Conifer butt rot (Heterobasidion annosum)

Common host(s)                    Particularly significant in conifer plantations but can also attack deciduous trees.

Colonisation strategy            Can penetrate thin skin on root tips. Spores germinate on sap-leaking surface of cut stumps. Problem in thinned or partially felled forest stands more so than ornamental plantings. Root contact or root grafts can cause cross infection.

Symptoms                              Perennial fruiting bodies, persistent, brown, reddish-brown or grey-brown with a white margin and curved edges. White/cream undersides fade in intensity. Singly or more often in overlapping groups/colonies at the very base of the trunk at ground level.

Type of rot                             White soft rot of heartwood.

Part(s) of tree affected          Root rot, but often extends up the stem for several metres.

Significance                            Very important disease of conifer plantations, in ornamentals, rotting heartwood makes tree prone to wind-snap in free-standing trees. Ultimately it will kill the tree but the trunk may distort and form adaptive growth if it has the protection of a forest. Forms bottle butt. Control by removing stumps or spraying with 20% urea.

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