What is honey fungus and can I save my plants?

Honey fungus is over-diagnosed. Most sudden shrub deaths in gardens are drought, waterlogging, root damage or vine weevil. Confirming it matters, because the management response is drastic and there is no reason to take it on the basis of a guess.

What you'll need

• Spade
• Knife or chisel
• Gloves

Step by step

1. Look under the bark at the base.Cut or peel a patch of bark away just above ground level. A sheet of creamy-white fungal growth smelling strongly of mushrooms is the definitive sign.
2. Dig for bootlaces.Black or dark brown strands like bootlaces, running through the soil or under the bark. Fresh ones snap and are white inside.
3. Look for toadstools in autumn.Honey-coloured toadstools in clumps at the base of the affected plant in autumn. They are a supporting sign rather than proof on their own.
4. Rule out the alternatives first.Drought, waterlogging, root damage from building work, vine weevil and phytophthora all cause similar sudden decline. Check the soil, check the roots for grubs, and check what has changed nearby.
5. Accept there is no chemical control.Nothing available to gardeners treats honey fungus. Products claiming to do so do not work, and the fungus lives on dead wood in the soil regardless.
6. Remove infected plants and as much root as you can.The fungus feeds on the dead root system left behind, so grubbing out the stump and major roots reduces the food supply and slows spread.
7. Remove buried wood and old stumps.Old stumps, buried timber, dead roots from previous planting — all of it feeds the fungus. Clearing them is the most useful thing you can do.
8. Consider a physical barrier.A vertical butyl or heavy plastic barrier 450mm deep sunk into the soil can slow the spread of rhizomorphs to a valued area. It is a delaying tactic, not a cure.
9. Replant with more resistant species.Yew, box, beech, hornbeam, holly, bamboo, cotinus, ceanothus and most conifers other than cypress show reasonable resistance. Never plant a known susceptible species back into an infected spot.
10. Keep everything else growing strongly.Vigorous, well-watered, unstressed plants resist infection far better. Mulch, water in drought and avoid root damage.

Tips

• White sheets under the bark plus black bootlaces in the soil. Anything less is not a diagnosis.
• There is no chemical control. Anything sold as one does not work.
• Removing old stumps and buried wood does more than anything else you can do.

Common mistakes

• Assuming honey fungus from a sudden plant death — Drought, waterlogging and root damage kill far more shrubs than honey fungus does. Confirm with the bark and the bootlaces before taking drastic action.
• Leaving the stump and roots in the ground — The dead root system is exactly what the fungus feeds on and spreads from. Grubbing it out is the single most effective control measure available.

If it doesn't work

Questions people ask