Just what is scab?

Scab, a fungal plant disease, is strikingly described by three Ninth District plant pathologists in the following excerpt from their December 1997 article in the journal Plant Disease.

Edward Lotterman | Agricultural Economist

Published November 1, 1998  | November 1998 issue

Scab can be a devastating disease affecting all classes of wheat and other small grains. This fungal disease, also called Fusarium head blight (FHB) has the ability to completely destroy a potentially high-yielding crop within a few weeks of harvest. Lush, green fields become blighted seemingly overnight. Frequent rainfalls, high humidities, and/or heavy dews that coincide with the flowering and early kernel-fill period of the crop favor infection and development of the disease. Damage from head scab is multifold: reduced yields, discolored, shriveled 'tombstone' kernels, contamination with mycotoxins, and reduction in seed quality. The disease also reduces test weight and lowers market grade. Difficulties in marketing, exporting, and feeding scabby grain are experienced. The fungus persists and multiplies on infected crop residues of small grains and corn. The chaff, light-weight kernels and other infected head debris of wheat and barley, returned to the soil surface during harvest, serve as important sites of overwintering of the fungus. Continued moist weather during the crop growing season favors development of the fungus, and spores are windblown or water-splashed onto the heads of cereal crops. Wheat and barley are particularly susceptible to head infection from the flowering (pollination) period up through the soft dough stage of kernel development.

Mycotoxins are frequently associated with the growth and invasion of cereal grains by scab fungi. The most common toxin associated with Fusarium graminearum-infected grain is vomitoxin. Vomitoxin is known to cause vomiting and feed refusal in non-ruminant animals and poses a threat to other animals and humans if exposure levels are high. The presence of mycotoxins in infected grain further exacerbates the losses that scab can cause.

McMullen, Marcia, Roger Jones and Dale Gallenberg, "Scab of Wheat and Barley: A Re-emerging Disease of Devastating Impact." Plant Disease, Vol. 81, No. 12, December 1997, pp. 1348-1348.