Powdery Mildew is a common problem on bluegrass lawns in shady areas. The mildew fungus, Erysiphe graminis, attacks the surface of the grass leaves, developing a fine, fungal growth that resembles a white powdery substance on the leaves. In dense shade, Powdery Mildew causes the affected areas of leaves to turn yellow, eventually resulting in the yellowing and dying of lower leaves or even in the death of plants. The fungus over-winters in dormant turf.
Powdery Mildew develops in areas of dense shrubbery or trees where there is poor air circulation, considerable shade, and high humidity. It is favored by temperatures of 60 - 72 F. In many cases, Powdery Mildew can be controlled by selective pruning of shrubs to allow better air circulation and greater penetration of sunlight. Where Powdery Mildew is a problem, avoid susceptible grass varieties or plant alternate ground covers.
Chemical Control - Because the disease rarely is responsible for any lasting damage to turf, there are few instances where the cost of fungicide application would be worthwhile. If the appearance of mildew-infected turf is absolutely intolerable, fungicides may be applied for effective control. A professional lawn care service should be contracted for the application.