Causes & Symptoms
Anthracnose is a fungal disease that can affect multiple species of trees, most notably Maple, Oak and Ash. Cool, wet spring weather are needed for this fungus to thrive. If these conditions occur, it is fairly common to see species of oak, maple and ash trees showing symptoms that include brown spots on leaves, curling or distorting of leaves and leaf drop.
Typically, Anthracnose is most prevalent on the lower, inner branches where humidity levels are generally higher. On oak trees, this characteristic helps differentiate Anthracnose symptoms from those of Oak Wilt, a much more serious, systemic fungal disease. These symptoms typically show up in late spring or early summer and can cause defoliation of a tree, which creates a bit of concern for tree owners. However, the leaves typically drop early enough in the season that a healthy tree will 'push out' a second flush of growth.
Anthracnose generally is not considered a threat to the life of a healthy, vigorously growing tree. But, stressed trees, due to other factors such as drought, insects or root problems, or any tree that experiences repeated, severe de-foliations over several consecutive growing seasons, are more susceptible. Treatment applications for anthracnose are generally not needed for healthy, vigorously growing trees.
Cultural practices that should be implemented include proper watering of trees, mulching (to help retain moisture in the soil) and raking up the leaves in the fall and properly disposing of them (don't just blow them into the woods, mulch them with a lawn mower, or keep them for composting because the fungal spores overwinter on the leaves and if left on-site, it can increase the chances for re-infection the following year).