Powdery mildew leaves a white powdery look on your lawn, almost like someone dropped some baby powder. While it can kill the lawn, usually it’s easily remedied. The most common reason for it is excess water in the spring or fall, so the best method is to use practices that allow the grass to dry out as much as possible. If you are mowing tall, drop it down a notch or two so the blades aren’t holding in moisture. If you are watering, dial back the water. Usually this is enough to take care of the issue.