Periods of alternating wet and dry weather favor spore dispersal and disease spread. Early blight is often more prevalent on older, senescing tissues and particularly when plants have been predisposed by injury, poor nutrition, insect damage, or other type of stress. Because of the relative resistance of young to intermediate-aged potato plants, major outbreaks of disease do not occur until late in the season. If sufficient moisture is present, spores can germinate and infect tubers. Infection of potato tubers occurs mostly through wounds inflicted during harvest.
Immature tubers are particularly susceptible to infection by A. solani.
Many factors contribute to the effective suppression of early blight. The disease is controlled primarily through the use of resistant cultivars, cultural practices, and foliar fungicides such as chlorothalonil, maneb, triphenyl tin hydroxide and mancozeb. Cultivars with levels of field resistance are available, however no immunity to disease exists in commercial potato cultivars or in their wild parents. Highly susceptible cultivars such as Red Norland, Norchip, and Superior should be avoided in locations where early blight is prevalent and disease pressure is high. Field resistance to foliage infection is associated with plant maturity.