Abstract: This work was carried out during 1987-1988.Field experimemts were distributed at three locations in Henan province.Four cultivars were used as experimental materials and different severity of disease was made by different intensity of field inoculation.The result showed that when the disease index increased by 1%,the yield loss increased by 0.5%, the percentage of the diseased ear increased by 1.3% and the percentage of diseased grain increased by 0.5%.The economic threshold of controlling the disease was based upon the yield level of wheat crop.If the yield level ranged at 4.5,5.25 and 6.0 tons per hectare,the disease indices of economic thresholds of controlling were calculated as 2.3%-2.7%,1.9%-2.3% and 1.6%-2.6% respectively.The extension of the usage of these economic thresholds was also dicreased.

Key words: Wheat scab, Yield loss, Economic threshold