Mechanistic computer simulators of plant disease have been part of plant disease epidemiology since the mid 1960s. Several simulators for specific diseases were constructed between the late 1960s and into the 1980s. However, for most simulators after the initial announcements, there have been almost no reports in which the simulators have been used - either in a practical or theoretical manner. An exception is the Cornell late blight simulator. This model has been used extensively to address both theoretical and practical questions. It has been improved and updated at irregular intervals following its initial publication. Most recently it was updated to include the characteristics of strains recently introduced into the USA from Mexico. Its potential to be the core of a Decision Support System for real-time disease predictions (in combination with real-time weather forecasts) is currently being investigated.