Diseases Rearing Their Ugly “Heads” in Small Grain Crops
By Carl A. Bradley, Extension Plant Pathologist
A number of diseases that affect heads of small grain crops have been observed in Kentucky over the last few weeks.
Fusarium Head Blight
One of the “usual suspects” that is no stranger to Kentucky is Fusarium head blight (a.k.a. head scab). Symptoms of Fusarium head blight have been appearing in Kentucky wheat (Figure 1), barley, and rye (Figure 2) fields over the last few weeks. Incidence is varying from low to moderately-high in some cases, depending on the crop, variety, and use of fungicide.
Heads affected by head blight will appear “bleached” in color. Heads often are partially affected, with both healthy green and affected bleached areas present in the same head. In some cases, masses of spores that are salmon-pink in color can be observed on affected heads. Small grain growers may want to evaluate the level of Fusarium head blight in their fields before harvest. It is easiest to observe this disease before heads completely mature.
Growers with moderate to high levels of Fusarium head blight should consider making adjustments to their combine that would allow low test-weight, scabby kernels to be blown out the back of the combine. Research conducted at The Ohio State University indicated that adjusting the combine’s fan speed between 1,375 and 1,475 rpms and shutter opening to 90 mm (3.5 inches) resulted in the lowest discounts that would have been received at the elevator due to low test weight, percent damaged kernels, and level of the mycotoxin deoxynivalenol (DON; vomitoxin) present in the harvested grain (Salgado et al., 2011).
Another disease that is being observed on wheat heads is glume blotch. Glumes of affected heads will turn brown to black in color (Figure 3). In some cases, fruiting structures of the glume blotch fungus may appear on heads. These fruiting structures, known as pycnidia, will look like small black dots, and can be more easily observed with the aid of magnification. Although glume blotch can reduce yield, test weight, and quality, no mycotoxins are associated with this disease.
Finally, I have received a few e-mails and phone calls about loose smut being present in a few fields. Loose smut generally is not considered a major problem of small grain crops in Kentucky, but it can turn into one when “bin-run” seed is planted. Infected plants will produce their heads earlier than non-infected plants (Figure 4). The heads of infected plants will have black spores in place of the grain. These spores will infect developing seeds in neighboring small grain plants.
Infected seeds appear normal, but if planted, will develop plants that have smutty heads. Spores of the loose smut fungus are not toxic, so grain from fields with loose smut can be used for feed and food products, but the seed should not be saved for planting, as this will continue to make the problem worse. Systemic fungicide seed treatments are available that can help manage loose smut problems that can occur with infected seeds.
Salgado, J. D., Wallhead, M., Madden, L. V., and Paul, P. A. 2011. Grain harvesting strategies to minimize grain quality losses due to Fusarium head blight in wheat. Plant Disease 95:1448-1457.