The disease is favored by cool, wet weather. Wind and rain spread the bacteria from plant to plant as well as to different parts of the same plant. Insects may play an important role in spreading halo blight bacteria. Halo blight is not normally a serious disease of oats. If control measures are needed, crop rotation, plowing under crop debris, and using certified seed should lessen disease.
Symptoms appear as small, water-soaked lesions on leaves.
These lesions may coalesce into stripes or blotches, which may extend the length of the leaf blade. These stripes often have narrow, yellowish margins. As the stripes age they turn a translucent rusty brown. The bacterium is seedborne and can survive in infected crop stubble for up to 2 years. During periods of cool wet weather, the bacteria are blown or splashed onto leaves.