Fusarium head blight
(FHB), also known as scab, has been reported in irrigated wheat fields in the Columbia Basin. FHB, which also affects barley, is not a new disease to eastern Washington. In fact, FHB is a worldwide problem for wheat and barley production, especially in areas with summer rainfall and warm temperatures (see Return of an Old Problem: Fusarium Head Blight of Small Grains
). FHB is not usually a concern in eastern Washington, however, reports suggest that the disease is becoming more common and increasing in severity.
Symptoms of FHB include completely or partially blighted heads (see photos) due to infection of individual flowers (florets). Several other diseases can cause whiteheads in which the entire stem and head is blighted; however, FHB can be distinguished from them because the stem remains green and only the head is blighted. Under moist conditions, infected flowers and kernels may develop a pinkish color, and kernels become shrunken and shriveled. A distinct line of the pinkish to salmon-orange colored spores are frequently found first along the joint line between the floret and stem. Shriveled kernels can be covered with a white to pinkish fungal growth, and are called tombstone kernels. Later in the season, small, dark-colored fruiting bodies of the pathogen may develop on infected heads. These fruiting bodies contain spores that are spread by wind over long distances.
Concern over FHB is due to direct yield losses associated with the disease and mycotoxins produced in infected grain by the pathogen. Early infection of flowers often prevents kernel formation, whereas later infection results in shriveled kernels. The main toxin produced is deoxynivalenol (DON) and commonly referred to as “vomitoxin” due to its effect on animals that consume infested grain.
There are several different fungi in the genus Fusarium that can cause FHB. These same fungi also cause root and stalk rot of corn, and increasing corn acreage in the Columbia Basin is likely one explanation for the increase in FHB. The FHB fungi survive in corn residue and produce fruiting bodies in the spring that release airborne spores, which can travel long distances and infect wheat plants at flowering and barley after head emergence. Consequently, corn does not have to be part of the rotation in the same field for FHB to be a problem.
Management of FHB includes planting resistant varieties, irrigation management (reduced or no irrigation for a week after flowering), and foliar fungicide applied near heading. (Use only triazole fungicides because strobilurins, whether applied alone or mixed with triazoles, may result in increased DON in seed) It is very important to increase the fan speed on the combine at harvest in those fields with FHB to reduce the percentage of kernels with low test weight and high DON. More information on FHB can be found on the American Phytopathological Society website (Fusarium head blight (FHB) or scab), the University of Idaho Cereals Extension (see Fusarium Head Blight webinar on the front page), and Montana State University extension bulletin.