Corn Smut
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.
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 26°C and 34°C, in dry air below 60%.
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
Corn smut (Ustilago maydis) infects sweetcorn through wounds and through the silks during hot, dry weather following a wet spell. In Mexico the swollen galls are the delicacy huitlacoche; in a European garden they are simply a lost cob.
Symptoms
Silvery-white swollen galls on cobs, tassels, stems or leaves, which enlarge, darken and finally rupture to release a mass of powdery black spores. Infected plants may also be stunted or distorted.
Organic Treatment
Cut the galls off while still firm and white, before they burst, and bag them — once they rupture the spores go into the soil for years. Do not compost infected material.
Chemical Treatment
No effective fungicide exists for garden use, and seed treatments do not prevent it because infection is local and airborne, not seed-borne.
Prevention
Avoid mechanical damage during hoeing and detasselling, keep the crop evenly watered in hot weather, do not over-apply nitrogen, and rotate the block. Some modern varieties carry useful partial resistance.
Crops at risk
Related problems
Corn Smut 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.