Septoria Leaf Spot
Risk near you, next 48h
See whether your local forecast favours this disease right now.
When it strikes
Treat, then re-check in 5–7 days
Pick off the worst material, apply the organic option below, and look again after five to seven days. If the spread continued, escalate rather than repeating the same treatment.
Rain and irrigation splash
Water splashing off soil and infected leaves carries it upward and along the row. Watering at the base and mulching the soil surface break the route.
It carries over to next season in soil, debris or seed — which is why rotation matters here, not just treatment.
Keep out of the compost
This survives a garden heap. Bag it for municipal green waste, which is composted industrially at temperatures a garden heap cannot reach, or burn it where that is permitted.
When and where to look
Scout the planting while temperatures hold between 20°C and 26°C, with humidity above 90%, after rain or heavy dew, while the leaves are still wet. Risk builds after roughly 8 unbroken hours of those conditions, so the morning after such a night is the moment to look.
Rule these out first
Same category, and at least one host crop in common — so they are genuinely confusable in the same part of the garden.
The signs that lead here
Full problem lists for these crops
About
Septoria leaf spot (Septoria lycopersici) is a major tomato disease in humid summers, causing heavy defoliation from the bottom up that exposes fruit and slashes yield.
Symptoms
Many small circular spots with dark borders and pale grey centres, often dotted with tiny black fruiting bodies, starting on the lowest leaves after fruit set.
Organic Treatment
Strip infected lower leaves, mulch heavily, and spray copper or chlorothalonil at first symptoms. Improve airflow with staking and pruning.
Chemical Treatment
Chlorothalonil or mancozeb every 7–10 days, alternating with azoxystrobin in severe seasons.
Prevention
Rotate away from tomatoes for 2 years, mulch, stake, water at the base, and remove debris at season end.
Crops at risk
Related problems
Septoria Leaf Spot risk by location
Each location has a month-by-month profile computed from the weather archive: how many hours a year actually meet this disease’s thresholds.