Leaf diseases may range in severity from small, unimportant spots to large lesions that prematurely destroy large areas of the leaves. The relative severity of leaf infections often varies with weather conditions. Leaf rust is seen as small, yellow-orange pustules on leaves and sheaths. Heavily infected leaves die prematurely, reducing kernel size and number. Early barley varieties generally escape serious rust attacks.
Powdery mildew is a common disease of barley.
The fungus forms white to light gray powdery growth on the leaves, sheaths, stems and glumes. In heavy infections, powdery mildew can cause premature death of leaves, especially lower leaves. No varieties adapted to Missouri have resistance, but in most years the disease is not serious. Net blotch is a common fungus disease of the leaves. It can be quite serious in seasons of high moisture.