Answer: Without seeing the problem firsthand, I can only relate the most common walnut tree problem with the symptom you describe. There's a disease (Xanthomonas) that infects walnut trees and causes gall-like growths on the stems, twigs, branches and trunk. These usually appear in the spring as pink growths and later change to brown or black. The infection is most active just as the tree begins to flower and the infection can be splashed by rainwater onto the leaves and fruits of the tree. If the fruits are affected you'll discover slimy black areas on and in the nuts. Next spring, just as the catkins are opening, you can spray the tree with a fungicide to protect the fruit. For now, just clean up the fallen leaves and fruit so fall and winter rains can't splash the pathogen onto the tree. Next spring use a lime-sulphur fungicide to protect the tree.
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