Tomato plants in many parts of the North America can suffer from this fungal disease, which can appear at any time. Symptoms first appear on oldest, lower leaves. Gray-brown areas have gray centers and a darker border. The dark border lacks the rings typical of early blight. The centers of the discolored areas may have many small, black spores, and sometimes a yellowish area surrounds the darkened areas. It usually slowly defoliates plants, but a harvest is still possible.Prevention and Control
To prevent septoria infection, use copper fungicides such as Bordeaux mixture or liquid copper as directed by the product label, or spray aerated compost tea every 7 to 10 days. Grow ″potato-leaved″ (leaves that have no indentations on the borders) and rugose-leaved tomato varieties (with a puckered leaf surface), which show better resistance.
Photo courtesy Thomas Zitter, Cornell University