Being used as a mathematical model of the latent period, a prognostic equation for probability of apparition, which is determined mainly by accumulated effective temperatures in the case of wheat stripe rust, is derived on the basis of experimental data.In field inoculation experiments of stripe rust on the susceptible wheat cultivar YD1817, the numbers of rusted leaves that were initiated by the infection that occurred on the i-th day and were just erupting into uredium pustules on the j-th day were observed every day. In the plots with accumulated effective temperatures as abscissa and with accumulated probability of apparition as ordinate, distribution of relevant points for the observed results from 14 experiments follows an S-shaped curve. Among the three models, namely, the Weibull function, logistic model, and Sine-square model, the logistic model seems to be the most fitted one with the determining equation: where PP_i is the accumulated probability of apparition on i-th day and TT_i is the accu Being used as a mathematical model of the latent period, a prognostic equation for probability of apparition, which is determined mainly by accumulated effective temperatures in the case of wheat stripe rust, is derived on the basis of experimental data. In field inoculation experiments of stripe rust on the susceptible wheat cultivar YD1817, the numbers of rusted leaves that were initiated by the infection that occurred on the i-th day and were just erupting into uredium pustules on the j-th day were observed every day. effective temperatures as abscissa and with accumulated probability of apparition as ordinate, distribution of relevant points for the observed results from 14 experiments follows an S-shaped curve. Among the three models, namely, the Weibull function, logistic model, and Sine-square model , the logistic model seems to be the most fitted one with the determining equation: where PP_i is the accumulated probability of apparition on i-th day an d TT_i is the accu