Plant Diseases: Alternaria Blight (Early Blight, Tomatoes)
Blight disease plant symptoms are generally defined as general killing of leaves, flowers and stems. Tomatoes grown in outdoor and greenhouse plantings are very susceptible to Early Blight caused by the Alternaria fungus. Symptoms which are first seen on leaves are dark brown, circular to oval spots, marked by concentric rings in a target pattern. These spots first appear on lower, shaded foliage, with spots growing together to blight a large portions or all of leaves. Cankers may form on older stems and blossom-drop may occur with loss of fruit. Blighted leaves are dark brown and die with foliage dying from the bottom of the plants upward. The dying leaves of course greatly reduce tomato fruit production. Early blight (Alternaria blight) is the most common disease of tomatoes in the Central and Atlantic United States.
The Alternaria fungus over-winters in infected plant debris and can survive in the soil as long as the refuse is not completely rotted. It also over-winters on seed and on weeds. Therefore, garden sanitation is important in early blight prevention. The fungus enters tomato plants through wounds and thrives during warm (optimum temperature of 85 F ) and moist conditions, including frequent rains, plant watering and heavy dews. Once the fungal spores are formed on infected plants, the spores are spread by wind, splashing rain, and on tools. Early blight can be controlled by using a good broad spectrum fungicide, such as GreenCure®, and spraying every 2 weeks during periods of optimum conditions for the Early Blight disease.