Honey Fungus (Armillaria Mellea)

Plants/trees Affected

Trees, Shrubs, Woody Plants & some Herbaceous Perennials. Examples are – Lilac, Privet, Apple, Flowering Cherry, Willow, Birch, Walnut, Cedars, Cypress and Monkey Puzzle Trees.

Symptoms

The presence of a white paper-like sheet of mushroom smelling fungus sandwiched between the dead or dying bark and the underlying wood.  Cream/honey coloured mushrooms can be found growing around the base of the infected plant usually in Autumn. Dark or black root like strands (rhizomorphs) often referred to as ‘bootlaces’ also appear beneath the bark and around the roots. These can vary depending on the strain of honey fungus but the most aggressive type tends to have quite slender ‘bootlaces’ which may be difficult to find. The bark can also be loose and come away from the base of the plant, or a resin/gum may ooze from the same area.

Causes

The disease is spread by the root like strands or bootlaces from infected plants penetrating the soil to the root system or collar (where the roots join the stem) of new trees and shrubs. These bootlaces can be found just below the soil surface and grow up to 1m per year. Honey Fungus can also spread when the root system of new plants comes into direct contact with those already infected.

Prevention

Ideal breeding grounds for Honey Fungus are the stumps and roots of dead and decaying trees and so if the site is prone to this disease they should be removed from the garden to avoid an attack.  Vertical barriers to prevent the spread of the fungus can be used, such as a sheet of 50-60 cm deep thick plastic eg pond liner. The best prevention however is to maintain healthy plants by feeding and mulching regularly.  It is also possible to buy species of plants that are more resistant to Honey Fungus than others. Eg Yew, Beech, Hebe and Cornus.

Treatment

• Dig out and destroy infected plants, try to ensure you remove as much of the root system as possible.
• If the fungus attacks hedges it is better to remove not only the affected plant but those on either side as well.
• Do not replant with woody species on the site where there has been an attack for at least one year and when replanting choose trees/shrubs which are resistant to Honey Fungus or non-woody species.