Anthracnose is a common foliage disease of shade trees in Iowa. Symptoms occur on sycamore, ash, maple, oak, walnut, linden, hickory, and other deciduous trees. Anthracnose is caused by a number of different but closely related fungi. Each fungus is specific to the host tree it affects.
In most cases, although symptoms may appear serious, damage caused by anthracnose is minimal and does not seriously harm established shade trees. Symptoms vary from small, circular to irregular spots that are tan, dark brown, or black, to larger blotches that are usually associated with midribs and veins. When immature leaves are infected, these leaves may become distorted from abnormal leaf expansion. Young leaves may die and fall soon after a heavy infection. If a severe infection occurs early in the growing season and the trees defoliate, a new set of leaves may emerge. Sycamores may also show bud, shoot, and twig blight in addition to blighted leaves.
The following suggestions will aid in decreasing the severity of anthracnose and minimize its impact on tree health.
- Clean up and destroy as many fallen leaves as possible. This will help reduce the overwintering population of anthracnose fungi.
- Prune the tree to remove diseased twigs and branches (primarily for sycamore anthracnose) and to open up the canopy for better air circulation and light penetration.
- Maintain tree vigor with proper watering, fertilization, and other cultural practices such as mulching.
- Select species that are resistant or less susceptible to anthracnose.
- Apply a labeled fungicide when warranted. Research and experience show that fungicide control is rarely warranted because anthracnose usually does not seriously damage tree health and adequate control is seldom achieved.