Rice sheath blight and its causal agent Rhizoctonia solani AG-1 IA are associated with intensive and high input production systems. To our knowledge, resistant varieties have not been introduced for this disease, thus good crop management is expected to be among viable disease control methods. The aims of the present study were to determine the effect of different rates of nitrogen fertilizer, planting spaces and inoculum densities on sheath blight incidence and severity, including grain yield loss. Additionally we aimed to identify those developmental stages that are more susceptible to the disease. Field experiments were conducted over two consecutive years, in 2017 and 2018 in the Guilan province of Iran. Results indicated that higher N rates, denser planting and higher initial inoculum density resulted in greater disease development. Among five different growth stages, inoculation of plants at booting and flowering stages, resulted in maximum disease severity and grain yield loss. Taken together, reasonable use of nitrogen fertilizer, optimum planting space and reduced inoculum density obtained by spraying fungicide at the booting and flowering stages of rice are suggested as the best options to control sheath blight epidemics in rice.

中文翻译：

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不同流行病学条件下水稻纹枯病的发展与减产

水稻纹枯病及其病原体Rhizoctonia solani AG-1 IA 与集约化和高投入生产系统有关。据我们所知，尚未针对该病害引入抗性品种，因此良好的作物管理有望成为可行的病害控制方法之一。本研究的目的是确定不同氮肥用量、种植空间和接种密度对纹枯病发病率和严重程度（包括粮食产量损失）的影响。此外，我们的目标是确定那些更容易受到疾病影响的发育阶段。2017 年和 2018 年在伊朗桂兰省连续两年进行了现场试验。结果表明，较高的施氮量、较密的种植和较高的初始接种密度会导致病害的发展。在五个不同的生长阶段中，在孕穗和开花阶段接种植物导致病害严重程度和谷物产量损失最大。综上所述，合理使用氮肥，优化种植空间，降低水稻孕穗期和开花期喷施杀菌剂的接种密度，是防治水稻纹枯病流行的最佳选择。