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. Maintain adequate but not excessive soil fertility. A spray program using a recommended fungicide beginning at fruit set and continuing on a 7-14 day schedule should be maintained where early blight problems are anticipated.