Crown rust, caused by the fungus Puccinia coronata is one of the most destructive diseases of oats. It is recognized by flaky red pustules on the leaves, and it is similar to leaf rust of wheat. Because crown rust can develop rapidly when environmental conditions are favorable, it can cause serious yield losses. Varietal resistance is the primary means of control, but fungicides may be effective when rust is severe. Helminthosporium leaf blotch, caused by the fungus Drechslera avenae, attacks both leaves and kernels.
Diseased kernels turn brown at the basal stem.
By attacking the leaves, photosynthesis will be reduced, resulting in light and shriveled kernels. This happens also by direct attack of the fungus on the kernels. Crop rotation, variety choice, and fungicide treatment on the seed will reduce this disease. Loose smut, caused by the fungus Ustilago avenae, causes blackened heads similar to that of loose smut of wheat and barley. It is controlled by carboxin seed treatment and resistant varieties.