水稻白叶枯病是浙江稻区常发流行性病害，调查研究其为害与损失，科学制订防治指标，对于有效预测和综合防控病害，确保水稻丰产和农民增收具有重要意义。通过对浙江桐庐、余杭等地几年来水稻白叶枯病发生为害损失调查测定，探明了病害发生为害与损失的关系，分别建立了水稻分蘖、圆秆拔节和孕穗破口期株、叶发病率与产量损失率关系的6个模型，考查了侵染发病对主要经济性状的影响，受害稻株株高下降、实粒数减少、空秕率增加是导致减产的主要原因。调查分析了田间用药和防治成本，测定了经济允许水平，首次提出了该病防治指标为水稻株发病率5%、叶发病率3%。该指标经浙江桐庐、温岭、温州等地大田验证与示范应用，与实际发生为害情况相符，药治面积压缩1/3，省药、节本、增效，取得了显著的经济、社会和生态效益。

Rice bacterial leaf blight （BLB） is one of the most common epidemic rice disease in Zhejiang Province. Investigating the yield losses and scientifically making control threshold are important for effective forecast and integrated control of the disease, and also have great significance to ensure the rice harvest and farmers’ higher income. In this study, through investigation of the occurrence, damage and yield losses caused by BLB in Tonglu and Yuhang in these years, the authors built six yield loss models based on independent variables of rice plants morbidity or rice leaves morbidity respectively, in tillering, jointing and booting stage, to show the relationship between BLB occurrence and yield losses. By the investigation on the main economic influence from BLB infection, the authors found that infected plants had lower height, fewer filled grains and higher blighted rate, which mainly caused the yield loss. On the basis of tested field pesticide costs and economic threshold, the authors first proposed the threshold value of control as 5% rice plants morbidity and 3% rice leaves morbidity. After field verification and application in Tonglu, Whenling and Wenzhou, et al, the control threshold was proved to be consistent with the actual situation, which reduced pesticides using area by one third, decreased pesticide consumption, controlled the costs, improved efficiency, and eventually acquired rather remarkable economic, social and ecological benefits.