Abstract: In order to explore the dynamic relations between wheat powdery epidemic and meteorological conditions, the hourly canopy air temperature and humidity in a representative winter wheat field were measured by a field monitoring system in the wheat powdery mildew season in 2010-2012. Meanwhile, the daily wheat powdery mildew density was also investigated in the same field. By using these measured data and the standard weather station data, the correlations of the wheat powdery mildew epidemic speed with the canopy’s and ambient air temperature and humidity and their diurnal variations up to five days ahead of the powdery mildew epidemic were analyzed. The conception of ‘daily accumulated critical high air temperature hours’ was proposed to present the favorability of weather conditions to powdery mildew epidemic speed, and a set of meteorological grade indices was developed to classify the wheat powdery mildew epidemic speed. The powdery mildew epidemic forecast model based on the relationship analysis of air temperature and humidity was established, with the validation accuracy of 88%. The validation accuracy of the indices in 2009 and 2010 was 67% and 84%, respectively, and the forecasting accuracy in 2012 was 87%.  It was suggested that the established meteorological grade indices and forecast model were  applicable to the monitoring, forecasting, and assessment of winter wheat powdery mildew epidemic. This study could provide references to the plant pathology research and crop epidemics forecast.

Key words: Pinus koraiensis, climate change., tree ring, latitude