Common Tree Diseases: Anthracnose
Anthracnose is a group of fungal diseases that affect many deciduous and evergreen tree species. It causes dark sunken lesions to appear on leaves, stems, twigs, flowers, and fruit. Prolonged infection can lead to severe leaf blighting, and foliar dieback. Anthracnose diseases are common on ash, maple, oak, dogwood, and sycamore. They may also occur on beech, birch, elm, walnut, and linden, albeit with less frequency.
Causes and Symptoms
Anthracnose is most common on trees in landscapes, but it may also occur on trees growing in forested settings. The diseases associated with anthracnose are called leaf blights, leaf spots, or necrotic lesions. The severity and prevalence of anthracnose is influenced by a number of factors, including a tree’s genetic predispositions to disease, environmental stressors (such as drought, excess water, winter injury, or insect infestations), climate shifts, and severe weather. Anthracnose diseases are especially problematic during periods of cool, wet weather in spring.
Anthracnose fungi generally overwinter in infected leaves on the ground. They may also overwinter in dormant buds, branches, and twigs. Over time, infected branches and twigs will form cankers, eventually becoming blighted. Diseased buds are often killed outright. Infections of leaves, flowers, fruit, and stem tissues can occur in spring when new growth is emerging.
Symptoms of anthracnose vary by tree species, and the causal fungus. General symptoms range from minor necrotic spotting of leaves, to blighting of leaves and shoots. Severe infections can cause leaves to become distorted, and drop prematurely. They may also result in dieback of twigs and branches. Anthracnose diseases tend to have a greater impact on younger trees, and trees that have been recently planted.
Effects of Anthracnose
Anthracnose diseases cause aesthetic problems for trees. Severe infections may lead to significant defoliaton, as well twig and branch dieback. These injuries become more extensive as the infection progresses. If the infection persists over a number of years, the affected tree may decline.
Effective Management Practices
Anthracnose can be managed using the following practices:
- Prune and remove any dead wood from trees. Dead tissue is susceptible to infection from anthracnose fungi.
- Remove any symptomatic tissues from the tree, including infected leaves, branches, shoots, and twigs attached to or surrounding the tree. This will help reduce the number of fungal spores available to infect emerging shoots and leaves in spring.
- Maintain overall tree vigor by employing sound cultural practices.
- Ensure that trees are sufficiently watered, especially during dry periods.
- Fertilizing, mulching, and pruning are beneficial to trees. Applying a layer of organic mulch will improve soil quality, and promote healthy tree growth.
- For stressed trees, chemical control practices can be beneficial. Apply a fungicide spray just prior to bud break, before new leaves and shoots expand. Two or three additional sprays should be subsequently applied at ten to fourteen day intervals. Further applications may be necessary during wet or prolonged spring conditions.