Anthracnose is one of the most common foliar diseases of landscape trees. It can impact virtually any species, though some, including sycamores, oaks, maples, ash and dogwood, are more susceptible to infection. Foliage of infected trees is often unsightly with discolored or dead “spots” on the leaf surface or along leaf veins.
Anthracnose is caused by fungi that overwinter in twig cankers. In spring, anthracnose fungi produce spores that infect susceptible plant tissue. Cool, moist weather provides ideal conditions for disease development and heightens the severity and spread of the disease.
In many instances, the impact of anthracnose is largely aesthetic. However, heavily infected leaves may fall prematurely or a tree may become completely defoliated if the disease is severe enough. Several years of infection also worsens the impact on tree health. Trees under stress from improper irrigation, lack of available nutrients, severe weather, injury or other issues, will have a more difficult time withstanding infection.
Properly timed treatments can help control anthracnose and prevent development of the disease. More frequent treatments are often needed when it is cool and rainy.
Any diseased leaves that fall prematurely should be collected and destroyed. In autumn, when the remaining leaves fall, these should also be collected and destroyed. Diseased twigs and branches should be pruned out. This will help eliminate the source of the fungi and help in preventing reinfection.