Estimating the global severity of potato late blight with GIS-linked disease forecast models

Global severity of potato late blight was estimated by linking two disease forecast models, Blitecast and Simcast, to a climate data base in a geograp hic information system (GIS). The disease forecast models indirectly estima te late blight severity by determining how many sprays are needed during a growing season as a function of the weather. Global zonation of estimated l ate blight severity was similar for both forecast models, but Blitecast gen erally predicted a lower number of sprays. With both forecast models, there were strong differences between potato production zones. Zones of high lat e blight severity include the tropical highlands, western Europe, the east coast of Canada and northern USA, south-eastern Brazil and central-southern China. Major production zones with a low late blight severity include the western plains in India, where irrigated potato is produced in the cool dry season, north-central China, and the north-western USA. Using a global GIS data base of potato production, the average number of sprays was calculate d by country. These averages were compared with estimates of current fungic ide use. The results using Blitecast and Simcast were correlated but only B litecast estimates correlated with observed data for developed countries. T he estimated number of sprays, whether from Blitecast or Simcast, did not c orrelate with the observed number of sprays in developing countries, and in a number of developing countries the predicted optimal number of sprays wa s much higher than the actual number observed. In these countries, increase d access to host resistance and fungicides could have a strong economic imp act.