Symptoms and signs of Fusarium head blight (scab) on wheat

Although wheat is typically grown primarily in southern Illinois, where producers are then able plant double crop soybeans, some wheat is also produced throughout the rest of the state. At the Northwestern Illinois Agricultural Research and Demonstration Center (NWIARDC), winter wheat has been included in Dr. Emerson Nafziger long-term tillage and rotation trial since 1996 and more recently has also been planted for Dr. Carl Bradley's research on Fusarium head blight.

Fusarium head blight (FHB), also known as Fusarium head scab, is a devastating disease that can reduce both wheat yield and quality. It is caused by Fusarium fungi including Fusarium graminearum, the same pathogen that causes Gibberrella ear mold and stalk rot in corn. Residue from previously infected wheat or corn plants can be a major source of inoculum. Although infection can take place between head emergence and maturity, infections that take place right after the anthers emerge during flowering can be the most severe. FHB can cause kernels to be small, shrunken and light-weight or may even result in sterility and no kernel at all. Kernels damaged by FHB can be contaminated by mycotoxins produced by the pathogen. Wheat is evaluated at both grain elevators and food processors for one of these toxins, which is known by the nickname vomitoxin. Strict limits are set on the amount of this toxin that can be in both livestock and human food, resulting in severely contaminated loads being docked or rejected at grain elevators.

In their FHB trial, Dr. Bradley's team works hard to create an environment that is favorable for FHB by: planting wheat after corn, applying pathogen-infested sorghum seed and mist irrigation. Environmental conditions this spring have favored widespread FHB development at the NWIARDC – in both the FHB trial AND Dr. Nafziger's trial that relied solely on naturally occurring inoculum and precipitation.

Both symptoms and signs are widespread. Symptoms of FHB include bleached spikelets and small, shrunken kernels (Figures). Signs of the pathogen can be seen with the naked eye and include masses of pink or salmon-colored spores called sporodochia on spikelets and kernels (Figure).

Additional resources

Schmale III, D.G. and G.C. Bergstrom. 2003 . Fusarium head blight in wheat. The Plant Health Instructor. DOI:10.1094/PHI-I-2003-0612-01. Updated 2010.

Wise, K. and Woloshuk, C. 2010. Fusarium Head Blight (Head Scab). Purdue University Extension. Publication BP-33-W.

Bradley, C. 2013. Conditions favorable for Fusarium head blight (scab) in southern Illinois. the Bulletin.