Powdery mildew on oat leaves caused by Erysiphe graminis avenae . Loose smut on oat heads, caused by Ustilago avenae . The use of resistant varieties and fungicide seed dressings tends to keep this disease in check. However, loose smut has the potential to cause significant yield losses if control measures are not followed. Oat heads infected with the loose smut fungus are brownish black in color as compared to the normal green color of healthy heads.
Infected spikelets become masses of black spores surrounded by a delicate, white membrane.
This membrane soon ruptures, releasing the spores. Usually all heads on an infected plant are smutted. It is difficult to distinguish healthy from diseased plants before heading out. Diseased plants are often overlooked at harvest because they are shorter than healthy plants and by this time they have lost their mass of spores. The spores of the loose smut fungus are spread mainly by wind.