制定大面积化学防治病虫计划时,必须大体计算支出与收益的关系。一般病虫为害轻时不需施药,只有当为害造成的经济损失可能大于施药支出时,才宜施药防治。但为害过重时才施药,施药支出虽能挽回较大的产量损失,但绝对损失量过大,这也不可取。为了寻找棉田防治地老虎施药支出与挽回损失大致相等的关系即经济阈值或经济指标,我们做了如下探讨。 When formulating a large-scale chemical pest control plan, the relationship between expenditures and benefits must be roughly calculated. Insects and diseases generally do not need pesticide light, only when the damage caused by the economic losses may be greater than the spending of drugs, it is appropriate pesticide control. However, when the pesticide was overkill, pesticide expenditures could recover the larger output loss, but the absolute loss was too large, which is not desirable. In order to find out about the cotton fields to control the spending of pesticides and restore the roughly equal loss of economic relations that the threshold or economic indicators, we made the following discussion.