Cause The bacterium, Pseudomonas syringae pv. syringae, causes a disease favored by cool to mild temperatures (59°F to 77°F) and high relative humidity. The bacterium is in seeds, soil, plant residues, and water and may spread by infected seed or water. Severe epidemics are periodic in irrigated wheat. Other cereals may be affected, including oats, rye, and triticale.
Symptoms Generally after boot stage, water-soaked spots develop, which expand and progress from gray-green to tan-white. Spots may coalesce into irregular streaks or blotches, and entire leaves may turn brown and die while heads and glumes remain symptomless. Slimy droplets may develop on leaves in wet weather.
Cultural control Bacterial diseases are difficult to control once symptoms are evident in the field.
- The best control is to avoid the disease by planting pathogen-free seed.
- Irrigate less frequently to keep relative humidity lower.
- Avoid overhead irrigation when possible.