungal disease that causes leaves to brown and drop in middle to late summer. Many tree species exhibit the symptoms of anthracnose, but the different fungal strains that cause Anthracnose symptoms are species-specific. Wet spring weather increases the presence of the disease. Anthracnose fungi overwinter in small branches on the tree as well as on fallen leaves.
Periods of mild winter weather activate Anthracnose fungi, causing the fungi to form cankers on the tree and resulting in twig dieback. Fruiting fungal bodies appear on dead twigs and fallen leaves in the spring. Wind and rain scatter spores from the fruiting bodies onto new leaves and shoots. The optimal climate for Anthracnose fungi is cool, rainy spring weather. Anthracnose may thrive throughout the summer, too, if conditions are favorable. Hot, dry weather is ideal for stopping the progress of the disease.
Pacific and flowering dogwoods, London planetree, American sycamore, and species of ash, oak, maple, and walnut
Prompt removal of fallen leaves and twigs can help reduce next year’s outbreak. Dead twigs and branches should be pruned and the crown of the tree can be thinned to facilitate better air circulation and drying in the canopy. Keep the tree healthy by providing appropriate levels of water and fertilizer; healthy trees are more resilient against disease than stressed trees. Fungicide treatment to control anthracnose may be administered in the spring, but it is not necessary unless the tree has recently been transplanted or has suffered repeated seasons of defoliation from the fungus.