Conifer root and butt rot (Heterobasidion annosum)
Present in UK
Not notifiable - see 'Report a Sighting' below
Scientific name of causal agent - Heterobasidion annosum
Conifer root and butt rot is a disease of many species of conifer trees, and is one of the most serious diseases of commercial conifer forestry.
It is caused by the basidiomycete fungus Heterobasidion annosum (H. annosum), which¬†attacks the roots, butts and stems (trunks). The fungus previously had the scientific name¬†Fomes annosus.
There are high levels of H. annosum infecton in mainland Europe, but the problem is less severe in the United Kingdom. It affects up to 25 per cent of Norway spruce (Picea abies) in Scandinavia, and causes tree decay that results in losses of hundreds of millions of euros every year.
The disease is less prevalent in the UK because our conifer stands have been intensively managed for only a relatively short period (fewer than 200 years) compared with those in continental Europe. H. annosum spores are therefore relatively infrequent, so infection levels remain lower than in Europe. However, there is a risk that spore levels might increase over time.
Identification and symptoms
The fungus colonises tree stumps from recent thinning or clear-cutting operations.
It grows down through the root stumps.
If the roots of infected stumps are in contact with the roots of living trees, it can infect the living trees.
It causes decay in the lower stems of many coniferous species, hence the name¬†conifer root and butt rot.
It kills pines (trees in the Pinus genus) on vulnerable sites.
Report a sighting
Conifer root and butt rot is most likely to occur on commercial forestry sites, whose managers are trained to recognise and manage it. We therefore do not require reports of suspected sightings from members of the public.
Management and control
The risk of infection depends upon the¬†soil type, climate and crop management.
Prophylactic stump treatment prevents infection of standing crops.
Fresh stump surfaces are sprayed with chemical or biological agents.
Stump treatment prevents H. annosum infection, and it accounts for 90 per cent of all plant protection product use in British forestry. Forest Research has been conducting field trials of two non-chemical treatments, PG Suspension, which is currently only registered for use on pine species, and Rotstop, which is registered in Scandinavia for use on Norway spruce and pine (Pinus) species.