IThe Lateblight application is designed to allows students to manipulate the variables that affect the development of late blight, a disease of potatoes and tomatoes caused by the fungus Phytophthora infestans, and to adjust the economic parameters that determine the cost-effectiveness of the disease management procedures. Different potato cultivars can be simulated by altering the level of resistance to the fungus, the time of initiation of tuber production, and the yield potential of the crop in the absence of disease.
A simulation is initiated by selecting a weather data file. The weather data determine the environmental conditions under which the simulation will execute—cool and wet, hot and dry, or moderate temperature and rainfall. Users then set the characteristics of the potato cultivar that they want to simulate—a low, moderate, or high level of resistance to P. infestans, tuber initiation occurring early, mid, or late season, and themaximum yield potential. As with real epidemics, the initial inoculum in Lateblight can be introduced as sporangia, lesions, or both. Finally, the production costs and the market price for the harvested potatoes can be set. All of these start-up values can be saved in a disk file to facilitate repeated simulations using the same initial values for most of the parameters.
The Simulation window for Lateblight (shown above) displays the results of the simulation. During the season the simulation can be stopped so that the user can consult the weather forecast and the Blitecast spray advisory in order to decide if it would be advisable to apply a spray of either a protectant or a systemic fungicide. The costs of using the Blitecast spray advisory and of applying a spray must be balanced against the potential of greater potato yield. An economic summary can be displayed at the end of the season.
Several output variables can be graphed on the screen—the fungicide residues, rainfall, daily mean temperature, hours of relative humidity above 90%, leaf area index, latent lesions, sporangia production, percent foliage blight, and area under the disease progress curve.
(This version was adapted from the simulation originally written by J. A. Bruhn et al. (1980) and modified by people in the research program of W. E. Fry, Dept. of Plant Pathology, Cornell University.)