人、畜有时患病,尽人皆知,没人为此大惊小怪。可是说到农作物有时也会生病,有人就会感到奇怪了。其实农作物生病的事例到处都有。就说小麦吧,在生育后期麦叶和茎秆上长的黄疸,麦穗上的黑霉,叶片上的白粉,都是一种病状。玉米植株上出现的“大灰包”,马铃薯叶片上出现的轮状褐斑,薯块的腐烂亦是一种病状。这些都是农作物生病后的外部症状。那么,农作物为什么会生病呢?概括地说有两个原因。其一,当农作物受到不良的外界环境条件的影响,正常的生理活动就会遭到破坏。像干热风危害造成的小麦青枯;冻害造成的死苗;农作物缺铁后出现的白化,都没有传染性,叫做非侵染性病害。其二,像小麦的黄疸、玉米的“灰包”,都是由病原菌传染发生 People, livestock sometimes sick, well-known, no one fuss about this. But when it comes to crops that sometimes get sick, some people find it strange. In fact, there are cases of sick crops everywhere. Say it wheat, jaundice in the late growth of wheat leaves and stalks, black mold on the ears, leaf white powder, are a symptom. The emergence of “big gray bag” on corn plants, roundish brown spots on potato leaves, rotting potato tubers is also a symptom. These are external symptoms after the crop has become ill. So why are crops sick? Generally speaking, there are two reasons. First, when crops are exposed to poor external environmental conditions, normal physical activity can be disrupted. Like the dry hot wind damage caused by wheat sclerosis; frost damage caused by dead seedlings; iron deficiency appeared after crop albinism, are not contagious, called non-invasive diseases. Second, like jaundice in wheat, corn “gray package”, are transmitted by pathogens