Chives, also known as chives on all four seasons, are one of the indispensable spices in the kitchen due to its soft texture and spicy smell. They are also the main varieties of dehydrated vegetables. There are often various diseases in cultivation, and downy mildew is the main disease that often occurs. It often results in the loss of edible or commercial value of onion leaves, which has a great impact on the yield and benefits, and even severely destroys them. Because the symptoms are similar to gray mold, the diagnosis process is easy to confuse, which brings certain difficulties to the prevention and control work. The pathogenicity and control methods of chive downy mildew are briefly described below. First, the symptoms of onion downy mildew mainly damage the leaves. When the seedlings grow to 5-6 leaves, about 17 cm high into the long-term when the onset of disease. First from the middle of the outer leaf or tip of the disease, up and down or spread of the heart and leaves. The surface of the diseased area was covered with grayish or brownish-brown layers, and the diseased and healthy borders became indistinct, gradually turning yellow-green, and finally grayish green and dry. The middle part of the leaves became infected, and the diseased part gradually drew and drooped or died from the disease. When the damp leaves are rotted, the rain falls on the soil surface of the rhizosphere and shrinks and twists after drying. Frequently mixed with purple spot. Second, the pathogens and the occurrence of the law downy mildew is caused by flagellin sub-door damage caused by Pythium infestans. The suitable temperature for the growth and development of pathogenic bacteria is 10-15°C. The number of sporangia formed below 20°C below 10°C is significantly reduced; and the sporangia below 3°C below 27°C does not germinate. The oocysts are overwintering with the diseased body in the soil or seed, germinate in the following spring, and cause disease from the invading of the plant's stomata, or latent in the bulb seedlings with mycelium, and the mycelium expands with the growth of the cotyledon. After the onset of the disease, a large number of conidia were generated on the lesions, and transmitted through wind, rain, insects, etc., and invaded many times. It is generally planted too early, soil is heavy, drought is dry, and the terrain is low, drainage is bad, partial nitrogen fertilizer is applied, and the incidence is heavy. Sustained rain, heavy rain, or heavy fog during high-growth conditions are conducive to disease epidemics. Third, the prevention and control methods 1, select the appropriate land planting. Chives are weak in root system and have poor drought tolerance. They should be selected for cultivation with high ground, loose soil, deep soil, convenient drainage and irrigation, and cultivation of crops other than onions and garlic. 2, use disease-free seedlings. Shallots are generally used for bulbs, and seedlings should be kept in disease-free plots in early spring, and then stored dry after harvesting. 3, suitable for planting. After the planting in mid-October, the scallions will avoid the high temperature and rain before the Mid-Autumn Festival and prevent onion seedlings from prolonging and reducing stress resistance. 4, clean the pastoral. During the harvest, the field diseased plant debris was cleaned. During the growing period, the central diseased plant was found to be removed in a timely manner and brought out of the field to be deeply buried or burned to reduce the source of bacteria. 5, strict pharmaceutical soaking. Before the planting, the last seedling selection, after drying, use a mixture of 72% wet mildewed WP or 58% Lydomil wettable powder 1000 times and 72% 10 million units of agricultural streptomycin soluble powder 4000 times liquid Seed soak for 30-40 minutes, air dry and colonize with medicine. After testing, it has a good effect on controlling or preventing disease occurrence without any adverse effects. 6, strengthen management. Apply organic fertilizer, increase potassium fertilizer, enhance plant resistance, and keep the field moist without excessive moisture. 7, prevention and control of good onion fly, thrips, leaf miners, aphids and other insects. 8, spray control. Seedlings up to about 15 cm, spraying precautions can be sprayed, spraying 72% mildew net wettable powder 500 times, 64% antitoxic powder wettable powder 500 times, 7-10 days 1 time; 58% of the initial period can be sprayed Ledomil 500 times, 50% acetaminophen WP 800-1000 times, every 7-10 days, once every 2-3 times.
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