Honey fungus: how to recognise and treat it

Disease

Symptoms

Branches die back over several years, or the whole plant dies suddenly in hot dry weather; leaves are smaller and paler, autumn colour comes early, and a last unusually heavy flowering or crop may come just before death.
Peel back the bark at the base — a creamy-white, paper-thin sheet of fungus between bark and wood that smells strongly of mushrooms confirms it; the bark at the base may crack and bleed.
Black or brown root-like cords ("bootlaces") on the roots and in the soil, mostly in the top 15 cm.
Clumps of honey-coloured mushrooms around stumps or over dead roots in late summer and autumn — not every year, and plants may die before any appear.

Dig out and destroy (burn or send to landfill) the infected stump and as many of its roots as possible — this removes the food base the fungus spreads from; do not compost it.
To stop it spreading, bury a vertical barrier of butyl pond liner or heavy plastic 45 cm deep, sticking out 2–3 cm above the soil; regular deep digging also breaks up the bootlaces.
For a valuable infected tree, carefully remove the soil from the base to expose the root flare and keep the trunk base dry — this can slow the rot.

There are no fungicides available to gardeners for honey fungus; chemical control is not possible.

Reference information, not a guarantee. Read and follow the label of any product: dose, safety and the days to wait before harvest.

Where honey fungus is known, do not replant very susceptible plants (privet, lilac, viburnum, thuja, walnut, forsythia, weigela); choose rarely affected ones such as box, bamboos, yew, Chaenomeles or blueberries.
Avoid overwatering and poor drainage, do not let sprinklers wet the base of trunks, and do not plant trees too deep.
Do not use compost containing bootlaces around woody plants.

Figures checked against these sources.