Commonly known as head blight (scab), this fungal disease is present wherever cereal crops are produced. According to Dr. Don Hershman, Extension plant pathologist, University of Kentucky, head scab is the disease most feared by growers of wheat and other cereals, especially barley.
“You can go from having a beautiful-looking crop to a terrible-looking crop almost overnight and, with head blight infection, other diseases begin to creep in,” Hershman says.
The telltale symptom of Fusarium head blight are heads that are partially to completely bleached. This occurs 14-21 days after flowering (anthesis). If flowers in grain spikes are infected just after emergence, kernels that develop will be lightweight and highly shriveled.
Portions of the head that remain unaffected appear green and healthy. Over time, the fungus grows and infects nearby spikelet tissue in the same head; eventually all or most of the head may become diseased. In warm and humid weather conditions, pink-to-orange clusters of spores can be seen at the base of infected spikelets. Eventually, the fungus infects developing kernels, causing them to shrink and wrinkle. Dead, infected kernels, called “tombstones,” are lightweight, discolored and will not germinate if planted.
The Fusarium fungus can produce mycotoxins, which could be harmful to humans and livestock. These mycotoxins are subject to Food and Drug Administration (FDA) regulatory guidance. Growers attempting to sell grain containing mycotoxins, such as deoxynivalenol (DON), may have to settle for a "docked" or reduced price, or suffer outright rejection of the grain at delivery to the elevator. It’s economically important for growers to diligently watch and identify disease symptoms; otherwise, they may not be able to sell their grain.
“Crop protection for head blight begins with variety selection,” Hershman says. “There are no immune varieties, but some varieties are fairly resistant, and growers need to be aware of the disease resistance in the seed they choose.” Crop rotation, residue management, planting multiple varieties with different flowering dates to encourage disease escape, and timely fungicide applications will also help manage head blight and DON.