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HONEY FUNGUS - Armillaria spp

"Honey Fungus" is a term that is likely to cause most gardeners a lot of (often unnecessary) heartache. There are six species endemic in this country, but only two will cause damage to living plants, the rest need dead and decaying woody matter to thrive.

Have I got honey fungus?

On the plant, clear away some soil round the base. Peel back the bark where the roots and stem join; sheets of white or creamy cream coloured fungus indicate the possible presence of honey fungus, particularly if the bark is softy and black. This is the best indicator of honey-fungus.

In the soil, look for black bootlace-like threads. Properly called rhizomorphs, and living only in the top 30cms of the soil, these are one of the fungus’ ways of spreading from plant to plant. If you find a large mass of these near a compost heap, they almost certainly belong to Armillaria gallica w(which will sometimes attack and kill plants that are already under stress, eg during a drought). The rhizomorphs help to break down organic matter in the soil.

Toadstools. Honey-coloured toadstools may appear on the autumn around the base of some infected plants or stumps in the autumn. It pays to clear these away as they produce spores which carry the infection. Although these are edible, you must be very certain that these are honey-fungus toadstools before you tuck in.

Can I get rid of honey fungus?

No. There is no chemical control available.

How do I control honey fungus?

First of all, remove all infected plants, including as much of the roots as possible. Where susceptible plants are close together it may pay to remove plants on either side of the infected plants. Plants that are growing vigorously and well are much less likely to be infected, as armillaria is a weak competitor. Make sure that new plants are adequately watered and mulched.

Almost all plants have a certain resistance to honey-fungus. Avoid those that are particularly susceptible, and choose from those that are more strongly resistant (see the two lists below).

Plants that are more strongly resistant to honey fungus:

  • Abutilon
  • Acer negundo
  • Actinidia
  • Ailanthus altissima
  • Bamboos
  • Buxus sempervirens
  • Carpenteria
  • Carpinus
  • Catalpa
  • Celastrus
  • Cercis
  • Ceratostigma
  • Chaenomeles
  • Choisya
  • Clematis
  • Cotinus
  • Crataegus
  • Elaeagnus
  • Fagus
  • Fothergilla
  • Hebe
  • Ilex
  • Juglans regia
  • Juniperus
  • Larix
  • Lavandula
  • Liquidambar
  • Malva
  • Nothofagus
  • Passiflora
  • Phlomis
  • Photinia
  • Pieris
  • Pittosporum
  • Platanus x hispanica
  • Quercus
  • Rhus
  • Robinia
  • Sarcococca
  • Tamarix
  • Taxus
  • Tilia

Plants highly susceptible to honey fungus:

  • Araucaria
  • Betula
  • Cedrus
  • Chamaecyparis
  • Cotoneaster
  • X cupressocyparis leylandii
  • Forsythia
  • Hydrangea
  • Juglans regia
  • Ligustrum
  • Malus
  • Paeonia
  • Prunus
  • Rhodendron
  • Ribes
  • Rosa
  • Salix
  • Syringa
  • Wisteria