Sooty Mould
Risk near you, next 48h
See whether your local forecast favours this disease right now.
When it strikes
Watch it before you act
At this level the damage rarely costs the crop. Note the date, check twice a week, and act only if it reaches new growth or the weather turns favourable for it.
Wind-blown spores
Spores travel on air well beyond the affected bed, so a neighbouring garden can be the source. Spacing and airflow matter more than distance from your own infected plant.
It carries over to next season in soil, debris or seed — which is why rotation matters here, not just treatment.
Hot compost only
A heap that reaches and holds 55–65°C throughout will destroy it. A cool corner heap will not, and will return the problem to the beds with the finished compost.
When and where to look
Scout the planting while temperatures hold between 15°C and 30°C, with humidity above 75%.
The signs that lead here
About
Sooty mould is a group of harmless fungi that grow on honeydew — the sugary excretion of aphids, scale insects, whitefly and mealybugs. The mould never infects the plant. It is a symptom with an insect cause, and treating the leaf instead of the insect achieves nothing.
Symptoms
A black, soot-like film coating upper leaf surfaces, stems and anything parked beneath the plant. It rubs off with a wet cloth, leaving healthy green tissue underneath. Heavy coverage shades the leaf enough to slow growth.
Organic Treatment
Deal with the insect: find the honeydew source above the affected leaves and treat it with soft soap, a strong water jet or biological control. Then wash the residue off with warm soapy water, or simply leave it — it weathers away once the honeydew stops.
Chemical Treatment
Fungicides are pointless here. If the honeydew producer needs chemical control, an approved systemic insecticide against that specific pest is the correct product.
Prevention
Watch for ants running up stems — they farm and protect honeydew producers, so a greasy band on the trunk breaks the partnership. Encourage ladybirds and hoverflies, and inspect the undersides of leaves regularly.
Related problems
Sooty Mould 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.