How to identify septoria leaf spot on tomato plants
At first, it’s just a few speckled leaves near the bottom of the plant — nothing to worry about, right? But soon, tan-to-gray circular spots spread, leaves turn yellow and drop, and your once-lush tomato plant starts to look bare as it struggles to produce fruit.
What causes it
Septoria leaf spot is caused by the fungus Septoria lycopersici, which infects the leaves, not fruit, of tomato plants. As the disease progresses, it moves upward, weakening the plant and reducing fruit production. The fungus thrives in warm, humid conditions and spreads when rain or overhead watering splashes fungal spores from infected soil or plant debris onto lower leaves. Insects, garden tools or even your shoes or pant legs can carry the infection from plant to plant.
How to solve septoria leaf spot
- Good airflow is key: Follow recommended spacing guidelines, and stake or cage tomatoes to improve circulation.
- Keep leaves dry by watering at the base of the plant and pruning lower leaves to prevent contact with the soil.
- Adding a layer of mulch helps prevent spores from splashing onto foliage during rain.
- At the first sign of infection, remove affected leaves immediately to slow the spread.
- At the end of the season, clean up all plant debris and rotate crops to prevent spores from overwintering in the soil.
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