Wet, humid conditions make fusarium head blight a concern for wheat 

After praying for the moisture to carry the High Plains wheat crop through to an abundant harvest, some have received more rainfall than they bargained for, leading to a significant risk of fusarium head blight. This disease is caused by the fungus Fusarium graminearum. 

“Fusarium head blight, or head scab, is the most damaging wheat disease in the U.S,” said Meriem Aoun, Oklahoma State University small grains pathologist. “Yield losses occur because infected kernels are shriveled or do not develop at all. The yield losses vary depending on the disease severity and the variety susceptibility level.” 

Aoun said FHB is a major problem in the northern and eastern regions of the United States and it can rear its head in states, like Colorado, Kansas and Nebraska, if conditions are right.  

For Oklahoma, the disease is uncommon but occasionally occurs in eastern Oklahoma where the rainfall totals are more significant. Most Oklahoma wheat producers are not used to managing FBH and do not usually plant varieties that are resistant to the disease. 

The uncommonly wet, warm and humid conditions parts of the High Plains have been experiencing in April have led to increased susceptibility to FHB. Aoun said these environmental conditions occurring at the flowering stage have put the crop at an increased risk of infection. 

“Infected wheat heads have a bleached appearance that could be accompanied by a salmon-pink discoloration indicative of FHB fungus growth and sporulation,” she said. “Infected kernels, known as tombstones, become shriveled, chalky, and white to pink in color.” 

Susceptibility and risk of FHB

FHB affects wheat and other cereals and is most common in wheat fields planted after corn. 

“If the FHB risk is high and the grown variety is susceptible, fungicide application should be made,” Aoun said. “The timing window is narrow for applying fungicides that suppress FHB. The best fungicide application is at the early flowering stage. Applying fungicides earlier, at heading stage, will not effectively manage FHB. However, some studies showed that delaying application five to seven days after the start of flowering can still suppress FHB.” 

Aside from reducing yield, FHB can also produce mycotoxins harmful to humans and livestock. 

“FHB fungus produces mycotoxins such as deoxynivalenol, which contaminates grain,” Aoun said. “Elevated concentrations of DON can lead to price discounts or rejection. Tombstones have high levels of DON, but they are usually discarded with chaff during harvest. However, asymptomatic kernels can still have high DON concentrations.” 

Aoun said the fungus can overwinter on the crop residue, which will serve as the primary inoculum for the coming season. Since it is most common in wheat fields planted after corn, she recommends producers avoid planting wheat after corn, if possible, or plant resistant varieties.  

To assess individual risk, producers can use a web-based model found at www.wheatscab.psu.edu/. This website uses weather data to predict the risk of FHB for a given area across the U.S. The tool guides growers in fungicide application decisions. 

Lacey Vilhauer can be reached at 620-227-1871 or [email protected].