Two Tomato Foes: Septoria Leaf Spot and Early Blight

By Nancy Landis, Fairfax Master Gardener
Tomatoes — every gardener’s summer favorite — are as highly favored by plant diseases as they are by humans. One disease that attacks tomatoes during our warm, humid summers is septoria leaf spot. Another is early blight. You will need to be on guard against both in your tomato garden.

Septoria leaf spot on tomato leaves

Septoria leaf spot on tomato leaves

Septoria leaf spot is caused by the fungus Septoria lycopersici. Also known as septoria blight, this disease can affect tomato plants at any stage of development. The symptoms first appear as small circular spots 1/16 to 1/8 inch in diameter, with a water-soaked appearance. They usually start on the undersides of older, lower leaves about the time the plants are setting fruit. The spots may also be seen on stems and other parts of the plant. Gradually, the spots turn gray to tan in the center, with dark brown margins. As the spots grow larger, they may eventually coalesce. The disease spreads from older, lower leaves to younger ones.

The good news: The disease rarely kills the plant, and spots don’t develop on the actual tomato fruit. The bad news: Diseased leaves drop off early, leaving the fruit susceptible to “scalding” from sun exposure. Septoria does not overwinter in the soil, but spores may overwinter on tom