Powdery Mildew of Grass
Blue-grass lawn in picture has been devastated by powdery mildew that can eventually cause death of the infected host. You can see the healthy lawn to the rear and to the right with large patches of diseased (dead and dying) grass in the foreground. The disease is caused by the fungus Erysiphe graminis that affects a wide range of graminaceous hosts including cereals.
With serious infections the powdery growth of the fungus can completely cover the grass blades with a fine layer of hyphae and spores(CLICK HERE).