Cucumber downy mildew is caused by the infection of Pseudoperonospora cubensis and it is the most serious epidemic of cucumber in protective fields. In the production, a large number of repeated use of various chemical pesticides to prevent and control, although it can receive a certain effect, but due to high pesticide residues, thus posing a threat to the health of consumers. At the same time, due to the increased resistance of pathogens, it is difficult to further control the disease. For this reason, in the long-term work, we have summed up a set of pollution-free techniques for controlling cucumber downy mildew. It is the most economical and effective prevention and control measure to use varieties resistant to downy mildew. The available varieties are Zhongnong No. 7, Zhongnong No. 12, Jinchun No. 3, and Jinza No. 2. Ecological control The so-called ecological control is to create an environment conducive to the growth of cucumber that is not conducive to the occurrence and development of downy mildew. In the absence of drugs, the purpose of reducing and controlling the occurrence and development of diseases can be achieved by controlling the ecological environment. The optimum temperature for the incidence of cucumber downy mildew is 16-24 °C, and the optimum relative humidity is 85% or more. Temperatures below 15°C or above 30°C, the disease is inhibited. The relative humidity of the air is between 50% and 60%, and the bacteria cannot produce sporangia. According to these characteristics, the following control measures may be taken: 0.5-1 hours of air release in the morning, and the shed will be closed after exhausting moisture. In the morning, the temperature is increased to 28-30 °C (not to exceed 35 °C) to facilitate the assimilation of cucumber and inhibit the occurrence of downy mildew. In the afternoon and afternoon, the temperature was lowered to 20-25°C, and the relative humidity of the air was reduced to 60%-70%. When the temperature was lower than 18°C, the shed was closed. In the evening, let it be released again for 2-3 hours. If the outside night minimum temperature reaches 12°C or more, you can let the air out overnight. On cloudy days and rainy days, it is necessary to let the wind down and dampen properly. Strengthen management (1) Use drop-free film. The drip-free membrane has the advantages of no drip, heat preservation, light transmission, and aging resistance, and the dripless membrane can reduce the humidity in the protection floor and improve the light conditions so as to achieve the purpose of prevention and control. (2) Full coverage of the mulching film can increase ground temperature and promote growth. More importantly, it can reduce air humidity and control the occurrence of diseases. (3) Underwater irrigation under small film. Winter should reduce the number of watering. Do not flood the irrigation, should be poured under the membrane of small water. The irrigation time is appropriate for sunny days and it is not suitable for irrigation on cloudy days and early evenings. After the water is turned off, the greenhouse is closed, the temperature is increased to about 35°C, maintained for 1 hour, and the air is evacuated to remove moisture. (4) Short-term high-temperature boring sterilization. When the disease is severe, the shed can be closed at noon on sunny days, so that the temperature near the growing point of the plant rises to 43°C. At this time, the timing begins and lasts for 2 hours. It should be noted that the temperature should not fall below 42°C and 46°C. The day before the drapery, we must pour water once. This treatment can control the disease 7-10 days. Chemical control can use high-efficiency, low-toxicity and low-residue pesticides for prevention and control when necessary. It is strictly prohibited to use highly toxic and high-residue pesticides. The pesticides that can be used are: 74% chlorothalonil wettable powder 600-800 times, 58% thiram Mn-Zn wettable powder 500 times, 72% Kelu wettable powder 600-750 times liquid, 72% frost Epidemic cleansing WP 800-1000 times and so on. The above-mentioned several kinds of pesticides should be used alternately to prevent germs from producing resistance.
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