Canker diseases cause dieback or death of trees. Infected bark may be discolored, sunken, or have a different appearance than surrounding healthy bark. Prune out infected branches and keep trees healthy. If the canker girdles the trunk the tree dies. Bacterial blight causes small, irregularly shaped spots on the leaves and leaf stems.
Black spots occur on young nuts and shoots.
Nearly ripe nuts have large black spots on the husks. Infected nuts fall prematurely or may have husks, shells, and kernels blackened and ruined. Powdery mildew causes a white coating on the leaves. Chemical controls should not be necessary. During periods of high temperature and drying winds, walnuts will scorch.