1.玉米主要病害1.1玉米大斑病:主要危害叶片,严重时波及叶鞘和包叶。田间发病始于下部叶片,逐渐向上发展。发病初期为水渍状青灰色小点,后沿叶脉向两边发展,形成中央黄褐色边缘深褐色的梭形或纺锤形的大斑。湿度大时病斑愈合成大片,斑上产生黑灰色霉状物,致病部纵裂或枯黄萎蔫;果穗、包叶染病,病斑不规则。防治方法:1选用抗病品种是防治大斑病的根本途径。2农业措施。轮作倒茬深翻可减少菌量;彻底清除田间病残体,可减少初 1. The main diseases of corn 1.1 Big spotted corn disease: the main hazard leaves, severe cases involving the sheath and leaf sheath. Field incidence began in the lower leaves, and gradually upward. Early onset of water-like green-gray dots, along the veins to both sides of the development of the formation of central brown edge dark brown fusiform or spindle-shaped large spot. When the humidity is large, the lesion is healed into a large piece, the dark gray-gray mildew is produced on the spot, the longitudinal part of the pathological part is withered or wilted; the ear, the leaf and the leaf are irregular, and the spot is irregular. Control methods: 1 Selection of resistant varieties is the fundamental way to prevent big leaf spot. 2 Agricultural measures. Rotation of stubble deep turn can reduce the amount of bacteria; complete removal of disease in the field, can reduce the beginning