Cause A bacterium, Pseudomonas syringae pv. coronafaciens, carried in seed or overwintered in old oat straw. Moist weather favors the disease. Resistant varieties are available elsewhere, but resistance of varieties common in the Pacific Northwest is unknown.
Symptoms Small, water-soaked spots, surrounded by a light yellow halo, on leaves. Spots are green at first but change to light brown. Lesions may run together. Heavily infected leaves may dry out and die. Occasionally, tiny spots may be found on the hulls.
Cultural control
- Rotate crops and plow under infected straw.
- Do not use contaminated grain for seed.