1980年,上海郊县后季稻普遍发生了穗颈稻瘟病,严重影响了粮食产量。我县后季稻有21.28万亩发生了不同程度的穗颈瘟,占种植面积的53％。平均病穗率达46.54％,病情指数为33.91,平均损失率为16.47％,是最近十六年中发病最严重的一年。现就大发生的原因分析如下。 (一)气候条件对作物不利,而有利发病:一是后季稻苗期气温低,阴雨多,日照少。据县气象部门资料,在6月21日～8月 22日,10℃以上的有效积温比1979年同期少89.7℃,雨量多229.3毫米,日照少84.2小时。以致秧苗长得慢,素质差,抗病力低,苗稻瘟和叶稻瘟比较普遍,从而增加了后期穗颈瘟菌原。二是穗期低温早,时间长。9月中、下旬,日平均气温低于20℃的始期,比1979 In 1980, the occurrence of panicle blast occurred in the latter part of the suburbs of Shanghai, which seriously affected the grain yield. There were 21.28 million mu of post-season rice in our county with varying degrees of panicle blast, accounting for 53% of the acreage. The average ear disease rate was 46.54%, the disease index was 33.91, the average loss rate was 16.47%, which was the most serious one in the recent 16 years. Now the reason for the big analysis is as follows. (A) the climatic conditions adverse to crops, and favorable incidence: First, the post-season rice seedling temperature is low, more rainy, less sunshine. According to the county meteorological department data, effective June 21 ~ August 22, the effective accumulated temperature above 10 ℃ less than 89.7 ℃ over the same period in 1979, more rainfall 229.3 mm, less sun 84.2 hours. Resulting in seedlings grow slowly, poor quality, low resistance to disease, rice blast and leaf blast is more common, thereby increasing the late panicle Magnaporthe grisea. Second, ear low temperature early, a long time. In mid-September, the average daily temperature was below the initial period of 20 ℃, more than 1979