Anthracnose is a generic term for a group of fungal infections that cause leaf spots and blotches, twig cankers and defoliation of a wide range of tree species. Anthracnose infections are difficult, if not impossible, to cure once they're established, and without proper control, they can return to affect the same tree year after year.
General Tree Health
The primary threat of anthracnose is that it weakens infected trees and makes them susceptible to other pests and diseases. Therefore, maintaining the overall health of and reducing stress on an affected tree is the best way to help the tree survive an anthracnose infection. That means watering the tree adequately and fertilizing it with a balanced fertilizer, if necessary, depending on the local soil conditions. Fertilization may be especially helpful if a tree has suffered from an infection over more than one season.
Moisture Control and Air Circulation
Anthracnose fungi are spread via water, and they grow best in wet conditions, so control of excess moisture is critical in preventing and controlling infections. Trees are susceptible to infection if their leaves remain wet for a prolonged period of time, so avoid placing sprinklers or other irrigation systems so that water is directed onto trees' canopies. Pruning trees so that air and light can more easily penetrate their canopies will help to control moisture and limit the growth of the fungus.
Pruning and Raking
Although anthracnose infections are difficult to control in infected trees during the growing season, proper maintenance may prevent a repeat infection the next season. Anthracnose spores will survive through the winter in infected leaves and twigs, and the overwintered spores may re-infect trees the following season. Pruning infected twigs and raking, removing and destroying fallen leaves from infected trees will reduce the number of spores in the area and lessen the chance of re-infection in subsequent seasons.
To be effective in preventing infections, fungicides must be applied in the spring before an infection can be established; fungicides won't kill the fungus on affected leaves and twigs and will only prevent the growth of fungus on healthy new growth. Because the correct timing of fungicide application is difficult to determine and large trees are difficult to treat effectively, the use of fungicides to control anthracnose is not generally recommended.
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