Cucumber downy mildew, also known as “horse racing†or “fire dragonâ€, is one of the most common diseases in cucumber production. Its onset is characterized by fierceness, rapid spread, and severe disease. If it is not controlled in time, it can cause severe reduction in production.
Symptoms: When the onset of disease, there are spots of light yellow spots on the back of the leaves. After the enlargement, there is a yellowish-brown spot that is limited by the veins. When the moisture is on the back of the lesions, a layer of grayish black mold grows; when the humidity is high, the diseased leaves Decay, mostly from the middle and lower leaves began to spread upward, in serious cases can cause the whole plant withered to death.
Incidence conditions: The occurrence of downy mildew is associated with high temperature and humidity, low field light transmittance, and poor air permeability. Under normal circumstances, the temperature is 16-24°C, and the relative humidity of air is more than 85%, which is most suitable for its occurrence.
Control methods:
First, choose cucumber varieties that are resistant to downy mildew.
Second, strengthen field management:
(1) The use of plastic film covering technology can effectively reduce air humidity;
(2) The diseased leaves and yellow leaves of the old leaves are promptly found and removed, taken out of the field, and buried or destroyed.
(3) Scientific fertilization and watering, increase the application of organic fertilizers, avoid flood irrigation, cloudy irrigation water.
Third, chemical control:
Adhering to the principle of "prevention as the mainstay and comprehensive prevention and control", we must use protective fungicides, such as mancozeb and chlorothalonil, every 5-7 days before the onset of disease to detect the diseased leaves and diseased plants of downy mildew. After the treatment with a therapeutic bactericide, such as Jin Lei, Ami Xida, DuPont Kelu, Baitai and other fungicides for spray control, no leakage, no heavy spray, spray thoroughly spray.
Fourth, ecological control:
According to the rise and fall of temperature, regulate the temperature and humidity in the shed to prevent and control the occurrence of diseases.
1. When the average temperature on the day is below 10°C (at this time, the temperature is low and it is not suitable for downy mildew), pay attention to warming and heat preservation, use less ventilation during the day, close the shed early in the evening, and not ventilate at night, so that the temperature inside the shed can reach 32 during the day. °C, the ground remains moist.
2. When the average temperature on the day is stable at 10~13°C, the temperature and humidity in the shed shall be adjusted flexibly according to changes in day and night temperature.
3. When the minimum daily temperature is 13 to 15°C, the air can be released overnight.
4. When the daily minimum temperature exceeds 15°C and the temperature in the shed is difficult to reduce, the disease can be controlled by reducing the humidity. At this time, the air can be released overnight, and the irrigation should be performed at a low temperature in the morning. After irrigation, the shed is closed and the temperature of the shed is raised to 30°C and then the air is discharged again.
Through the above management of the temperature and humidity in the shed, it is possible to create an environment suitable for the growth of cucumber which is not conducive to the germination of pathogens, so as to achieve the purpose of suppressing the spread of diseases.
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