Powdery Mildew

• Powdery mildew is caused by Erysiphe graminis fungal spores. These spores germinate and spread when temperatures range between 60 to 72 degrees F, according to North Dakota State University. In addition, high humidity favors powdery mildew. Generally, lawns planted in areas of shade, such as near trees and shrubbery, are at a high risk of developing the disease. Anywhere there is poor air circulation should be monitored for powdery mildew.
  
  

Symptoms

• White powder blanketing areas of the lawn is the first sign of the disease. When powdery mildew infects the surface of the grass blades, the blades eventually turn yellow. Lower leaves may die because of the infection, according to North Dakota State University. White powdery mildew may infect patches or small area of the lawn, rather than the entire yard. Left untreated, these areas spread but may not effect sunnier locations.
  
  

Prevention

• Prune over-hanging branches from trees or shrubs to increase the light and air circulation for the lawn. Areas where you cannot control the amount of light to the yard may need to be dug up and replaced with groundcover that tolerates low light. Grass types that thrive in the shade include St. Augustine, zoysia and fescues, according to Clemson University. If the area doesn't receive at least four hours of sunlight, do not grow grass in those parts of the lawn.
  
  

Treatment

• Seed areas infected with powdery mildew. Dead grass should be dug up and the area reseeded. If you leave dead areas in the lawn, weeds take advantage of the lack of competition and pop up. Broadcast seeds in these areas. Cover the seeds with 1/8 of an inch of compost. Water the area to moisten the soil. Keep the soil moist for two weeks, so that the grass seed germinates.