Leaf spot and melting-out (of meadow-grass)

Symptoms

First, small purplish-brown to black spots and dashes on the leaf blades and sheaths, often with a tan centre and dark border. As the disease moves into the melting-out phase the infection spreads down into the leaf sheaths, crowns and roots, rotting them so whole plants thin out and die in diffuse patches — the lawn looks generally thin and ragged rather than sharply ringed. Worst on Kentucky bluegrass (Poa pratensis) in cool, wet spring and autumn, especially under low mowing and high nitrogen.