When the spots are abundant, leaves may turn yellow. As the spots enlarge and coalesce, leaves may die from the tip toward the base. The lowest leaves are infected first in early spring, with the disease spreading to the upper leaves as the season progresses. These fruiting bodies, called pseudothecia, become visible in straw and stubble, on and above the soil surface, in late fall and early winter, following the year in which infection occurred. In the early spring, the black fruiting bodies on the old straw and stubble shoot sexual spores called ascospores into the air.
Ascospores are the initial source of spring infections.
The repeating spores, called conidia, develop from the initial infections, which in turn cause additional infections. This cycle of conidial production can be repeated several times during the growing season. Both ascospores and conidia are spread from plant to plant by the wind. Moisture must be present on the leaves for at least six hours at temperatures between 50 and 70 o F for infections to occur. Fungal Diseases Disease prevention by growing resistant varieties is the most economical method of control.