Downy mildew, commonly known as “running horse stemâ€, is the main disease affecting cucumber yield and quality in greenhouse cucumber production. In the cultivation and management, we must strengthen the cultivation and management as the main, and supplement the chemical pollution prevention and control technology, we can achieve better control effect.
First, the harm symptoms
Downy mildew mainly damages cucumber leaves. In the early stage of disease, there were yellow and green spots on the surface of the leaves, which gradually expanded to form polygonal yellow-brown patches by the veins. The disease spread from the bottom to the top, and the whole plant died when it was severe. When the humidity in the shelter is high, the Minister of Backstain Disease produces a gray moldy layer.
Second, strengthen the cultivation and management
1. Reasonable rotation: Since the initial infection source of this disease is the downy mildew of open cucumber or the residual diseased organism in the soil, it is advisable to use the summer radish and bitter gourd in the former crop and avoid continuous cropping.
2. Selection of improved varieties: high-quality hybrids with strong disease resistance, high yield, and suitable for cultivation in greenhouses should be selected, such as Jinyou No. 2, Jinza No. 3, and Jinchun No. 4 and so on.
3. Cultivate strong seedlings: Separate the seedbed from the production greenhouse and disinfect the bed soil, strictly control the planting density, strengthen the seedbed management, promptly ventilate and ventilate the water, enhance the light, control the seedlings and grow long, and cultivate disease-free and strong seedlings. Before colonization, 75% chlorothalonil wettable powder 500 times solution can be sprayed to colonize the diseased plants, completely eliminating sick and weak seedlings.
4. Canopy disinfection: 10 days before the cucumber colonization, the first time after the hermitogenesis, the hermitic shed was sealed for 5 to 7 days, and the high temperature was used to kill the pathogen in the shed.
5. Formulated fertilization: Prepare 6,000 kg of organic fertilizer per acre. Accumulate the film two months in advance. After fully fermenting and decomposing, apply 30 kg of urea, 15 kg of diammonium phosphate, and 50 kg of potassium sulfate as base fertilizer. The melon period combined with subsurface dark irrigation was divided into 3~4 times with nitrogen topdressing. In the middle and later stages of cucumber growth, spraying 0.5% urea, 0.2% potassium dihydrogen phosphate, and 0.5% white sugar mixture on the leaves can rapidly increase the total sugar and nitrogen content in the green functional leaves and increase the physiological resistance of the leaves.
6. Control the temperature and humidity in the shed: To control the temperature and reduce the humidity as the center, it is required that the time when the cucumber leaves do not form condensation or condensation should not exceed 2 hours.
Third, add carbon dioxide
After the sunrise, carbon dioxide gas fertilizer is added, so that the content of carbon dioxide in the air in the greenhouse is kept at 1000-1500 mg/kg in sunny days, and kept at 500-700 mg/kg in cloudy days. This allows the green functional leaves to maintain vigorous photosynthesis. Reduce and reduce the incidence of downy mildew.
Fourth, chemical prevention
In the seedling stage and the early stage of disease, use 100 billion live spores/gram of Bacillus subtilis wettable powder 2000~2500 times spray, or use 45% chlorothalonil smoke agent 200~250 grams per acre in the evening after closing the shed Prevention. When the humidity in the greenhouse is large, use 5% chlorothalonil dust 1 kg powder to prevent and control per acre. When the greenhouse is warmed up during the sunny morning, it can be sprayed with 40% triethylphosphonate wettable powder 200 to 250 times spray.
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