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The objective of the present study was to develop a computer software for simulating the temporal development of plant disease epidemics using Richards,logistic,Gompertz,monomolecular,and exponential functions,respectively,and for predicting disease with a fitted model.The software was programmed using Visual Basic(VB6.0)and packaged with the Wise Installation System.The Fibonacci(0.618)section strategy was used to find out the most appropriate value for the shape parameter(m)in Richards function simulation through looping procedures.The software program was repeatedly tested,debugged and edited until it was run through favorably and produced ideal outputs.It was named Epitimulator based on the phrase epidemic time simulator and has been registered by the National Copyright Department of China (Reg.no.2007SR18489).It can be installed and run on personal computers with all versions of Windows operational systems.Data of disease index and survey time are keyed in or imported from Access files.The output of fitted models and related data of parameters can be pasted into Microsoft Excel worksheet or into Word document for editing as required and the simulated disease progress curves can be stored in separate graphic files.After being finally tested and completed,Epitimulator(R)was applied to simulate the epidemic progress of corn northern leaf blight(Exserohilum turcicum)with recorded data from field surveys of corn crops and the fitted models were output.Comparison of the simulation results showed that the disease progress was always best described by Richards function,which resulted in the most accurate simulation model.Result also showed that forecast of northern leaf blight development was highly accurate by using the computed progress model from Richards function.