Monitoring Fungicide Resistance: Purposes, Procedures and Progress

The effectiveness of monitoring as an early warning system is discussed in relation to both discrete and continuous modes of resistance buildup. Monitoring can also be done to check that avoidance strategies or limitations are working, to investigate cases of suspected loss of performance, to track the spread or intensification of resistance with time, to guide fungicide selection at local level, to gain understanding of the behaviour of resistant forms in field populations, and to validate predictive models. The choice of methods of sampling and bioassay is considerable, and will depend upon the pathogen, the host, the degree of estimated risk, availability of labour and other factors. Agreement between methods is often good, but some anomalies and pitfalls are described as is the great advantage of having ‘base-line data’ and a collection of early isolates. The need to monitor practical performance as well as isolate responses is also emphasised. DNA probes or other biochemical detectors of fungicide resistance are not yet available, but would be valuable especially for epidemiological studies of resistance. The value of some reported monitoring exercises is appraised, and the requirement is stressed for more sustained studies, for full, prompt publication of results, and for increased public-sector and industry interaction in planning and interpretation.