Anthracnose is a common fungal disease of London planetrees & sycamores. Spores spread in cool, rainy weather. The disease attacks leaves early in the spring, causing rapid wilting of newly emerging leaves. Larger leaves develop brown lesions along the main veins. Infected leaves eventually curl & fall by summer. Cankers may form on twigs & branches, affecting water & nutrient movement. This can cause dieback, even on larger limbs. Repeated annual killing of twigs results in clusters of old dead twigs and live branches creating what are called “witches’ brooms.”
Weather Influences
Frequent rain & cool temperatures enable anthracnose spores to spread rapidly. It is most active when temperatures are below 55 degrees.
Management
Unfortunately treatment options are limited & must be applied before or while buds are emerging. Foliar sprays can be affective on smaller-to-medium trees where full coverage can be obtained & only if weather cooperates with spraying. Cambium injections applied before budbreak offer the best results. However, the severity of the disease or need for treatment isn’t fully known at that time.