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Underpinning regulatory decisions on fungicide resistance risk assessment - PS2712

Description
The threat posed by resistance to the sustainability of agricultural systems, together with the uncertainties of resistance risk assessment, has led the ACP to recommend that PSD takes a more precautionary approach to resistance management. The challenge is to make robust regulatory decisions whilst avoiding undue restrictions on use and unacceptable additional development costs for applicants. This project aims to quantify the net benefit of different resistance management strategies, so that options can be compared and the reasons for regulatory decisions can be made explicit.

Objectives - Reduce uncertainty in resistance risk assessment:
1. Quantify the effect of epidemiological, genetic and agronomic factors on the evolution of fungicide resistance.
2. Transfer resulting knowledge on the factors determining the risk of fungicide resistance as a basis for provision of guidance on, and consideration of, resistance risk assessments for new fungicides.
Objectives - Target resistance management strategies:
3. Develop models of the evolution, invasion and persistence of fungicide resistant strains.
4. Apply the models to quantify the effect on invasion and persistence of resistant strains of (i) dose, (ii) number of treatments, (iii) mode of action mixtures, (iv) alternation and (v) spatial and temporal refugia.
5. Transfer resulting knowledge on the factors determining the effectiveness of different resistance management strategies and develop a rational basis for improved fungicide resistance management.
6. Assess the extent to which the techniques developed might have generic value for application across insecticide and herbicide resistance management.

Methods - Resistance risk assessment:
Hypotheses will be defined relating resistance risk to evolutionary forces, and then tested for predictive value against a large historical data set. The data will be used to quantify risk (measured as time from approval to first detection of resistance, rate of efficacy loss, and time to end of useful life) and the factors hypothesised to be determinants of selection (principally, pathogen reproductive system, genetics of resistance, pathogen life-cycle parameters, fungicide activity and fungicide usage). We will assess whether the revised method significantly improves the predictive value of the risk assessment, compared against the current scheme.
Methods - Resistance management strategies:
We will study specifically how the resistance management options in Efficacy Guideline 606 apply to systems with different characteristics, using some of the relevant understanding developed in relation to antibiotic
resistance to improve on current theory in relation to plant pathogens. Selection for resistance occurs through differential efficacy against strains which vary in sensitivity to the active substance. Efficacy (the desirable effect of use) and selection (the undesirable side effect of use) are closely linked. Hence, it is important to be able to quantify the extent to which efficacy has an economic benefit, as treatments which give control (and its associated selection) but little benefit, might be a logical target for regulatory constraint.
The main effect of foliar applied fungicides is to protect green canopy area. The economic benefit is determined by the amount of that protection which has its effect during the yield-forming period. Hence, the effect of the fungicide and the build up of resistance will be quantified here by the green leaf area gain (LAG) during the yield forming period.
The model will be formulated as two sets of non-linear differential equations for the pathogen strains; the first set modelling the dynamics of the pathogen strains during the growing season and the impact on green canopy area, and the second describing pathogen dynamics between growing seasons. The effectiveness of each potential resistance management strategy will be quantified by the difference in LAG with and without applying the strategy. This summary statistic combines the effects of increased green leaf area due to the use of fungicide (positive effects), the increase in the fraction of the resistant strain in the pathogen population (negative effects), and any effect of regulation constraining use (initially negative, then positive in good strategies due to retention of efficacy).

Deliverables:
1. Predictive methods to underpin guidance to applicants on risk analysis and to aid assessment by PSD.
2. Identification of key data requirements for assessment of resistance risk during the registration process.
3. Workable methods to evaluate the contribution of each component of resistance management strategies to the prevention or delay of fungicide resistance, according to the characteristics of the pathogen:fungicide combination under consideration.
4. Peer review of these deliverables by publication in internationally refereed journals.
Objective
Reduce uncertainty in resistance risk assessment (Work Package 1)
1. Combine understanding of resistance mechanisms with a compilation of existing data sets from contrasting pathogen/mode of action combinations, to quantify the effect of epidemiological, genetic and agronomic factors on the evolution of fungicide resistance.
2. Transfer resulting knowledge on the factors determining the risk of fungicide resistance in a convenient form for PSD technical specialists as a basis for provision of guidance on, and consideration of, resistance risk assessments for new fungicides.
Target resistance management strategies (Work Package 2)
3. Develop models of the evolution, invasion and persistence of fungicide resistant strains.
4. Apply the models, using a compilation of existing data sets, to quantify the effect on invasion and persistence of resistant strains of (i) dose, (ii) number of treatments, (iii) mode of action mixtures, (iv) alternation and (v) spatial and temporal refugia (as affected by spray timing, mobility or untreated areas).
5. Transfer resulting knowledge on the factors determining the effectiveness of different resistance management strategies in a convenient form for PSD technical specialists and develop a rational basis for improved fungicide resistance management.
6. Assess the extent to which the techniques developed might have generic value for application across insecticide and herbicide resistance management.

Objectives 1 and 2 will be addressed in Work Package 1 which will cover a wide range of foliar, stem-base, root and seed-borne pathogens. Objectives 3 to 6 will be addressed in Work Package 2 which will focus on important foliar pathogens, where resistance issues have proved intransigent.

Project Documents
• EVID4 - Final project report : PS2712 final report   (670k)
Time-Scale and Cost
From: 2008

To: 2012

Cost: £574,835
Contractor / Funded Organisations
Rothamsted Research (BBSRC), ADAS UK Ltd.
Keywords
Arable Farming              
Cereal Production              
Control              
Crop Diseases              
Crops              
Disease Control              
Disease Prevention              
Environment and Health              
Epidemiology              
Farming              
Fungicide use              
Pesticide use              
Plant diseases              
Resistance              
Risk assessment and management              
Fields of Study
Pesticide Safety