Celery leaf spot
Small brown spots scattered over celery and celeriac foliage, each one peppered with black pinhead dots that a hand lens shows to be the fungus's fruiting bodies. Those dots are the whole identification: nothing else on a celery leaf carries them, and they separate this from the leaf scorch, spray damage and boron shortage it is usually mistaken for. The disease arrives on the seed rather than from the soil, which puts almost all of the useful action before sowing.
Caused by: Septoria apiicola · also called septoria leaf spot, celery blight, late blight of celery
Nothing available to a home grower will fix this
Once it is established in wet weather there is no fungicide available to a home grower that will stop it, and saying so is more useful than a spray programme that does not exist. The crop is usually still worth eating.
source
GrowingHQ editorial positionhigh confidence
Recorded because the honest answer changes what the reader does with the rest of the season, rather than sending them shopping.
- GrowingHQ editorial synthesis — GrowingHQ
Checked 2026-08-13
What brings it on
Warm wet weather and foliage that stays damp — overhead watering, crowded rows, a wet August. It spreads by rain splash from the lowest leaves upward, so the oldest foliage shows it first and a plant can look sound from above while the base is already covered.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Celery leaf spot
- Cornell Fruit Resources — Cornell University, College of Agriculture and Life Sciences: Septoria leaf spot of celery
Checked 2026-08-13
Usually seen: June, July, August, September
Preventing it
Ordered by how much difference each measure actually makes, not by how often it is repeated.
- Buy seed treated or certified free of the fungus, which is the single control that works — the seed carries it, and untreated home-saved celery seed is the commonest way it arrives in a garden. Failing that, hot-water treatment of seed is the traditional remedy and needs the temperature holding accurately enough that most growers should simply buy fresh seed.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Celery leaf spot — control
Checked 2026-08-13
- Water at the base rather than over the leaves, space plants so air moves between them, and do not follow celery with celery or celeriac on the same ground for at least two years.
source
Horticultural consensusmoderate confidence
- Cornell Fruit Resources — Cornell University, College of Agriculture and Life Sciences: Celery disease management
Checked 2026-08-13
Dealing with it once it is there
- Pick off and bin the spotted lower leaves as they appear — not compost, because the fungus survives on the debris. A crop that is only lightly marked will still produce usable stems; the leaves are the casualty, not the plant.
source
Sourced guidancemoderate confidence
- Royal Horticultural Society: Celery leaf spot — control
Checked 2026-08-13
What it affects
On sprays and treatments
GrowingHQ does not tell anyone what to apply, at what rate, or how often. Pesticide approvals differ by country, change without notice, and the product label is legally binding — it is also the document you are holding. What is described here is cultural and physical control, which is what a home grower can act on without a label in front of them.