Alternaria alternata f. sp.
Cankers enlarge, girdle the stem before harvest, and kill the plants.
Vascular tissue approximately 2 inches above and below the cankers exhibit brown streaks. The fungus survives on infected tomato debris. Infection occurs when airborne spores land on tomato plants or when plants come in contact with infested soil. Free water is necessary for spore germination and infection. Disease spread is favored by rains, dew, and overhead irrigation.