Cucumber cultivation in greenhouses is a common and frequently occurring disease. Once it occurs, it can lead to a significant reduction in yield, and even no harvest. The symptoms of the disease are easily confused with cucumber downy mildew, and farmers are not easy to identify, it is easy to prevent timely symptomatic control.
Symptom recognition
Cucumber can reach the stage from the seedling stage to the adult stage, and it mainly damages the leaves, petioles, stems, melons and other parts of the cucumber. At the onset of seedling stage, round or semi-circular brown spots are formed on the cotyledons, which are slightly sunken and dry at the later stage. In the adult plant stage, water-stained round chlorotic spots appeared on the leaves. After being slightly expanded, the leaves were limited to polygonal brown spots and surrounded by yellow halos. In the wet, the back of the lesion overflowed with white bacteria and pus, and the lesions were dry and cracked to form a perforation. In severe cases, the melon strips will also be infected. The leaves or melon strips near the ground will be the first to develop and spread upwards. The melon strips will initially appear as water-stained, nearly circular, pale gray lesions that turn into light brown. In wet conditions, the diseased part may also produce milky pus; the stalks of the stalks will be damaged. In severe cases, the seeds will be rotted and smelly. After drying, they will be milky white and leave fissures. In severe cases, the melon strips will rot and fall off early.
Cucumber bacterial angular spot disease, its early symptoms and cucumber downy mildew is very similar, should be carefully differentiated. Cucumber downy mildew mainly damages the leaves. In the back of the polygon lesions will grow villous purple-gray to purple black mold layer, no mucus on the leaves; If planting high resistance to downy mildew varieties, lesions were nearly elliptical or nearly round Shape, while lesions are not perforated (no holes). If the symptoms of the two diseases are indistinguishable, 1-2 leaves can be picked, washed with clean water, placed in a clean plastic bag, and sealed at a suitable temperature for 24-48 hours to check the lesions on the back of the leaves. Department, such as the emergence of white bacteria pus for the bacterial keratoses, such as the emergence of black mold layer is downy mildew; sometimes there are some white pus bacteria lesions, and some black mold layer, by the performance of bacterial angular spots Disease and downy mildew occur simultaneously.
Infection cycle. Cucumber bacterial angular spot is a bacterial disease caused by a bacterium called Pseudomonas spp. The bacteria spread over the winter on the seed or in the soil of the diseased body. Bacteria in the soil spread by splashing as they flood. The newly produced bacteria are transported by wind and rain, agricultural operations, and insects. The bacteria invade the host from wounds, stomata, and water holes. Hazardous. When the air humidity in the field reaches more than 75%, the disease begins when the temperature is above 18°C, the humidity is 85%-95%, the incidence is the heaviest when the temperature is 18-25°C, the epidemic is fast; the humidity is less than 70%, the temperature is lower than 18°C, or Temperature is higher than 35 °C, less than 12 °C is not easy to disease. In hot and rainy, low-lying areas at the water, many years of continuous cropping, fertilizer and water management is not strict, especially in poor ventilation in greenhouses to make the humidity is too large, the resulting fog on the leaves condensed into a water film or droplets, then easy to disease. Flooding with excessive irrigation or excessive watering and cloudy watering can easily cause high-humidity environment and cause morbidity. When the pursuit of economic benefits is too dense, it is easy to cause morbidity and increase the risk.
Prevention
Agricultural control. 1. Selection of disease-resistant varieties, such as Jinchun No. 1, Jinyan No. 4, Jinyou No. 30, and Jinza No. 2 etc., have strong disease resistance, and show resistance to diseases, high quality and high yield. 2. Seed disinfection. Soak the seeds in warm water of 50°C for 20 minutes, then remove them and put them in cold water for 4-6 hours, then sow germination. 72% agricultural streptomycin 3000-4000 times solution can also be used for soaking 2 hours or soaking with 40% formaldehyde 150 times for 90 minutes, germination after rinsing with water, can play a role in disinfecting the seeds. 3. Reasonable rotation. Several main varieties of various vegetables should be cultivated in a reasonable rotation, changing crops and planting, avoiding continuous cropping in the same family, and the implementation of rotation for more than two years can greatly reduce the amount of bacteria in the soil, so that the damage to the light spot disease is lighter. . The use of disease-free pest-raising seedlings and high-covered film cultivation, the best seedlings in the field, to ensure seedlings are not sick, and at the same time when planting high-covered film cultivation is better. 4. Scientific fertilization. Increase the use of organic fertilizer, promote the use of microbial fertilizers and compound fertilizers, make the ratio of nitrogen, phosphorus and potassium reasonable, in order to improve the resistance to disease. Vigorously promote the use of special fertilizers for pollution-free production to enhance the comprehensive disease resistance of cucumbers. 5. Pay attention to temperature and humidity. The implementation of scientific control, strict regulation of temperature and humidity, and avoiding the appearance of water film on leaves, is the key to disease prevention in greenhouses. Reasonable regulation and control experience is: timely and reasonable ventilation, so that the greenhouse temperature and humidity in the morning relative humidity 65% ​​-75%, temperature 25-30 °C; night relative humidity 80% -90%, temperature 15 °C or less. Often by adding phosphorus and potassium fertilizers, spraying nutrient solution and other measures to add nutrients in a timely manner: First, combined with watering, with water flushing 5%-8% of the special fertilizer solution for vegetables; Second, spraying 0.2% -0.3% of the Potassium dihydrogen phosphate solution. 6. Physical control. At the beginning of the disease or when the disease is severe, choose fine weather. Water the cucumbers in the morning and close the greenhouse at noon. Raise the temperature of the shed to 44-46°C and continue for 2 hours. Then slowly ventilate and cool the water. Repeated 5-7 days to kill the bacteria and promote the lesion "calcification."
Chemical control. In the early stage of onset of disease prevention and control, the available effective agents are: 72% of agricultural streptomycin 4000 times; neemectin 4000 times; 50% DT bactericide 800 times; 60% DTM WP 500 times ; 50% green WP 500 times; 27% copper high suspension 400 times, spray. Or use 50% garnet copper WP wettable powder 500 times, or 14% urinary ammonia copper water bath 300 times, or 77% copper hydroxide wettable powder 400 times, or 72% agricultural streptomycin sulfate soluble Powder 4000 times spray control. When bacterial leaf spot and downy mildew occur at the same time, it can be controlled by 47% spring thunder-copper WP, 50% sulphouric copper wettable powder and water spray. Note that the spray should be uniform and the back of the blade should be sprayed. When a large amount of wounds appear in the plant when the greenhouses are in operation, all fields shall be sprayed in time to avoid invading bacteria.
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