Illinois Extension

Lesions can develop on stems, leaves, and fruit. The characteristic early blight lesion is brown, round or oval in shape, and develops into a series of concentric rings that look like a target or a bulls-eye. Disease symptoms usually start at the base of the plant and work their way up. Various members of the Solanaceae family, including tomato, potato, and weedy nightshades, can be infected.

The disease is caused by at least two species of the Alternaria fungus. Alternaria is often found as a saprophyte (decay organism) on samples, so determining if Alternaria is the cause of the symptoms can be tricky. In the case of early blight, the pathogenic Alternaria species have very long beaks (also called tails) that help distinguish them from saprophytic Alternaria which are shorter and stubbier. The characteristic lesions with the concentric rings can also be used to support this diagnosis.

Management consists of planting resistant varieites (often marked "EB" in catalogs), discarding seeds from infected plants, practicing a 2-year crop rotation out of solanaceous crops, removing weeds to reduce the number of weedy nightshade plants that can act as pathogen reservoirs, watering at the soil line instead of overhead, staking or caging plants to increase air flow, and sanitizing the planting area by removing or burying infected plants especially at the end of the season. Fertilizing with balanced fertilizers to maintain adequate levels of nutrients and encourage vigorous plant growth, and mulching the base of the plants can also be beneficial.