Leaf spot and melting-out are turfgrass fungal diseases that can cause indefinite yellowing and thinning of grass, as well as large patches of dead turfgrass.
Cool-season turfgrasses, especially Kentucky bluegrass, are most susceptible to leaf spot and melting-out diseases. A landscape professional can tell you which turfgrass cultivars are most disease-resistant in your growing region.
Prolonged periods of cool to warm and humid conditions can lead to these diseases, although the melting-out phase is often not evident until it’s warm and dry. Look for a yellow to rust-colored cast over all or part of the lawn, as well as yellow-brown spots with purple-black borders on grass leaves.
Follow a preventive maintenance program as prescribed by a certified arborist, including applying fungicides if appropriate. To help limit the severity of the disease, seed or sod with disease-resistant cultivars, remove excess thatch, never overfertilize and try not to water in the early evening.