I am not certain I could have predicted the extent of anthracnose we have seen on shade trees in Illinois this year. Because the anthracnose fungus thrives in wet weather and cool temperatures, initial infection was expected. Secondary infection does occur, but older leaves are less susceptible to infection by anthracnose fungi, and symptoms are usually masked by healthy new leaves in early June. Because growing conditions were cool for much longer than normal this spring, foliage was susceptible longer than normal. Required leaf wetness has been a common factor in much of Illinois as well. Consequently, we are still seeing sycamores with thinned canopies, and oaks, ash, and maples with many anthracnose lesions. The image shows some oak leaves received by the Plant Clinic. These are from central Illinois and were showing symptoms the second week in June.

Scattered brown lesions are typical of anthracnose. Sometimes the foliage is twisted or slightly distorted as the healthy growth continues to grow and the infected tissues shrivel.