Leaf spot and melting out are common diseases in turf grasses. This year in Northern Colorado, we are seeing a lot of outbreaks of Leaf Spot mainly because of atmospheric conditions and poor cultural practices. Leaf spot symptoms are the early stages of the disease, and if left uncontrolled, the pathogen progresses into the rest of the plant to cause ‘melting out’ which appears as brown blades of grass which can become widespread in a lawn. Leaf spot symptoms initially start as small, brown or black spots or flecks on the leaf blades as pictured below. As the lesions expand, the center of the lesions becomes tan with a darker brown or black border. They may also be surrounded by a yellow ring. As the lesions progress, they spread and combine to cause dieback of entire blades of grass and even plants. Melting out symptoms appear as a bronzing on a more widespread level than individual leaf spots which then leads to wilting, yellowing, and even death of the grass.
Leaf spot/melting out is most severe on turf that is growing slowly due to adverse weather conditions (heat or super wet conditions) or improper management practices. Shaded areas with little or no air movement result in weak turf and extended periods of leaf wetness favor disease development. Here in Colorado, excessive thatch, extended periods of leaf wetness (overwatering), drought stress, and low mowing heights (cutting grass too short) are factors which encourage the development of this disease. The spread and severity of this disease are during periods of hot weather. Leaf Spot and large areas melting out need to have multiple fungicide applications.