Phytophthora root and foot rot

Phytophthora

also called root and foot rot, phytophthora root rot

A waterborne rot of woody plants that kills from the roots up: the whole plant fades and wilts, and the bark at the base is stained rusty-brown beneath.

Water mold No cure Soil-borneSpread in waterRain splash Spreads to neighbors

What you'll see

Slice the bark at the base of the stem and the wood beneath is stained orange- to rust-brown, often with a sharp line between healthy cream and dead tissue.
The whole plant looks starved — leaves small, pale, sparse — then wilts even though the soil is wet.
Foliage yellows, browns and dies back branch by branch, and the plant fails to come away in spring.
Roots are black, sparse and brittle, with the fine feeder roots rotted away.
A dark, sometimes weeping stain may run up from soil level on the trunk.

Why it happens

A group of fungus-like water molds that swim through wet soil as swimming spores and attack the roots and stem base. They arrive in contaminated soil, on infected nursery stock or in water drawn from a pond or butt.

Waterlogged, badly drained or over-watered ground is the trigger; warm wet soil lets the spores swim to fresh roots. Plants in heavy clay, low spots or pots stood in saucers are most at risk.

Treating it

There is no cure once the roots and stem base are rotted; lift and destroy a collapsed plant, and do not compost it.
Catch it very early on a valued plant by easing the soil off the crown, improving drainage and letting the base dry out.
Remove soil from around the buried collar if it has been planted too deep.
Do not replant a susceptible woody plant in the same spot — the spores linger in the soil.

Keeping it away

Plant on free-draining ground and never bury the stem base below its original soil mark.
Improve heavy soil with grit and organic matter, or plant on a raised mound in wet sites.
Water carefully and never leave pots standing in trays of water.
Use mains or stored rainwater kept clean, not stagnant water, on vulnerable young plants.
Buy healthy stock from a reputable source and reject any with dark, rotten roots.

Who gets it

A wide range of woody plants — especially rhododendron, yew, lawson cypress, apple, cherry, beech and many container shrubs.

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