Powdery Mildew

• Powdery mildew looks like white fine strands of cobweb-like growth on grass blades. As the fungal spores germinate and spread, the entire grass blade can appear white. Moreover, the disease can also spread through the wind. This fungal disease can spend the winter in dead debris in the yard or lay dormant in the grass. When temperatures or conditions are favorable in the spring, powdery mildew comes out of dormancy. The disease needs air temperatures to be around 65 degrees Fahrenheit, according to the University of New Hampshire Cooperative Extension.
  
  

Damage

• Grass blades covered in powdery mildew begin to discolor and turn yellow. If the disease goes untreated, the grass can die off. Because powdery mildew typically does not spread over the entire yard, you can see dead patches or thinning grass. Dead patches or bare areas give weeds the opportunity to pop up over the yard. Without grass competition, weeds can take over the lawn.
  
  

Increasing Sunlight

• Shady areas in the yard see the worst of the damage. However, you can increase the sunlight and kill off the powdery mildew. Prune back overhanging branches. If trees cast too much shade in the yard, consider removing them to increase the light. Keep shrubbery compact around areas that are heavily infested with powdery mildew. Increasing the air movement in the yard will help treat or prevent powdery mildew. Avoid planting trees or shrubs too close together.
  
  

Chemical Control

• Apply mancozeb or bayleton to the lawn to treat the powdery mildew. Apply chemical treatments on days that are rain free. Wear gloves, goggles, pants and a mask whenever spraying these products. Fungicides like mancozeb can cause headaches and nausea when used, according to Critical Habitat Project. Severe outbreaks may warrant chemical control every four to six days. Reduce the amount of nitrogen that you are applying to the yard. High nitrogen fertilizers can spread the disease.