Issue No. 5, Article 7/April 23, 2004
Fusarium Head Blight (Scab) of Wheat, Part 1: The Disease
By many reports, the wheat crop is doing well in Illinois at this date. Various problems are being reported, but overall the wheat came through the winter well and shows promise for good yields again this year. We all know, however, that much can happen to damage the wheat crop between now and harvest. Several viral disease problems of wheat were described in an article in the Bulletin last week. This article covers basic characteristics and management of Fusarium head blight, one of the most important diseases of wheat in Illinois.
Fusarium head blight (FHB), also called head scab, was a major problem that affected the wheat crop in the southern half of Illinois last year. Although this disease causes its major problems when wheat begins to head, it is important to understand this problem and the options for disease management. FHB can be a destructive disease of wheat anywhere in Illinois. The disease can reduce yields and market grade and can reduce quality through production of the mycotoxin deoxnavalinol (also called DON, or vomitoxin) in the grain. Last year, by some estimates, the greatest effect of FHB in Illinois was on reducing grain prices from many fields in southern Illinois due to excessive amounts of DON.
FHB is caused by the fungal pathogen Fusarium graminearum. Another form of the same pathogen causes Gibberella stalk and ear rot of corn. This fungus, which overwinters on wheat, corn, and grass residues, is favored by large amounts of corn or wheat residue on the soil surface. Spores from these sources are spread by wind and rain to wheat heads, where infection occurs during flowering when weather is wet and warm. Symptoms can develop within 3 to 4 days after infection, when temperatures are favorable for infection (70°-85°F).
FHB thus has a narrow time frame for infection only at flowering, and only when conditions are warm, humid, and wet. The symptom of FHB that is easiest to recognize is premature bleaching of several or all spikelets on a head of wheat. Orange masses of spores or small black specks may also develop at the base of infected spikelets. The fungus can produce high levels of DON in heads that do not appear to be heavily infected. Fusarium head blight can be managed in part by rotating away from corn and wheat for at least 1 year and choosing cultivars with tolerance to the disease. In 2004, the fungicide Folicur has also been temporarily approved for restricted use to manage FHB of wheat in Illinois. (See the following article for more information on Folicur and how it can be used as part of an integrated system to manage FHB if weather conditions become favorable for development of this disease.)--Dean Malvick
Fusarium head blight symptoms on wheat.