Recently, the continuous haze weather in North China has caused weak sunlight and low temperature in the vegetable greenhouse, which has become a key factor affecting the growth of vegetables. Many vegetables have problems such as yellow leaves, dry tips, rot at growing points, retting of roots, falling flowers and fruits, and serious diseases. In this regard, the protection of vegetables should be managed by the following measures.
1. Keep seedlings of existing vegetables in the greenhouse. In the greenhouse during the day, as long as the temperature reaches above 18°C, a short period of time (about 20 minutes) of ventilation can be carried out, and there is no dew on the leaves, the pesticide can be sprayed, and silicone additives should be added to improve the absorption and utilization of pesticides. Take cucumbers and tomatoes as examples, to control downy mildew, blight, and gray mold, spray 60% Biotide + 5% Zhongshengmycin + 72% agricultural streptomycin, and use 5% chlorothalonil every 2 to 3 days. Smoke agent or 10% Sukeling smoke agent, airtight fumigation at night to reduce the occurrence and development of diseases. Do not water the vegetables that need to be watered on cloudy days. Instead, spray foliar fertilizers to supplement nutrients, and then water them after sunny days. The cucumber that forms the "flower topping" can be properly thinned, the yellow leaves are removed and taken out of the house, and sprayed or fumigated in time to reduce the occurrence of wounds and diseases caused by manual removal of leaves.
2. Management after continuous cloudy and sunny days. The phenomenon of retting is prone to occur after continuous cloudy days for more than 5 to 7 days. In some areas, the haze days are more than half a month. Most vegetable roots have varying degrees of rusty roots, and there are almost no white roots that can absorb nutrients. If there is a half cloudy and half sunny weather, the temperature will gradually rise, and the damage to the seedlings will be less. If it is suddenly sunny, corresponding measures must be taken. (1) When the temperature in the shed rises to 23℃, start to ventilate, spray white sugar + vinegar (50 grams each) to dilute 150 times when the leaves are smashed, or spray foliar fertilizer and sugar on the leaves to increase the air humidity to slow down the smashing phenomenon. When the temperature rises above 26°C, wilting occurs again and the grass thatch can be covered, covering 2/3 of the shed surface. When the seedlings return to normal, the grass thatch can be rolled up in time. On the second day, observe the performance of the seedlings. If there is still wilting, spray chlorothalonil + streptomycin + brassinolide to reduce the occurrence of diseases and promote rooting of the seedlings. (2) When the seedlings need to be watered, suddenly do not water them on sunny days. When the 10 cm ground temperature rises to above 16°C, water the seedlings and try to increase the ground temperature. (3) Raise the ground temperature. After a sunny day, as long as the seedlings do not wilt, let a small breeze at about 23°C in the morning, close the air outlet when the temperature drops by 1.5°C to 2°C, and ventilate again when the temperature rises above 28°C. If it is sunny in the morning after ventilating at 23°C, the temperature will only drop by 1°C to 1.5°C, and it will not take a long time to rise again. There is no need to shut off the air outlets, but when the temperature reaches 30°C at noon, increase the air volume. In the afternoon, when the temperature drops to 25°C, turn off the air outlet. If the temperature rises 1°C to 2°C, it will help increase the ground temperature, store heat, and benefit the growth of roots.
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