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. Make sure plants have adequate soil moisture. This information is for educational purposes only. References to commercial products or trade names does not imply endorsement by MSU Extension or bias against those not mentioned.