Early Blight Disease in Tomatoes

Leaf Blight

• Early blight disease of tomatoes is caused by the fungus Alternaria solani and displays as a wide number of symptoms over the lifespan of the plant. Fruit rot, collar rot, stem cankers and leaf blight are all potential problems. The first sign of infestation by Alternaria solani is typically the development of 1/2-inch wide lesions on the leaves of the specimen, characterized by concentric circles within the lesion itself. Leaf blight initiates on the lower, more mature leaves before moving up the plant.

Weather

• The leaves of the tomato plant become withered and dry before prematurely falling away, subjecting the fruit to sunscald. Early blight disease normally springs to life during periods of hot and humid weather where the temperature exceeds 80 degrees Fahrenheit and is accompanied by significant rain. The fungus is capable of spreading at a temperature as low as 60 degrees Fahrenheit, provided ample moisture is present. Lesions typically form within two to three days of the initial infection.

Stem Blight

• Early blight disease on tomatoes also affects the stem of the plant, producing symptoms similar to that experienced by the leaves. When stem lesions appear near the soil line, collar rot of the plant is possible along with a girdling -- strangling -- of the plant that denies water and nutrition from traveling upward to the foliage and fruit. As a result, the plant loses vigor, remains small and produces few fruits.

Management

• The fungal lesions may develop on the fruit themselves, growing to significant size on the skin and rotting away the flesh, with heavily damaged fruit dropping to the ground and the remainder largely inedible or not marketable. The disease survives over the course of years through infected vines and litter that remain in the soil. Diseased plants should be removed from the site, crops rotated, and plants widely spaced to allow for excellent air circulation and the drying of moisture from the tomato plant.