Leaves with gray-brown areas surrounded by a dark or yellowish margin are one of the early symptoms of this fungal disease. These discolored areas lack the concentric rings characteristic of early blight, but they may be filled with many small, black spores. Symptoms generally appear on lower leaves first. The fungus can infect a wide variety of plants. In a severe outbreak, septoria leaf spot fungi may also attack seedlings.
The disease is most problematic in cool, wet weather. The fungus overwinters on plant debris in the soil and on weeds such as jimsonweed, horsenettle and nightshade.
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