Abstract: The scab is a usual disease of wheat.The temperature and humidity have important effects on the occurrence of wheat scab.So choosing proper temperature and humidity indices is the key for acquiring higher forecasting exactness rate.The change of early heading of wheat was analyzed by using the data of meteorological and wheat stages and wheat scab data.As the beginning of the wheat early heading stage became earlier,the forecast accurate rate declined by the old indexs,which were the mean temperature above 15℃ and the mean relative humidity by 85% in continual three days from the second ten days of April to the second ten days of May.Comparison and practical forecast tests showed that the new index was the mean temperature higher above 13℃ and the mean relative humidity by 83% in continual three days from the early heading stage of wheat to the second ten days of May.The practical application showed that the forecast accurate rate by the new index was improved from 60.0% to 83.3 %.

Key words: Wheat scab, Wheat scab, Forecast, Temperature and humidity index