Well, a good soil, feeding and mulching would promote healthy growth, trees need more than just water to thrive so that would be my first strategy to help the tree recover.
What your tree is specifically suffering from I am not really sure. It could be the beginnings of dieback or walnut blight. The shrivelled leaves might be frost damage but I would think more leaves would be affected if it was that. Mine suffered bad frost last growing season resulting in major leaf and bud damage and no walnuts.
Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
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What your tree is specifically suffering from I am not really sure. It could be the beginnings of dieback or walnut blight. The shrivelled leaves might be frost damage but I would think more leaves would be affected if it was that. Mine suffered bad frost last growing season resulting in major leaf and bud damage and no walnuts.