Armillaria Root Rot – The Root of All Evil

Introduction:

Armillaria Root Rot is one of the most common root diseases that affects garden trees and shrubs and is caused by Honey fungus (Armillaria x). There are many species of Honey fungus, several of which cause the deadly root rot due to having parasitic qualities. Some of the species include Armillaria mellea and Armillaria ostoyae.

Identification:

When checking if your tree has been infected with Honey Fungus you should peel away the bark at its base. If there is a creamy to white layer of mycelium (fungal tissue), then the tree has been infected. Rhizomorphs also form on the roots of the tree. Mycelium and rhizomorphs are present all-year-round, whereas toadstools (which also may identify that your tree is infected) appear in the late summer to autumn and are a honey colour. You will also be able to detect infection above-ground as branches may begin to die back, small and paler leaves may form, there may be premature autumnal colour or bark may experience cracking and bleeding at its base.

Susceptible Trees

Some plants have a stronger resistance to the disease, including the Box Elder (Acer negundo). Whereas others are more susceptible; e.g. Beech, Birch and Apple. 

Click here for our downloadable list of susceptible vs non-susceptible species. Tolerant and Less Tolerant Species of Armillaria Root Rot

Habitat:

Predominantly, Honey fungus forms on roots, trunks and stumps. Rhizomorphs thrive in moist soil, just below the surface, but can also develop deeper in dry soils. Typically, wooded areas and gardens are the most affected.

Spread and Reproduction:

Infected trees develop rhizomorphs which protrude from its roots. These then spread underground and attacks further roots of trees in turn, killing them and decaying its wood.