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秋季大白菜最易发生霜霉病,严重的年份可减产50—60％。大白菜得病后,叶背面出现霉状物,而叶正面无明显症状。整林被害后,叶背出现白色霜霉,叶正面出现淡绿色病斑。病斑扩大时,受叶脉限制而形成多角形或不规则形、大白菜进入包心期后,若环境条件适合,病情发展很快,病斑迅速增加,使叶片枯死。此病一年有两次高峰期,第一次在8月下旬至9月上旬,第二次在9月下旬到10月初应抓早进行。常用的农药有40％乙磷铝可湿性粉剂200—300倍液,或者80％代森锌600倍液。喷洒后若遇阴雨天,应补喷一次。喷药时要多喷叶子背面。
Fall cabbage most susceptible to downy mildew, serious years can cut 50-60%. Chinese cabbage was sick, the back of the mold appears mildew, but no obvious positive symptoms of the leaves. After the whole forest was killed, white downy mildew appeared on the back of the leaves and a light green spot appeared on the front of the leaves. Lesions expanded by the limitations of the formation of the veins and polygons or irregular shape, Chinese cabbage into the pericardium, if the environmental conditions fit, the disease developed rapidly, the rapid increase in lesions, the leaves withered. The disease has two peak times a year, the first in late August to early September, the second in late September to early October should catch early. Commonly used pesticides 40% phosphorus aluminum WP 200-300 times, or 80% sodium dextrose 600 times. If the rainy days after spraying should make up spray once. Spray more leaves when sprayed on the back.