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Identifying and Controlling Septoria Leaf Spot of Tomato

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What is Septoria Leaf Spot?
Tomato Septoria Leaf Spot

Septoria leaf spot starts out as small brownish circles on the undersides of the lower leaves.

Photo: William M. Brown Jr., Bugwood.org
Septoria leaf spot, also called Septoria blight, is a very common disease of tomatoes. It is caused by a fungus (Septoria lycopersici) and can affect tomatoes and other plants in the Solanaceae family, especially potatoes and eggplant, just about anywhere in the world.

Although Septoria leaf spot is not necessarily fatal for your tomato plants, it spreads rapidly and can quickly defoliate and weaken the plants, rendering them unable to bear fruit to maturity.

Causes

Fungus spores are very good at hiding out and waiting for ideal conditions. They can travel great distances, in hopes of finding those conditions. The Septoria lycopersici fungus lives on the fallen tomato plant debris and weeds on and in the soil. It is spread to the plants by both water and wind, usually splashing up on the plants from the soil. Warm (60 - 80 F.), damp conditions are the most favorable for Septoria leaf spot to develop and that's when you should be most watchful. If caught early, it can be controlled. Read on for photos and descriptions of Septoria's symptoms.

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