Pest Control Library: Bacterial Spot

By National Gardening Association Editors

This disease is found mainly in eastern parts of North America where it affects tomatoes and peppers. Small, dark, corky, raised spots with slightly sunken centers appear on green fruits. Rot organisms may enter at the spots and decay the fruit. Infected blossoms drop; small, dark spots form on leaves, which yellow and drop. This defoliation weakens plants and exposes developing fruits to sunscald. Very warm, wet weather encourages the development of the disease. The fungus overwinters in plant residues in the soil.

Prevention and Control

Use a 3- to 4-year crop rotation. Destroy volunteer tomato and pepper plants and infected fruits. Purchase only certified disease-free transplants. Keep plants well watered and fertilized. Leave plenty of space between plants and support vines to ensure good air circulation. To prevent the disease from spreading, avoid overhead watering and working among plants when they are wet. Apply a fixed copper fungicide as directed by the product label, or spray aerated compost tea every 7 to 10 days while the weather is favorable for disease spread.

Photo courtesy of Howard F. Schwartz, Colorado State University,

This article is a part of our Pest Control Library.

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