Naturally Trees - Expert Arborcultural Planning, Advice and Care Since 1998

Armillaria root rot

by Andrew Scales | May 4, 2010
Armillaria root rot



Why am I finding mushrooms in my garden and are they harmful to my trees?

It’s that time of year again when we start to notice mushrooms appearing in our gardens!

Between April and June when temperatures start to cool, you should look for mushrooms growing within your garden. Although most of these fruiting bodies are harmless to plants there is one in particular that is detrimental to trees.

Armillaria root rot has a wide host range and can be found on over 250 plant species including Eucalyptus, Wattles and numerous introduced trees and shrubs.  

Symptoms and signs of disease:

Early symptoms of this native soil borne fungus can often be difficult to detect but may include the death of branches, vertical splits on trunks, yellowing of foliage, poor vigour and the darkening and rotting of the larger roots.

Other pathogens and environmental disorders can produce similar symptoms, so it is wise to check that Armillaria infection is present by examining a tree showing advanced disease symptoms. 

Spread and infection of disease:

The fungus produces fruiting bodies (mushrooms) that are usually found at the base of affected tree trunks and stumps.  The mushrooms can be quite large, with caps between 4 and 10 cm in diameter on stalks up to 25 cm long. Their colour can vary from yellow-brown, olive-brown to golden.

Unlike some other root rot fungi, Armillaria does not infest soil. It spreads through root to root contact with infected trees, especially old decayed stumps and roots. Its spread within the roots can be up to 1 - 3 metres per year. Rhizomorphs enable the pathogen to move through the soil between trees to attack other healthy tree roots.

Drought and flooding is often associated with severe symptoms however it is fair to say that any factor that stresses trees can result in a weakened defence system and an increased likelihood of the disease developing.


At present there is no simple method for controlling Armillaria so combinations of treatments are often required. Once a tree is infected and showing symptoms in a home garden or park, there is little that can be done to save that tree.

Control can include the complete removal of the infected tree, including the tree stump and roots where possible, and delaying the planting of new trees for as long as possible. Hygiene is also very important in minimising the spread of this fungus. A combination of sanitation measures, good horticultural management can be expected to retard the activity of Armillaria.

All of the above factors need to form part of an integrated program of management for this disease. 

If you require any further information please call Naturally Trees on 9970 6332 or 0417 250 420.





Armillaria growing from dead trunk

Armillaria fungi growing at base of dead stump.