Early Blight Information

Early Blight Information

By Kat Yares, Garden Guides Contributor

About Early Blight

Early blight, Alternaria solani, is a fungus that affects potato and tomato crops across the North American continent. Dark rings form lesions on the older leaves of the plant first, and the leaf will yellow and die. Early blight can spread to the tubers of the potato plant and can spread to the fruit of the tomato plant. Early blight thrives in high humidity and warm temperatures.

Prevention and Control

Plant resistant varieties in well-drained soil. Copper-based fungicides work well but should be used sparingly, as the copper can be toxic to microbes and earthworms in the soil beneath the plants. Water the ground area around the plants if needed but avoid watering the leafy portions of the plant.

Affected Plants

Tomato and potato plants


Left untreated, early blight can destroy an entire crop of either tomatoes or potatoes. If early blight affects tomato plants after fruits are mature, the fruits can still be harvested.

Other Methods of Control

Rotate crops yearly and do not allow either potato or tomato plants to grow in a garden area for at least three years. Fertilize the soil before planting with a good compost mixture to ensure healthy plants. Plant wide rows to minimize spore travel from row to row of plants.

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