Development and Implementation of a New National Warning System for Potato Late Blight in Great Britain

  • Siobhan Dancey

Student thesis: Doctoral ThesisDoctor of Philosophy


Phytophthora infestans (Mont) De Bary, the cause of potato late blight, is arguably the most important species of the genus Phytophthora in terms of economic losses and the cost of fungicides used for its control. The Smith Period is a set of temperature and humidity criteria that comprise the national warning system for late blight in Great Britain and is used by the potato industry to aid in appropriate scheduling of fungicide treatments. It was developed in the 1950’s and has not been reviewed or modified since its inception. In that time, there has been a change in British weather conditions and a change in the diversity and aggressiveness of the pathogen population. The performance of the Smith Period was examined using a back-testing analysis with a historical national-scale, longitudinal outbreak dataset and corresponding weather data. ROC analysis revealed significant regional variation in the ability of the Smith Period to forecast outbreaks. A series of controlled environment experiments were performed to refine the temperature and humidity criteria that define risk of infection, using isolates of P. infestans representative of the contemporary pathogen population in Great Britain. The results showed significant levels of infection under drier (less humid) conditions than prescribed by the Smith Period. These findings were used to develop candidate replacement models for the Smith Period. These were tested for their ability to forecast late blight outbreaks using the same back-testing analysis framework as for the Smith Period. The best prediction outcome was a model that requires two consecutive days with a minimum temperature of 10°C and at least 6 hours each day with a relative humidity ≥90%. This model was named the ‘Hutton Criteria,’ and was launched by the Agricultural and Horticultural Development Board Potatoes division as the new national warning system for late blight in GB in 2017.
Date of Award2018
Original languageEnglish
SupervisorDavid Cooke (Supervisor), Peter Skelsey (Supervisor) & Paul Birch (Supervisor)

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