Now that most of Pennsylvania has received measurable rain and remains humid, any wheat that is now flowering is at higher risk for infection by Fusarium head blight (also known as scab). Mild, wet environmental conditions promote sporulation of the fungus that causes this disease, and these spores can gain access to the grain head when the plant is flowering (in anthesis). If this happens, the fungus can grow undetected in the kernel and produce mycotoxins, including deoxynivalenol (DON, or vomitoxin).
If your wheat or barley has been experiencing showers or high humidity for a few weeks, consider a fungicide application for scab at early flowering.
Source : psu.edu