黄瓜霜霉病是高寒林区塑料大棚栽培黄瓜的主要病害之一。近两年因当地气候异常,气温变化大,6、7月份降雨偏多,使此病流行蔓延较快,1986年有5％的菜农因没有及时进行防治,半月之内造成整个大棚黄瓜蔓全部枯死、绝产。根据近几年来的观察,发现温室的黄瓜秧苗在3—5片真叶时就开始发病。一般先从下部叶片开始,以后逐渐向上蔓延。病叶初呈淡黄色小斑点,扩大后由于受叶脉限制成为多角形、淡褐色病斑,潮 Cucumber downy mildew is one of the main diseases of cucumber cultivation in plastic greenhouse in the cold forest area. The past two years because of the local climate anomalies, temperature changes, rainfall in June and July, so that the spread of the epidemic is rapid, in 1986, 5% of farmers because there is no timely prevention and control, causing half of the entire greenhouse cucumber vine Death, abortion. According to the observations in recent years, it has been found that the cucumber seedlings in the greenhouse start to develop when they are 3-5 true leaves. Generally start with the lower part of the leaves, then gradually spread upward. Sick leaves at the beginning of small yellowish spots, enlarged due to the limitations of the veins become polygonal, light brown spots, tide