this pathogen needs cool, moist conditions, and development occurs more quickly as plant tissues age. an increase in severity of infection is often noted when the crop canopy closes due to the dense growth that prevents dry air from penetrating the canopy. this creates a cool, humid, moist environment under the canopy, and as a result, the disease symptoms are most prevalent at the base of the canopy and spread up the plant. plant lodging also creates a dense, humid environment favorable for the pathogen. the optimal temperature for disease establishment and development is around 20c. spore dispersal and the development of the disease are slowed in the absence of high levels of moisture.