Treatment of root and butt rot in conifers


Heterobasidion annosum on Sitka spruce

The aims of this project are to optimise ways of controlling the pathogen, Heterobasidion annosum, and minimise the use of chemical pesticides wherever possible. Heterobasidion annosum (formerly called Fomes annosus) is a pathogenic fungus which kills the roots and rots the heartwood of most commercially grown conifer species. The pathogen gains entry to a crop, predominantly conifer species, when spores land on freshly created stumps. It then grows down into the root system and transfers across into the roots of adjacent trees, or a newly re-planted crop.

Research Objectives

  • Investigate whether treatments can be targeted to areas where the risks from the disease are highest
  • Investigate biological control methods on pine and spruce
  • Retain relevant EU and UK permits to continue use of two stump treatment agents
  • Examine whether chemical thinning of larch and pine affects vulnerability to Heterobasidion root and butt rot.

Results so far

Disease risk assessment:

Pine, Douglas fir and larch stumps should always be treated using a chemical or, in the case of pine chemical or biological control agent. We now know that the risk of serious disease in spruce species varies with soil type and climate. Our Disease Risk Assessment System shows that the greatest threat from this fungus comes on sites with well-drained soils and relatively mild climates, whilst the risks are lowest on upland sites dominated by wet peats

Biological control

Forest Research manufactures a biological control agent, PG Suspension, against Heterobasidion annosum. It contains spores of another fungus, Phlebiopsis gigantea, and is very successful in controlling the pathogen in the predominantly pine forests of East Anglia. It is available to anyone harvesting pine, and is a very viable alternative to the chemical treatment, urea.

PG Suspension is currently only licensed for use on pine species, but experiments are underway to see if it, and a similar Scandinavian product, Rotstop, are effective on spruce species as well. Preliminary results show that spore concentrations in the product would have to be greatly increased to make it effective on other species.

Pesticide legislation

All plant protection products are periodically reviewed across the European Union. The Forestry Commission is the permit holder for the biological agent, PG Suspension and the chemical agent, urea. Both products are under review at the moment and the Forestry Commission has submitted information on both treatment agents for review by the EU and the UK pesticides authority – Chemicals Regulation Directorate.

Heterobasidion annosum and chemical thinning

Experiments are currently underway to see if novel chemical thinning methods could be used to defoliate larch trees to try to slow or even prevent the spread of the new pathogen, Phytophthora ramorum. Chemical thinning can, however, sometimes increase infection of trees by H. annosum, and this is currently being monitored.


Disease risk assessment models are constantly being refined as further data are collected. An update will be available when the new edition of ‘Reducing Pesticide Use in Forestry’ is released.

Experimentation looking at biological control on spruce is ongoing and reviewed a regular intervals

Pesticides re-registration requirements are amended regularly and we aim to submit information to the relevant bodies if and when required.

Research into novel chemical thinning methods and impacts on Heterobasidion annosum began in 2014 and are due to conclude in late 2016.

Related services

Risk based stump treatment

PG Suspension - a prophylactic biological control product is manufactured and marketed by the Forestry Commission for use on pine species to protect surrounding and following crops against infection.

Related resources (Recent publications)

Willoughby et al., (2004). Reducing pesticide use in forestry. Forestry Commission

a pdf of a presentation on site risk assessment


Kath Tubby

Dr Steven Hendry

Funders and Partners

Research on stump treatment and associated pesticide registration requirements are funded by the Forestry Commission’s Corporate and Forestry Services, Forestry Commission Scotland and Forest Enterprise Scotland

Forestry Commission policy
Both the research and the associated ongoing tasks relating to pesticide registration are crucial to the sustainability of much of the UK’s conifer forests and protection of the wider forest ecosystems. Our aim to increase the availability and uptake of PG Suspension also very much supports the FC’s drive to adopt an Integrated Pest Management approach wherever possible, and reduce the reliance on conventional pesticides.