Dark brown cankers may develop on and girdle stems of seedlings at the soil line. Stem lesions on older plants usually remain confined to one side of the stem. Leaf symptoms appear on older leaves first and are characteristic of the disease. The leaf area surrounding these spots usually turns yellow. Infected leaves eventually turn brown and drop from the plant.
Defoliation progresses upward from the lower plant.
The fungus survives in the soil by forming resistant spores in association with diseased tomato debris that are capable of persisting for one year and probably longer. Infection occurs rapidly under warm, humid conditions. Thousands of spores are produced in spots of infected leaves that are capable of causing more infections. Plants under stress from nitrogen deficiency, heavy fruit load, or other factors are most susceptible to the disease. Avoid prolonged wetting of leaves from irrigation or use drip irrigation.