Clearance and disposal strategies for Phytophthora-infected rhododendron

Summary

Phytophthora ramorum and P. kernoviae are fungus-like plant pathogens that can cause severe damage and mortality of trees in Britain. One of the main sporulating hosts of both pathogens, on which they can grow and spread into new areas, is Rhododendron ponticum, and this is commonly found growing as a woody weed in British forests and woodlands. Eradication and control of rhododendron is currently one of the most effective control measures to reduce the spread of the pathogen and disease into new areas.

However, eradication of rhododendron poses a number of problems:

• Mechanical clearance must be followed by repeated herbicide applications for at least two years to prevent resprouting and recolonisation. This is expensive and has a high environmental impact.
• Rhododendron plants can be large and dense, making clearance very difficult and generating a lot of material for disposal.
• The woody waste material must be disposed of in compliance with strict regulations to ensure other locations are not infected.
• Both pathogens can persist in the soil and leaf litter for 3-5 years after clearance. This can apply not only to the leaf litter generated from infected rhododendron, but also the litter from larch (Larix) and bilberry (Vaccinium) which P. ramorum also infects.

Research objectives

This collaborative project was developed to identify new or improved management strategies for the eradication and safe disposal of Phytophthora infected rhododendron, and methods which reduce pathogen persistence on infected sites.

The project had two strands:

• Improving strategies for long-term eradication of rhododendron
  Testing and evaluation of three management options: (1) use of alternative chemical herbicides, (2) use of the bioherbicide Chondrostereum purpureum, and (3) mechanical stump treatments.
• Methods for disposal of infected material and site remediation
  Evaluation of: (1) disposal through production of biochar, (2) use of the steam generated for on-site soil sterilisation, (3) accelerated decomposition of infected biomass using urea and chicken manure and (4) deployment of heat-treated woodshavings which have been shown to have anti-microbial activity.

The project draws together experience from field experiments to identify the best management practice for the eradication, containment and remediation of Phytophthora-affected environments, where infected rhododendron forms a significant component.

Funders and Partners

The collaborative project is funded by Defra (project PH0603) and is implemented by three partners: Forest Research, CABI E-UK and the University of Surrey.

Forestry Commission policy

The research project will directly support the Defra Phytophthora Disease Management Programme for P. ramorum and P. kernoviae in England and Wales. The work addresses a key policy objective within the programme to evaluate disease management and control methods. The outputs of the project will support the Disease Management Workstream of the Programme, which has the aim of eradicating infected sporulating host plants, principally Rhododendron ponticum, an invasive, non-native plant.

Status

The project ran 2010-2013.

Contact

For further information contact:

Dr. Joan Webber