The comprehensive prevention and control of the damage caused by downy mildew in scallion is the key
The onion downy mildew is a fungal disease caused by the downy mildew infection. The disease condition develops rapidly in the field, which can easily cause the onion seedling to die quickly and the yield loss is serious.
The disease mainly damages the onion leaves and flowering branches, and usually occurs when the onion seedlings have 5-6 leaves, the plant height is about 17 cm, and the plants grow vigorously. First on the middle of the outer leaf of the green onion or on the tip of the leaf, extending backwards and spreading to the heart and leaves. After the green onion bulbs are damaged, the diseased leaves of the growing seedlings are gray-green, and when they are severe, the diseased leaves are distorted, yellow, and thickened. When the humidity is high, the surface of the diseased plant is covered with white fungus, and there is no obvious single lesion. This is an important basis for identifying the disease. Diseased leaves are susceptible to discoloration, sagging, breaking, rot, and withering. The early onset of pseudostem prone to scoliosis, the late onset is easy to crack. Usually planted too early, heavy soil quality, drought, lack of water, low-lying terrain, poor drainage, partial nitrogen fertilizer, repeated cropping plots are susceptible to disease. Onion seedlings enter the vigorous growth period, and in case of adverse weather conditions such as continuous rain, heavy rain, fog, dew, and large temperature difference between day and night, the disease becomes popular.
In order to alleviate the damage caused by green onion downy mildew, we should choose the sandy land with high topography, loose soil, deep soil and easy drainage and irrigation to plant green onions. It is not appropriate to repeat the continuous cropping. It should be applied to crops such as broad-leaved vegetables and eggplants. Before sowing, seeds can be soaked in water at 50°C for 25 minutes. After cooling the seeds, they can be sown and then sown. It is also possible to use 50% thiram WP in a 0.3%-0.4% seed dressing. Strengthen nutrient management, re-apply organic fertilizer, increase potash fertilizer, control the amount of nitrogen fertilizer, and enhance plant resistance. Strengthen water management. Water during droughts should be diligently watered to keep the fields moist. Drain the water in time after rain and avoid the accumulation of water in the fields. When onion height is 15 cm, it can be sprayed with 20% fluoxaline wettable powder 1000-1500 times liquid or 10% cyclosulfazolone suspension 1000-2000 times liquid spray. If the diseased plants are found during the growth of green onions, they should be promptly removed. After the harvest, the scallion was cleared of sickness.
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