This section is from the book "Commercial Gardening Vol3", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
This fungus forms greyish blotches up to 1/4 in. across on living Walnut leaves. These patches become dead and dry and fall away, leaving holes in the leaf. As a rule but few patches are present on a leaf, and the injury is slight, but every now and again there is an epidemic, when the leaves fall early in the season, which means badly matured and dwarfed shoots. The remedies suggested for the previous disease are applicable in the present instance, only the fallen leaves need not be troubled about, as the fungus has been carried away on the dead pieces of leaf that dropped out before the leaves fell.