Leaf Spot and Melting-out
A fungal disease called leaf spot and melting-out is one of the most common turfgrass diseases in Iowa. The fungi that cause leaf spot and melting-out and the spots they cause can be found on most lawns without the occurrence of substantial damage.
In Iowa, outbreaks generally occur late spring through June, especially when weather conditions are warm and humid. In advanced stages, melting-out (thinning or death of the grass) may occur in large areas.
Newly seeded lawns and the presence of a turfgrass variety particularly sensitive to leaf spot and melting-out fungi can also contribute to severe outbreaks.
Insect or drought injury can mimic leaf spot and melting-out. If the symptoms are mistaken for drought stress, and water is applied to remedy the situation, grass health probably won't improve. In fact, additional moisture could cause the disease to become worse.
Cultural practices that maintain healthy turfgrass are essential for leaf spot and melting-out prevention and control. Maintenance of plant vigor can help avoid severe outbreaks when conditions are favorable for disease development. Fungicides are rarely needed to control leaf spot and melting out.
See this bulletin about leaf spot and melting out.