Late Blight Forecasting in Norway 1957–1980

A regular late-blight warning service was established in Norway in 1957, run by the Plant Protection Service. The service was revised in 1965 and from that year the warnings were distributed by the Norwegian Institute of Meteorology. The criteria for warnings are described. A regression analysis of the relationship between warnings and intensity of late-blight epidemics in 1957–1980 showed no significant differences between locations, but significant differences in the relationship between years and periods. The weather in the years 1973 to 1978 caused unfavourable conditions for late blight in all parts of the country. In 1979 and 1980 the weather changed and favourable climate to late blight occurred in most regions of the country, but the progress of epidemics in 1979 was slower than expected due to reduced inoculum potential. In 1980 a more normal progress of epidemics was observed, which indicated a reestablishment of the inoculum potential in the autumn of 1979.