My walnut tree seems to have anthracnose disease. What should I do to try and...
Anthracnose, a fungal disease can be prevalent during cool wet springs.followed by a few days of warm weather. Many homeowners have been reporting this. You may notice browning along the leaf veins. Anthracnose can affect oak, sycamore, ash, maples, etc. No control is necessary. Rake all fallen leaves to prevent overwintering spores. http://extension.umd.edu/learn/shade-tree-anthracnose
As you have observed, this does not kill the tree. However, it can be defoliated by mid summer. Fungicides are not practical for large trees.