Spores of Alternaria gomphrenae are produced in large numbers on the surface of diseased leaves and other infected plant parts. Cool, moist weather favors spore production by this pathogen. Spores are spread by wind, splashing water and contact with gloves, hands, clothing, etc. Infected floral bracts contaminate seeds, allowing the fungus to move long distances when seeds are sold. Transport of infected plants will also move the pathogen great distances.