The epidemiology of potato blight in the East Midlands 1923–74

SUMMARY Examination of the East Midlands records of potato blight epidemics and the meteorological data on critical 90 % relative humidity infection periods for the years 1923–74 indicates the importance of the amount of inoculum carried over from one season to the next in influencing the rapidity of progress of the disease and the date of destruction of the haulm. The success of forecasting outbreaks based on 90% r.h. periods is reviewed. The importance of taking into account both amount of inoculum and weather conditions in devising a disease control programme is discussed. It is concluded that the succession of seasons since 1968 without a major potato blight epidemic was due mainly to a combination of low carry-over of infection and sub-optimal weather conditions for the development of the disease and that the current control measures have not yet been subjected to a severe test.