From June to August each year, the leek in Beijing enters the summer raising period. Amaranth disease is the main disease in the cultivating period. The roots, stems, leaves, flower buds and other parts of the leeks can be harmed, especially the pseudo-stems and bulbs are the most seriously damaged. When the root is damaged, it becomes brown and rot, the root hair is obviously reduced, and the life of the root is shortened. When the pseudo stem is damaged, it is light brown, water-soaked soft rot, the leaf sheath is easy to fall off, and the sparse gray-white mildew layer is visible when the air is wet. When the bulb is damaged, the root plate is water-soaked, light brown to dark brown rot, the internal tissue of the bulb is light brown, and the new leaves are delicate. The disease of leaves and flower buds starts from the middle and lower parts. It is a dark green water-immersed lesion with a length of 0.5-5 cm. The disease is collapsed after the water is lost, causing the leaves and stalks to sag vertically to decay. When the humidity is high, the white mold is visible. .
The pathogen of amaranth is a genus of Phytophthora, which can invade a variety of vegetables such as onion, garlic, eggplant, tomato, etc., and the mycelium or chlamydospores are overwintered in the soil with plant residues, and sporangia and zoospores are produced when conditions are appropriate. After the initial infection is formed and the humidity is increased, the spores are released from the diseased part, and the spores are released by the wind and rain, and the farming operation spreads to form repeated infections. The optimum temperature in the field is 25 °C-32 °C, the humidity is increased, and the incidence is aggravated. The Beijing area generally begins to develop in early July, enters the prosperous period in late July, and peaks in the first half of August. After the heavy rain, there is a peak incidence. Continuous cropping, field water accumulation, partial application of nitrogen fertilizer, and poor ventilation can cause the disease to occur.
Prevention and Control Measures
1. The plant residues after harvesting should be removed in time to keep the pastoral clean; during the raising of larvae, the old leaves and weeds should be removed in time to improve the ventilation and light transmission capacity. The above-mentioned impurities can be treated in a harmless manner in time, and a solar ozone agricultural waste treatment station, a mobile ozone agricultural waste treatment vehicle, or a centralized deep-buried, waste shed film high-temperature closed stack can be used for harmless treatment.
2. Avoid continuous cropping with onion and garlic crops, eggplant and tomato, and implement 2-3 years of rotation.
3. Carefully level the land, repair the drainage system in the field before the rainy season, and remove the water in time after the rain.
4. Pay attention to rooting, do not over-harvest, remove flower buds in time, and rationally apply fertilizer after harvesting, avoid partial application of nitrogen fertilizer and control irrigation.
5. The seriously ill plot should be removed from the lower yellow leaves before the rainy season, and the green leaves should be lifted up and fluffed to avoid the stalks contacting the ground and reducing the occurrence of diseases.
6. In the early stage of the disease, use 72% frost urea·manganese zinc wettable powder 600-800 times solution, or 69% enoyl manganese zinc wettable powder 600-800 times solution, or 72.2% creamer hydrochloride hydrochloric acid 600 solution. -800 times liquid, or 58% metalaxyl · manganese zinc wettable powder 500 times liquid and other agents spray, once every 7 days, continuous control 2-3 times. In addition to spray application, the root solution can also be used at the beginning of the rainy season.
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