The fungus overwinters on the seed or crop residue. Spores are produced and spread by wind and rain. Spores produced on infected plants are mainly responsible for destructive, secondary spread of the disease within the crop. Spore production and infection of the growing crop is favoured by high relative humidity and temperatures around 20 degrees Celsius. Damage Description Light brown spots with distinctive dark brown net-like patterns appear on the leaves, sheaths and glumes.
Spots enlarge and join into dark brown stripes.
There is also a spot-producing form of this fungus that produces dark brown spots surrounded by a yellow zone. Symptoms vary with the variety and weather. Yield loss is proportional to the amount of leaf area destroyed on the upper two leaves. The average yield loss in Alberta is about 1.5 per cent. Losses of 50 per cent and more have occurred in highly susceptible varieties such as Elrose.