This project aims to exploit developments in molecular diagnostics (quantitative real time PCR) to allow optimisation of integrated control measures (including minimal irrigation and non-water based measures), suited to specific production conditions, to ensure maximum suppression of common scab-forming Streptomyces spp. Novel molecular diagnostic technology will be applied for the first time to further understanding of the population dynamics of competing populations of pathogenic and non-pathogenic Streptomyces spp. on and around developing potato tubers and in response to varying control measures. Used concurrently with conventional microbiological techniques, molecular assays will enable quantitative and accurate study of the effect of external stimuli (such as irrigation treatments or amendments affecting microbiological, pH or nutritional balance) on suppression of pathogenic populations and their interaction with total streptomycete populations. It is intended that this approach will allow definition of precise water management requirements and/or integration of alternative factors to maximise suppression of the pathogenic Streptomyces strains for a variety of production conditions (soil types, cultivars etc). Common scab can be largely eliminated if irrigation is timed correctly and achieves uniform wetting of the ridge or bed around the initiating potato tubers. However, there are some soils where it is difficult to achieve blemish-free tubers even with very frequent irrigation. Identification of the strains of Streptomyces in such soils and their dynamics during the scab control phase is important in improving irrigation strategy. Conversely, there exist “suppressive” soils that seem to largely avoid common scab even in the absence of irrigation. Identifying the strains and pathogenicity of Streptomyces strains in such soils in relation to water and nutrient status, pH and the relative populations of antagonistic micro-organisms would help understand how common scab development varies in different soils. Different soils appear to have different optimal moisture contents for common scab control; establishing these optima for a wider range of soils will improve the efficiency of irrigation. Understanding the dynamics of Streptomyces populations during wetting and drying cycles will help determine these optima more rapidly. A quantifiable estimate of the Streptomyces population in the soil would permit growers to establish whether irrigation is likely to be fully effective before committing the resources. This will improve the efficiency of water application by the UK industry.