Septoria Leaf Spot on Tomatoes

GardenDraft Team · July 29, 2026 · 5 min read

Part of: Plant Problems & Pest Guides

If your tomato plant is loaded with fruit up top but the lower leaves are turning yellow and dropping, covered in small dark spots, you're probably looking at septoria leaf spot. It's one of the most common tomato diseases, and while it rarely kills a plant outright, it can strip the foliage and weaken the harvest if it climbs unchecked.

How to recognize it

Septoria announces itself as many small, round spots (a sixteenth to an eighth of an inch) with dark borders and tan or gray centers, scattered across the leaves. Look closely and you may see tiny black dots in the centers (the fungus's spore structures). It almost always starts on the lowest, oldest leaves after the plant sets fruit, then moves upward, with affected leaves yellowing and falling. That bottom-up pattern and the many small gray-centered spots distinguish it from early blight, whose larger spots have concentric "bullseye" rings. It hits leaves hardest and, unlike some diseases, usually spares the fruit itself.

Why it spreads, and slowing it down

Septoria is a fungus that overwinters in tomato debris and weeds and spreads when water splashes spores up onto the leaves. So the controls are all about keeping foliage dry and breaking the splash path:

• Remove affected leaves early. At the first spotted lower leaves, snip them off and trash them (not the compost). Removing the bottom foliage slows the climb.
• Mulch. A layer of mulch between soil and plant stops the rain-splash that carries spores up. It is one of the most effective single steps.
• Water at the base, in the morning. Never wet the foliage; let any splashed leaves dry fast. Drip or a soaker hose is ideal — see how often to water.
• Stake and space for airflow. Open, well-supported plants dry quickly. Staking and pruning the lower leaves directly cut the disease's foothold.

Keep it from coming back

Because it overwinters in debris, a thorough fall cleanup — removing every bit of tomato vine and fallen leaf at season's end — denies it a home for next year, and rotating tomatoes away from the same spot (see crop rotation) keeps the soil inoculum from building. Where pressure is heavy, copper or other approved fungicides applied early can slow the spread, but the cultural practices do most of the work. A plant that loses some lower leaves to septoria but keeps its upper canopy will still ripen a full crop — so the goal is to slow it, not to win every spot.