Cucumber downy mildew
Cucumber downy mildew, commonly known as "black hair" and "running horse stem," is the most important chronic disease of cucumber. Inadequate prevention and control can cause serious losses. In addition to destroying cucumbers, the disease also harms wax gourds and loofahs.
Symptoms The disease mainly affects the leaves, tendrils, vines, and pedicels. At the beginning of the leaves, water spots were formed on the back of the leaves. Afterwards, the lesions gradually expanded. Due to the limitation of the veins, they were polygonal and water-stained. When wet, there is a layer of purple black mold on the lesion. The early lesions of the leaves were yellow in color and their edges were not obvious, and they turned yellow-brown afterwards. In severe cases, the lesions were contiguous, and the whole leaf curled and dried. Only the leaves were observed.
Pathogen? Pseudoperonospora cubensis (Berk et Curt. Rostov) is a flagellin-borne subphylum fungus.
The characteristics of the disease?? Pseudoperonospora cubensis is an obligate parasite. In the areas where cucumbers were cultivated in the year, the pathogenic bacteria in autumn was transmitted from the open air to the protected cucumbers. In the spring, it was passed from the protected area to the cucumbers in the open field. It began again and again year after year. However, in areas where cucumbers are not grown during the winter, it is unclear where and how wintering sites and methods are used. Humidity is a determinant of the occurrence of the disease. When the temperature at 16 ~ 20 °C, relative humidity of 85% or more, especially leaves with water droplets or water film, the fastest invasion of bacteria.
Control methods
1. Selection of disease-resistant varieties such as Jinyan No. 2 and No. 4, Jinza No. 3, Hu No. 5 cucumber, Shanghai No. 58 cucumber, Baoyang No. 5, Yangyao cucumber, Collaboration No. 17, Baoza No. 2, Baoza On the 3rd, Zhongnong 5 and so on. Mycteria species are not resistant to disease but have the advantages of early maturity and high yield.
2. Agricultural control applies base fertilizer, applying organic fertilizer 5000 kg per mu, soaking the bottom water, cultivating disease-free strong seedlings; timely pod-type transplanting, mulching film, under the film pouring dark water; regular fertilizer, timely removal of disease leaves Yu Tian Deep buried outside.
3. Ecological Prevention and Control The protected land uses the environmental conditions that are conducive to the growth and development of cucumbers to inhibit germs and achieve the purpose of preventing and controlling diseases. The first is to change the time of watering, sunny morning or morning watering, after pouring closed shed heated to 33 °C for 1 hour after the release, repeated 2 or 3 times. The second is the scientific release of the air, strict control of humidity and temperature. The daytime temperature in Daejeon should be maintained at 25 to 30°C. When it is higher than 31 to 32°C, the wind should be released and the wind must be opened first. In the autumn and spring, when the temperature is high, the waist or back wall wind is combined. Night temperature 11 ~ 13 °C, relative humidity of 75% ~ 80% during the day, is conducive to photosynthesis of cucumber. Relative humidity of 80% to 85% at night can reduce nutrient consumption and inhibit the invasion of bacteria.
4. Pharmacy control? Strengthen the field disease investigation to master the dynamics: Before the disease enters the initial stage, when the dew is not yet dry in the early morning, check the water-soaked central disease plant for 5 to 7 days, or a large number of water-soaked lesions. After 1 or 2 days, the lesions of the reference blade developed from a flooded shape to a polygonal shape, the layer of downy layer appeared on the back of leaves, and the future weather turned negative or heavy fog, dew, and rain were reported. period.
In the disease after the first 3 to 5 days of medication, medication interval of 7 to 10 days or so, 3 to 5 times in a row, serious illness in the field as the disease develops, if necessary, can also increase the number of spraying. In the early stage of the disease, the therapeutic agent can be used as follows: 72% Kelu wettable powder 1000 times liquid (100 g/mu); 69% Anke manganese zinc wettable powder 1000 times liquid (100 g mu); 52.5% faster Water purification dispersible granules 2000 to 3000 times liquid (amount of 40 to 50 grams of mu); 58% Lei Duo Mier - manganese zinc wettable powder 1000 times (100 grams of mu dose) and other spray. Preventive control before the onset of disease can use Dasheng M-45 WP 800 times the liquid (mu of 125 grams); 40% of Dakkoning suspension 600 times (mu of 165 grams); 56% of the wettable powder 600 ~ 700 Times of fluid (mu amount of 150 ~ 200 grams); 80% of Shan Desheng WP powder 600 ~ 800 times (150 ~ 180 grams per mu dose); 77% can kill WP 1000 times liquid (100 grams per mu dose); 64% anti-microbial ultra-wettable powder 1000 times (100 grams per mu) spray.
Before the onset, 5% chlorothalonil dust may be used, 1 kg per mu, sprayed once every 9 to 10 days, or 45% chlorothalonil smoke agent, 250 kg per mu, smoked once every 7 to 9 days. The fume smoke began when the shelter was closed in the evening and was released early in the morning the next morning. The agents should be used alternately to increase the control effect and delay the development of resistance.
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