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Determining Best Methods For The Clearance And Disposal Of Key Host Plants, Especially Invasive Rhododendron, For The Control Of The Quarantine Plant Pathogens Phytophthora Ramorum And Phytophthora Kernoviae - PH0603

In April 2009 Defra launched a five-year programme to protect at-risk plants and environments from the quarantine pathogens Phytophthora ramorum and P. kernoviae. Part of the programme includes research to inform and support the overall disease management activities. The research being undertaken in this project supports the policy objectives of the programme which require that by the end of Year 5 (April 2014), tools, knowledge and evidence for sound disease eradication, containment and management are fully developed for use in gardens, nurseries, natural habitats and the wider environment. Specifically this project will:
• Develop evidence-based management practices and control methods particularly applicable for use in woodlands, parks and gardens.
• Test chemical, non-chemical and cultural methods for managing the pathogens, as well as improved approaches for management of infected and uninfected waste.

In Britain it has been established that epidemics of P. ramorum and P. kernoviae are driven by infected rhododendron, usually Rhododendron ponticum, which is a major sporulating host for both pathogens. Eradication of rhododendron is the accepted control measure to prevent disease spread, but even with established clearance methods, fully effective disease control is impeded by several factors. These include the need for repeat herbicide applications to rhododendron stumps to prevent resprouting otherwise reinfection occurs; the difficulties and expense surrounding safe disposal of infected rhododendron which may involve removal off site; and the long term persistence of both pathogens on affected sites post-rhododendron clearance. This project will evaluate a range of conventional and novel methods to address these challenges. The work will be undertaken on at least two landscape sites which require clearance and the research will be closely coordinated and linked with current eradication and containment actions being undertaken by Defra/Fera on the ground.
Firstly, to improve long term clearance of infected rhododendron three management options will be evaluated. (1) Use of alternative chemical herbicides (tryclopyr, amitrole and aminopyralid) because of their potential to provide much better sprout control than the currently used chemical option. (2) As a futher option, the bioherbicide Chondrosterum purpureum will be tested for sprout control because of the addition benefits that it can offer in relation to reduced environmental impacts and rapid breakdown of stumps which may otherwise harbour Phytophthora after rhododendron clearance. (3) Another option will explore the efficacy and costs of mechanical stump treatment which can also inhibit resprouting and avoids herbicide inputs in areas under treament.
Secondly, alternative methods for disposal of infected rhododendron biomass on-site will be evaluated. In particular, the possibility for cost off-setting in the clearance process through production of biochar (charcoal) using portable reactors. Useful outputs of the process include not only the charcoal, which has a market value, but the steam generated during production can be used for soil sterilisation to eliminate any residual Phytophthora inoculum remaining in soil after clearance. As a contrast, low technology methods of accelerated decomposition of rhododendron biomass which remains on site after cutting will also be tested. The trials will make use of cheap and widely available acclerators such as urea and chicken manure. The effectiveness of the accelerated decomposition will be measured by assessing speed of volume reduction as well as the rate at which Phytophthora is eliminated from the decomposing material.
Finally, a recently discovered transitory anti-microbial treatment (patent application GB0821159.1) will be tested on cleared but but still infected sites as another approach to clearing residual Phytophthora inoculum from the soil and litter layers.
As the project is concluded, the outcomes from the three strands of experimental work will be compared and the new information drawn together to identify the Best Management Practice (BMP) for the eradication and containment of Phytophthora ramorum and P. kernoviae affected environments, where infected rhododendron forms a significant component. In addition, the analysis will also give recommendations on how the various experimental treatments can be up-scaled for use within the Fera Phytophthora Programme for sites under notice for containment or clearance.
Scientific objectives

1. Investigate the efficacy of specified chemical, biological and physical treatments for application to rhododendron stumps, with the aim of finding improved treatments which reduce or eliminate the need for repeat treatments to prevent stump re-sprouting and help reduce inoculum levels by killing the stumps and live root material used as a host by Phytophthora.

2. Determine the extent to which charcoal production offers a cost-effective and safe method for on-site disposal of infected rhododendron biomass.

3. Determine the effectiveness of compost-accelerated decomposition of cut infected rhododendron biomass as an alternative low-cost method aimed at reducing the volume of rhododendron residues on-site, whilst also enhancing levels of anti-Phytophthora microbes to reduce persistence of Phytophthora ramorum and P. kernoviae contamination.

4. Investigate the potential of transitory antimicrobial compound (patent application GB0821259.1) to destroy inoculum of P. ramorum and P. kernoviae and reduce contamination on infested sites.

5. Contrast the outcome of these trials to define and recommend the most effective strategies for management and eradication of P. ramorum and P. kernoviae on infested sites in environments where rhododendron forms a significant component.
Project Documents
• FRP - Final Report : Determining Best Methods For The Clearance And Disposal Of Key Host Plants, Especially Invasive Rhododendron, For The Control Of The Quarantine Plant Pathogens Phytophthora Ramorum And Phytophthora Kernoviae   (3232k)
Time-Scale and Cost
From: 2010

To: 2013

Cost: £251,031
Contractor / Funded Organisations
Forestry Commission Research Agency, CABI Bioscience
Plant diseases              
Plant health              
Plants and Animals