Cucumber downy mildew is commonly known as horse running, black hair or rickets. It is the most serious epidemic disease in the national protected area and open field cucumber. Cucumber can be affected throughout the growth period. It is characterized by rapid emergence, rapid spread, and serious disease. It can kill most of the leaves in a week or more, causing severe reduction in production and even harvest.
--- First, symptom recognition and disease conditions
--- (I) Symptom recognition Mainly infecting leaves. At the seedling stage, the cotyledons showed irregular fading green macula on the front and gradually yellowed. A gray-black mold layer is produced on the leaf back when wet. In the adult stage, the disease begins to spread upward from the middle and lower leaves, and the leaves are water-stained spots, which gradually expand from yellow-green to light brown. In the wet condition, the surface of the leaf on the back of the leaf is densely grayish black mold layer. In severe cases, the lesions merge into a piece and the whole leaves die.
--- (B) the disease conditions Downy mildew is caused by fungi, the pathogens mainly rely on airflow to spread. High humidity is an important condition that occurs when the leaf surface has water droplets or water film, and the spores can germinate and invade. The optimal temperature for onset is 16 to 24 degrees, and the optimum relative humidity is 85% or more. The temperature is below 15 degrees or above 30 degrees and the disease is inhibited. The relative humidity of the air is below 50% to 60%, and the bacteria cannot produce sporangia.
--- Second, comprehensive prevention measures
--- Prevention and control of cucumber downy mildew should be based on agricultural control, ecological control as the focus, and chemical control as an auxiliary comprehensive measure.
--- (1) Agricultural control
--- 1. Selection of resistant varieties The resistance of different vegetable varieties is different. The selection of cucumber varieties with strong resistance to downy mildew is the most economical and effective control measure. At present, the varieties to be protected are: Zhongnong No. 7, Zhongnong No. 8, Zhongnong No. 12, Zhongnong No. 13, Zhongnong 202, Zhongnong 203, Jinchun No. 3, Jinza 2 and so on.
--- 2, cultivating disease-free and strong seedlings Nursery room and production greenhouse or greenhouse isolation, to avoid seedling infection. Seeds should be sterilized by 50 degree warm water soaking, and the seeding tray should use sterile soil. In the seedling stage management, pay attention to cold insulation, humidity control is below 60%, and the melon seedlings are difficult to develop as long as they do not condense. It is found that the sporadic disease plants should be removed immediately, and the weak and weak seedlings should be strictly eliminated when planting, and the growth and development of strong seedlings should be selected.
--- 3, in the protection of high temperature shacks in order to completely eliminate the bacterial source of bacteria, in the summer and autumn, the use of facilities idle period, the use of closed greenhouses, greenhouse measures, select sunny high temperature shack for about a week, so that the highest temperature in the protected area 60 degrees, can kill germs. Stuffed shed ~ deep turn soil ~ shack. Repeat 1 or 2 times to make the sterilization complete.
--- 4, the rotation of the same crops and the continuous cropping of vegetables lead to serious disease, so in the production can be used in different families of vegetable rotations, reasonable arrangements for gargle.
--- 5, rational fertilization, scientific watering In the preparation of the land, the application of mixed farmyard manure and phosphorus and potassium fertilizer, so that the plant does not lose fat and premature aging in the later stages of growth. If the melon is weak or the leaf color is light, the foliar fertilizer should be applied (such as polyamine liquid fertilizer or plant health 500 times liquid). After pouring the planted water for about 7 days, do not water, and reduce the seedling to the flowering period to control a small amount of topdressing and watering. The irrigation is carried out in the sunny morning, after which the shed can be closed, the room temperature is raised to about 30 degrees, and the air is kept for 1 hour and then the air is discharged. The temperature is lowered to 25 degrees or less, and then the temperature is raised once and then released, and the disease prevention effect is better. .
--- 6. Clean the pastoral In the production, every other week, remove the weeds in the greenhouse or greenhouse, and remove the diseased leaves. After harvesting, all the vegetable residues, leaves and weeds are removed in time and thoroughly, all the hosts of the germs are removed, the breeding grounds are cleaned, and the source of sterilization is reduced or eliminated.
--- (2) Ecological control
--- The so-called ecological control is to create a condition conducive to the growth of cucumber is not conducive to the development of downy mildew, and to reduce and control the disease by controlling the ecological environment without the use of medicine.
--- 1. Selecting no drip film Because no drip film has the advantages of no dripping, heat preservation, light transmission and aging resistance, the use of no drip film can reduce the humidity inside the protection zone and improve the lighting conditions, thus achieving the control effect.
--- 2, hanging hang reflective screen The north side of the greenhouse spine hangs the reflective screen, which can enhance the light, increase the temperature, reduce the humidity (the general temperature is increased by 1 to 2 degrees, the relative humidity of the air is reduced by 3% to 4%).
--- 3, the use of under-drip irrigation technology in winter should reduce the number of watering, avoid flooding. Therefore, with the mulch film covering, it is best to use irrigation techniques such as drip irrigation under the membrane, pipe pouring, and infiltration in the greenhouse, which can reduce the indoor humidity and increase the soil temperature.
--- 4, timely adjustment of indoor temperature and humidity In the morning, the first release of wind for 0.5 to 1 hour, after the discharge of moisture, closed the shed. In the morning, the temperature is raised to 28 to 30 degrees (note that it cannot exceed 35 degrees), which is conducive to the assimilation of cucumber and can inhibit the occurrence of downy mildew. At noon, the temperature dropped to 20 to 25 degrees, the relative humidity of the air dropped to 60% to 70%, and the temperature was lower than 18 degrees. In the evening, the wind will be 2 to 3 hours, which will reduce the water spitting at night. If the minimum temperature outside the night reaches 12 degrees or more, you can release the wind all night. On cloudy and rainy days, the wind should be properly released.
--- 5, short-term high temperature shed sterilization using the downy mildew pathogen spores at 30 degrees above the slow activity, 43 degrees above the activity and gradually die, when the disease is fierce, you can close the shed at noon on sunny days, so that The temperature rises to 43 degrees near the plant growth point and starts counting for 2 hours. At this time, the temperature should not be lower than 42 degrees, nor can it exceed 46 degrees. The shack requires a high humidity inside the room, and the previous day, the cucumber should be poured with a large amount of water. Handle a controllable disease for 7 to 10 days.
--- (3) Chemical control
--- 1, fumigation method The use of this method in the protection of the land to save time, labor, labor, use 40% chlorobacteria before the onset of disease, the amount of 200 ~ 250 grams per 667m2. In the evening, when the work was completed, the bactericidal agent was placed in 5 parts, and it was ignited from the inside to the outside. The shed was sealed and the next morning was ventilated as usual. Generally, it is smoked once every 7 to 10 days, and it is smoked 5 to 8 times. It can also cure powdery mildew and anthrax.
--- 2, dusting method Cucumber adult stage, with 5% chlorothalonil dust or 5% anti-mold powder dust spray. Spraying powder is not only low in cost, but also simple in method, and does not increase indoor humidity when it is not vented in winter. The dosage of each 667m2 is 0.75~1kg, and the powder is sprayed with a harvest type 5 or 10 type duster, usually 3 to 10 days. During the operation, the powder spray pipe is lifted horizontally, and one end of the walkway of the shed is retracted for scattering. The Type 5 duster is about 36 rpm and the Type 10 duster is about 52 rpm. When the powder is sprayed, the shed should be sealed. After one hour of spraying, the air can be ventilated, and the evening work can be closed for one night.
--- 3, spray method In the early stage of the disease can spray 75% chlorothalonil wettable powder 600 ~ 800 times liquid, or 58% toxic mycelium manganese zinc wettable powder 500 times liquid. Pay attention to the alternating use of various pesticides to prevent the development of drug resistance and improve the control effect.
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