Powdery mildew is showing up in wheat fields across the Pee Dee right now. Powdery mildew develops readily when the humidity is high and temperatures are between 59 and 72. If you walk through a wheat field on a cool morning and your boots are wet by the time you leave, the environment is perfect for powdery mildew to develop. Any above ground portion of the plant can be affected. The photos below show what it looks like on leaves and stems.
Here is what it looks like under a microscope magnified 35x.
As powdery mildew progresses it causes some yellowing of the leaves and if it gets bad enough, the entire leaf can die. Powdery mildew usually ceases development as the weather turns hot and dry, so treatment isn’t always necessary. However, it should be treated if 20% of the leaf area is infected on the leaf just below the flag leaf and cool, wet weather is predicted to continue.
For a list of fungicides labeled for powdery mildew control in wheat and their rates, take a look at this section of the SC Pest Management Handbook.