September 3, 2008

Fusarium head blight or scab of wheat has occurred in Nebraska during the last two growing seasons because of excessively wet weather before and during flowering. In both years south central and eastern Nebraska were affected the most. For details on the disease and how to manage it, see EC1896, Fusarium Head Blight of Wheat. Losses from scab are manifested as low yield, poor quality grain, discounts at the elevator due to the toxin deoxynivalenol (DON, vomitoxin) in affected grain, and low germination and seedling blights if affected grain is used as seed. This article highlights strategies that can be used this fall to reduce losses from scab.

Seed Cleaning And Fungicide Seed Treatment

Plant certified, fungicide-treated wheat seed this fall. If scab-affected grain needs to be used as seed, thoroughly clean it to remove scabby grain and treat it with a fungicide. Treating seed with fungicide will increase germination and prevent or reduce seedling blights caused by the scab fungus, but it will not stop scab from developing on wheat heads the following spring. For a partial list of fungicide seed treatments, see the August 8 Crop Watch article, Seed Fungicides Offer Early Protection for 2009 Wheat Crop.

Crop Rotation Sequence

The scab fungus survives mainly on corn and wheat residue, but also can survive on residue of other grasses. If possible, don't plant wheat after corn or wheat. While planting wheat after corn or wheat would not necessarily result in scab, if the disease were to occur due to favorable environmental conditions, the damage likely would be greater than if wheat were planted after a broadleaf crop such as soybean. It should be noted that when environmental conditions are favorable for scab development, some level of disease will occur regardless of rotation sequence. This is because spores of the scab fungus become airborne and can be blown from field to field.

Cultivar Selection

Although no wheat cultivars have even moderate resistance to scab, some cultivars have a minimal level of resistance or tolerance to the disease. Studies have shown that cultivars differ in their susceptibility to scab as well as to DON accumulation. Cultivars that are highly susceptible to scab and DON should be avoided. Table I shows overall scab intensity (scab index) and DON levels in the 2008 State Variety Trial in Saline County. Table II shows overall scab intensity, Fusarium-damaged kernels (commonly known as FDK), and DON levels among 12 cultivars evaluated in 2008 at the Agricultural Research and Development Center near Mead. The higher the scab index, the more susceptible a cultivar is. Note from Tables I and II that a cultivar with a low scab index can have a high level of DON and vice versa. When selecting cultivars, consider susceptibility to both scab and DON. Grain with a DON concentration greater than 2 ppm is usually discounted at the elevator.

Flowering Dates

Spores of the scab fungus infect wheat heads mostly during flowering. Planting several cultivars that differ in flowering dates increases the probability that some cultivars will escape infections, reducing the likelihood of overall loss from scab.

Stephen Wegulo, Extension Plant Pathologist
Lenis Nelson, Extension Crop Variety Specialist
John Hernandez Nopsa, Graduate Student
Julie Breathnach, Research Technologist