Use nitrogen sparingly. Soil test and lime if necessary and provide plenty of potassium. See other recommendations I have listed below. Melting out attacks the bases of the leaves with a dark rot. After this, the leaves yellow.
Spots can be three inches to a foot or more in diameter.
They can slowly get larger. Do not over-fertilize. Remove thatch and spray as needed. General disease control practices work on all diseases. De-thatch if necessary.