Phytophthora Root Rot
Risk near you, next 48h
See whether your local forecast favours this disease right now.
When it strikes
Remove affected material now
Take out the affected leaves, shoots or whole plants before the next wet spell, bag them as you cut, and wash your hands and tools before touching healthy plants.
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 15°C and 30°C, with humidity above 90%, after rain or heavy dew, while the leaves are still wet. Risk builds after roughly 24 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
Phytophthora is a water mould rather than a true fungus, and it swims: its spores move through waterlogged soil to find roots. It kills more garden shrubs and trees than any other soil pathogen, and almost every case starts with drainage, not infection.
Symptoms
Leaves are small, pale and sparse, and the plant wilts in warm weather despite wet soil. Whole branches die back one at a time. Cut the bark at the base and the tissue underneath is brown or reddish instead of white-green, often with a sharp line between healthy and dead.
Organic Treatment
There is no cure for a plant this far gone. Remove and destroy affected plants with as much root as you can, improve drainage before replanting, and switch to raised beds or mounds where the water table is high.
Chemical Treatment
Phosphonate (potassium phosphite) treatments boost a plant’s own defences and can hold back mild infections in valuable specimens. Metalaxyl-based products exist commercially but do not restore rotted roots.
Prevention
Never plant into a hole that holds water. Plant slightly proud of the surrounding soil, avoid piling mulch against stems, do not overwater established shrubs, and buy plants only from nurseries with clean stock.
Crops at risk
Related problems
Phytophthora Root Rot 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.