Honey fungus Armillaria mellea

This fungus belongs to the Basidiomycota group of fungi.

Damage. This fungus primarily attacks trees and shrubs, e.g. apple, lilac and privet. In spring the foliage wilts and turns yellow. Death of the plant may take a few weeks or several years in large trees. Confirming symptoms are the white mycelium, rhizomorphs and toadstools mentioned below (see Figure 15.15).

Rhizomorph Armillaria Mellea
Figure 15.15 Honey fungus. Note the dense clump of honey-coloured toadstools, and also the fungal strands ( rhizomorphs) spreading out from the clump.

Life cycle and spread. The infection process involves rhizomorphs (sometimes referred to as 'bootlaces'), which radiate out underground from infected trees or stumps for a distance of 7 m, to a depth of 0.7 m. The infected stump may remain a serious source of infection for twenty years or more. The rhizomorphs are the only means of spread for this disease. The nutrients they are able to conduct provide the considerable energy required for the infection of the tough, woody roots. Mycelium, moves up the stem beneath the bark to a height of several metres and is visible (when the bark is pulled away) as white sheets, smelling of mushrooms. In autumn, clumps of light-brown toadstools may be produced, often at the base of the stem. The millions of spores produced by the toadstools are not considered to be important in the infection process. Honey fungus often establishes itself in newly planted trees and shrubs that have been planted too deeply. Deep planting produces less vigorous plants that are more vulnerable to infection. Vigour is reduced because feeding roots which ideally should be growing near the surface of the soil have been located in the subsoil.

Control is difficult. Some genera of plants are less likely to be infected (see Table 15.1). Removal of the disease source, the infected stump, is strongly recommended. In large stumps which are hard to remove a surrounding trench is sometimes dug to a depth of 0.7 m to prevent the

Table 15.1 Levels of resistance to Honey fungus in garden shrubs and trees

Plant species

Latin name

Resistance level

Maple

Acer spp.

susceptible

Box elder

Acer negundo

very resistant

Birch

Betula spp.

susceptible

Box

Buxus sempervivans

resistant

Cedar

Cedrus spp.

susceptible

Cypress

Chamaecyparis lawsoniana

susceptible

X Cupressocyparis leylandii

susceptible

Eleagnus

Eleagnus spp.

resistant

Holly

Ilex aquifolium

resistant

Privet

Ligustrum spp.

susceptible

Lonicera

Lonicera nitida

resistant

Mahonia

Mahonia spp.

resistant

Apple

Malus spp.

susceptible

Pine

Pinus

susceptible

Cherry and plum

Prunus spp.

susceptible

Laurel

Prunus laurocerasus

resistant

Rhododendron

Rhododendron

susceptible

Sumach

Rhus typhina

resistant

Lilac

Syringa spp.

susceptible

Tamarisk

Tamarix spp.

resistant

Yew

Taxus baccata

very resistant

progress of rhizomorphs. Loosening soil with a fork and then applying a sterilant, e.g. formalin in a diluted state, may be applied in situations where there are no crops.

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Responses

  • thorsten shuster
    Are mahonia susceptible to honey fungus?
    7 years ago
  • Michael
    Is mahonia susceptible to aphids?
    3 years ago

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