历年事实证明,晚季作物病虫害往往比早季严重。因为一种病虫要致成灾害,必须经过由少到多的繁殖累积过程。与早季相比,晚季病虫不仅基数高,而且繁殖快。因此,晚季病虫繁殖代数多,虫源、菌源积累数量大。这是晚季病虫害为什么往往重于早季的主要原因。例如三化螟,在我省一年有四代,有的年分出现五代。早季基本完成第二代;晚季是从虫口 Historical evidence shows that late season crop pests and diseases are often more serious than in the early part of the year. Because a pest and disease can cause a disaster, it is necessary to go through the breeding and accumulation process from as little as possible. Compared with the early season, late-season pests not only high base, but also reproduce fast. Therefore, the late generation of pests multiply generations of algae, insect sources, the accumulation of large number of bacteria. This is the main reason why late season pests and diseases are often more important than the early season. For example, rice stem borer, four generations a year in our province, and some years appeared five generations. Basically completed the second generation of the early season; late season is from the mouth