农田杂草的发生和为害,一般地说是互相关联的。但是,由于人的干预,也即通过防治,往往就把这种关联改变了,因此,发生情况并不一定就等于为害情况。由于我省过去提出的农田草害调查方法和分级标准中没有明确区分这两个不同的概念,因而在草害调查中,常常把杂草的发生情况和为害损失混为一淡。例如我们在调查了某地麦田猪殃殃的发生密度后,统计结果便得出猪殃殃“轻度发生”、“中等为害”、“严重为 The occurrence and damage of farmland weeds are generally related to each other. However, this kind of association has often been changed by human intervention, that is, through prevention and control. Therefore, the occurrence does not necessarily mean that the situation is harmful. Since the two different concepts were not clearly distinguished in the methods and grading standards of farmland weeds survey in the past in our province, the occurrence of weeds and the loss of damage were often confused in the investigation of grassland damage. For example, after we surveyed the occurrence density of cleavers in the wheat field in a certain area, the statistical results showed that the cleavers were mildly “moderate” and "severely