Pesticide resistance: assessment of risk and the development and implementation of effective management strategies

Insecticides, fungicides and herbicides are critical to successful crop production, but the development of pesticide resistance is a continual threat, especially to many of today's selective toxophores with specific binding sites. In order to manage resistance effectively, an assessment of genetic, ecological and operational risk factors is required, which must then be translated into meaningful local strategies that can be implemented through appropriate labelling of products and education of end users. Assessing resistance risk is a fundamental part of the development process for new molecules and is increasingly becoming a requirement of registration alongside toxicological and environmental risk data. Laboratory studies, including elucidation of target sites and metabolic degradation pathways, mutagenesis, computer models and cross-resistance tests, and field studies, including establishment of baseline sensitivities and evaluation of anti-resistance strategies, all play a part in such assessment. The challenge is then to devise management strategies which are relevant to local practice and actually reduce selection pressure to a point where product life is preserved. A preventative strategy should be in place at time of launch and for most pesticides, regional co-operation between all interested parties, of the kind advocated by the Resistance Action Committees of GCPF (Global Crop Protection Federation), increases the chance of success. Implementation of strategies via a universal product labelling system, already practised in some herbicide markets, is seen as a key way to improve product usage patterns. Monitoring resistance levels in field populations after product launch enables any fine tuning of tactics over time, for example in response to new technologies such as transgenic varieties being introduced. The limited successes in resistance management in Australia, Zimbabwe, Europe and USA are not so easily achieved in small-holder farming in developing countries, as exemplified by continuing problems in parts of India and China. Emphasis must be given to the education of growers and dealers in IRM and IPM, and improved extension services, in order to bring about a more sustainable approach to crop protection.