Armillaria mellea - Honey Fungus, Boot-lace Fungus

Scientific name: Armillaria mellea

Common name: Honey Fungus, Boot-lace Fungus

Type of decay: White rot in the heartwood. Also kills cambium (sapwood rot)

Description

Armillaria mellea is one of seven species of Armillaria found in the UK. The fruiting bodies appear from September-November most commonly in groups but also singularly. The toadstools are round and button-like when young, becoming flatter with age. They are honey-yellow to brown on top with creamy brown stems. There is a distinctive white collar just below the cap. Spore powder is white. On host trees and shrubs infected with Honey fungus a white sheet can often be seen just beneath the bark or around the roots. This is a mass of hyphae known as mycelium. Also found in the soil and around infected roots are boot-lace like strands known as rhizomorphs. These are red-brown when young becoming black and brittle with age. Rhizomorphs are strands of hyphae that are used to spread through the soil and attach to the roots of hosts.

Effects of fungus on tree

Rhizomorphs attach themselves to the roots and under the bark of infected trees. Nutrients are then absorbed from the woody tissue of the host, eventually leading to death. The wood of an infected tree often has a yellow-brown discolouration. The wood becomes soft and with loss of lignified strength can fail. The decay can form a cavity within the stem. Softening of the root structure can cause ductile fractures of the root plate leading to windthrow. Heartwood decay can also lead to stem failure however this is less common.

Hosts: Broadleaf trees and conifers including: birch, cedar, cypress, walnut, apple, pine, spruce, willow, rhododendron, cherry, plum and more.