Box Blight
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 18°C and 25°C, with humidity above 90%, after rain or heavy dew, while the leaves are still wet. Risk builds after roughly 7 unbroken hours of those conditions, so the morning after such a night is the moment to look.
The signs that lead here
About
Box blight (Calonectria pseudonaviculata) has devastated formal box hedging and topiary across Europe since the 1990s. Warm humid weather and the dense, still air inside a clipped box shape are exactly the conditions it needs, so the tightest, most-prized specimens suffer worst.
Symptoms
Dark brown or black streaks run along young stems, leaves turn straw-brown and drop suddenly, leaving bare patches that spread outwards. In humid weather a white bloom of spores is visible on the underside of infected leaves.
Organic Treatment
Cut out affected growth well past the visible damage, disinfecting the blades between every cut, and bag all clippings and fallen leaves — the spores survive in leaf litter for years. Stop clipping for a season and thin the plant to let air through.
Chemical Treatment
Fungicides only protect; they cannot cure infected wood. Where a treasured specimen justifies it, a preventive programme of tebuconazole or a strobilurin from spring can slow spread, but the disease will return once spraying stops.
Prevention
Clip only in dry weather and never overhead-water box. Space plants for airflow, mulch to stop rain splashing spores up from the soil, and consider replacing badly hit hedges with Ilex crenata or Japanese holly.
Related problems
Box Blight 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.