How should vegetable production respond to low-temperature rain and snow weather?
According to the forecast of the National Meteorological Center, recently, under the combined influence of the eastward-moving southern branch trough and cold air, strong low-temperature and rain-and-snow weather processes have occurred in Southwest China, eastern Northwest China, North China, Northeast China, the Huang-Huai region, Jianghan, Jianghuai and other regions. This temperature drop and rain-and-snow process covers a wide area, but lasts a short time and the temperature drop is small, which is beneficial to the safe overwintering of winter wheat and has little impact on perennial economic crops such as fruit trees and tea plants, but it brings adverse effects on vegetable production, especially protected vegetable production. In order to guide all localities to reduce the impact of disasters, quickly restore production and ensure stable supply, the National Agricultural Technology Extension Service Center and the Vegetable Expert Guidance Group of the Ministry of Agriculture and Rural Affairs have studied and put forward the following technical guidance.
I. Technical measures for preventing low-temperature and snowfall damage to open-field vegetables
(1) Heat preservation and cold protection. For vegetable fields where intertillage can be carried out, when low temperature, snowfall, freezing or a cold wave arrives, soil can be cultivated beside the vegetable roots through intertillage, which can effectively loosen the soil, prevent the root system from being frostbitten, promote root growth and maintain root vitality. Before a cold wave or rain and snow arrives, plastic film, non-woven fabric or shade netting can be used for covering to protect against cold; after the cold wave, covering should continue to be strengthened to delay the freezing and thawing process and prevent vegetables from suffering frost damage.
(2) Dehumidification and waterlogging reduction. In winter, the groundwater level is relatively high. When rain and snow occur, soil moisture increases, and vegetables in the field, especially open-field vegetables, are prone to root rot, dead seedlings and rotten vegetables. Ditches should be cleared and drainage furrows regulated in time to prevent water accumulation in the field.
(3) Strengthening plants. Before a cold wave or rain and snow arrives, measures such as foliar spraying of chitosan, seaweed acid and other full-nutrition foliar fertilizers, as well as plant-derived growth regulators, can supplement the medium and trace elements urgently needed by the plants. This can not only avoid insufficient nutrient supply, but also improve the cold resistance of vegetable plants and reduce the occurrence of rotten vegetables and frost injury.
II. Technical measures for preventing low-temperature and snowfall damage to protected vegetables
In winter, the temperature is relatively low and light is insufficient. When cold waves and snowfall occur, protected vegetables are prone to chilling injury and frost damage, and corresponding measures should be taken in time.
(1) Reinforcing greenhouses. To prevent accumulated snow from crushing the facility structure, the frames of greenhouses should be checked in time, and those with serious steel pipe corrosion or aged and broken bamboo poles should be repaired in time. Greenhouses with poor snow-pressure resistance should have support columns added as early as possible for reinforcement and repair. For solar greenhouses with earth walls, film should be added to the rear roof to prevent snow water from seeping down and damaging the wall.
(2) Strengthening insulation. Cover the outside of the greenhouse with insulation quilts, straw mats and other materials, and add a layer of plastic film to prevent the insulation materials from absorbing water and reducing the insulation effect. Build simple middle tunnels and small arched tunnels inside the greenhouse to form multi-layer covering and reduce heat loss. Add multiple layers of straw mats (curtains) around the greenhouse, on the rear wall and at the base of the greenhouse, which can effectively protect against wind and preserve heat. Set up buffer film at ventilation openings and greenhouse entrances, or use multi-layer covering for insulation.
(3) Preparing for heating. Prepare auxiliary heating items such as bathroom heater heat-conversion bulbs, electric heaters, automatic heating fans, air heating wires, electric hot-air furnaces, emergency heating fuel blocks, fuel-oil hot-air furnaces and stoves, so as to provide temporary heating when a cold wave arrives.
(4) Increasing light. Before rain and snow, clean fog droplets and dust on the greenhouse film in time to ensure the light transmittance of the film; clean old leaves and diseased leaves to increase scattered light between plants; at the same time, hang reflective curtains on the rear wall of the greenhouse. Multi-layer covering and cold cloudy weather can easily lead to insufficient light. Areas with conditions should prepare supplementary lighting equipment such as plant growth lamps, LED lamps, iodine-tungsten lamps and sodium lamps in time, and carry out appropriate supplementary lighting when necessary.
(5) Moderate fertilization. Before a cold wave and rain and snow arrive, increase the application of organic fertilizers, such as pig manure, cow manure and compost and other heat-generating fertilizers; moderately increase fertilizers of medium and trace elements such as magnesium, zinc and boron; quick-acting nitrogen fertilizer should not be applied. Foliar spraying of 0.3% potassium dihydrogen phosphate solution 2~3 times can improve plant stress resistance.
(6) Controlling watering. Watering is strictly prohibited during the low-temperature period before rain and snow, so as not to lower the ground temperature and aggravate chilling injury and frost damage; the principle of “three water and three no water” should be followed, namely water on sunny days and no water on cloudy days, water before noon and no water after noon, water lightly and do not water heavily.
(7) Reducing pruning and branch removal. Avoid plant wounds becoming infected and developing disease under low-temperature and high-humidity conditions.
(8) Low-temperature hardening. 1~2 days before a cold wave and rain and snow, appropriately carry out low-temperature hardening management of plants, with daytime and nighttime temperatures about 2°C lower than normal management, to help vegetable crops adapt in advance to the low-temperature environment and reduce physiological disorders such as flower and fruit drop caused by a sudden temperature drop.
(9) Disease prevention. Before a cold wave and rain and snow, choose sunny weather to spray vegetables with pesticides to prevent the occurrence of diseases. Because spraying liquid pesticides increases humidity in the greenhouse, smoke agents and dust methods should be preferred for pest and disease control. For fungal disease control, 5% chlorothalonil compound dust can be used; for late blight and gray mold, 6.5% wanmeiling dust and 5% shuangkewei dust can be used; for bacterial diseases, 5% zhutong dust can be used; for cucumber downy mildew, phytophthora blight, tomato early blight, late blight and gray mold in greenhouses, 45% chlorothalonil smoke agent can be used, with 250 g per mu each time; for cucumber powdery mildew, 15% procymidone · chlorothalonil smoke agent can be used, with 250 g per mu each time; for vegetable sclerotinia rot, 10% procymidone smoke agent can be used, with 250-300 g per mu each time.
III. Technical measures for disaster reduction after low-temperature snow disasters on open-field vegetables
(1) Garden and field management. After a snow disaster, management of vegetables still in the garden should be strengthened, field snow should be removed in time, and ditches should be cleared, drainage carried out and intertillage performed promptly to reduce soil moisture and reduce the occurrence of waterlogging damage. For some fields with low-lying terrain, long ridges and poor drainage, additional middle ditches should be opened to drain water and remove waterlogging.
(2) Heat preservation and freeze protection. Use various materials to strengthen heat preservation and freeze protection for open-field vegetables. For overwintering open-field leafy vegetables such as green vegetables, celery, lettuce and leaf lettuce, non-woven fabric, old plastic film, straw curtains and shade netting can be used at night for covering and insulation to prevent frost damage. For plastic film covering and insulation, small arched tunnel covering should be adopted; for non-woven fabric covering and insulation, floating covering should be adopted.
(3) Reasonable fertilization. Appropriately apply additional phosphorus and potassium fertilizers. 0.2% potassium dihydrogen phosphate can be sprayed on the leaves to improve plant cold resistance and promote the crops to recover growth as soon as possible.
(4) Timely harvesting. Before and after rain and snow, vegetables that can be harvested and marketed should be harvested and marketed promptly to reduce losses.
IV. Technical measures for disaster reduction after low-temperature snow disasters on protected vegetables
(1) Removing snow. Clean up snow in time. During heavy snow, it should be removed while snow is falling, and special attention should be paid to strengthening snow removal at night. Methods such as spreading snow-melting agents and salt can also be used to quickly reduce the thickness of snow on the greenhouse and prevent the greenhouse from being crushed and collapsing. Areas with conditions can use high-energy lamps and other methods to raise the temperature inside the greenhouse and promote the snow on the greenhouse film to melt and slide off by itself. If it snows during the day, straw mats and other coverings should be opened as much as possible, which not only helps use scattered light to maintain the temperature inside the greenhouse and carry out photosynthesis, but also helps remove snow from the greenhouse in time; if it snows at night, a layer of plastic film can be covered outside straw mats and other coverings, which not only facilitates snow removal, but also effectively prevents cotton quilts, straw mats and other coverings from becoming soaked.
(2) Heat preservation and temperature increase. Set up middle tunnels and small arched tunnels for multi-layer covering, and spread plant ash on the bed surface. Where conditions permit, facilities and equipment such as ground heating wires, electric heating wires, air heating wires, stoves, hot-air furnaces and supplementary lighting lamps can be used to increase temperature. Temperature control measures should be taken according to different vegetable varieties. For melon and fruit vegetables (tomato, pepper, eggplant, cucumber, zucchini, etc.), the temperature must not be lower than 6°C, and must not be lower than 5°C for a short time; for leafy vegetables, it must not be lower than 0°C.
(3) Increasing light. Reflective curtains can be hung and supplementary lighting lamps installed to supplement light; anti-drip agents can also be sprayed to increase film light transmittance. Spray a water solution of flour and bean powder diluted 50-100 times (with a small amount of neutral laundry detergent) on the inner wall of the greenhouse film to achieve an anti-drip effect.
(4) Ventilation and humidity reduction. After snow, coverings should be opened in time for ventilation to reduce air humidity in the greenhouse and increase CO2 concentration. Ventilation should be carried out at noon on sunny days. After opening the coverings, if vegetables are found to be wilting, they should be covered immediately, and then opened again after the leaves recover, repeating several times until they no longer wilt. If wilting is severe, clean water or 1% glucose water or 1% seaweed acid solution can be sprayed on the wilting plants to help restore plant growth as soon as possible.
(5) Timely disease prevention. After snow, vegetables in greenhouses are prone to diseases, and smoke agents and dust agents should be used for control. If gray mold occurs, iprodione, pyrimethanil, dimethachlon, boscalid, chlorothalonil, procymidone, thiram and others can be used for control; if sclerotinia rot occurs, in addition to the above drugs for controlling gray mold, vinclozolin, prochloraz, carbendazim, triadimefon and others can also be used for control. At the same time, straw curtains or non-woven fabric and other coverings should be opened appropriately as much as possible to reduce humidity in the greenhouse.
(6) Timely harvesting. Before and after rain and snow, vegetables that can be marketed should be harvested in time. In particular, warm-loving fruit vegetables such as pepper, eggplant, tomato and cucumber should be harvested in time to reduce the plant burden, keep plants robust and improve plant stress resistance.
(7) Emergency response to chilling injury. For protected vegetable plants suffering chilling injury or slight frost damage due to damage to the greenhouse roof film, in addition to measures such as timely repairing the film, adding additional film covering and adding straw curtains to preserve heat and increase temperature, measures such as foliar spraying of 20-25°C warm water, 0.2% potassium dihydrogen phosphate solution and 0.5% urea solution can be taken to reduce plant damage. After frost damage occurs, the greenhouse should not be closed immediately to raise the temperature; the temperature inside the greenhouse should be allowed to rise slowly to avoid necrosis of frozen vegetable tissues caused by a sudden temperature rise. At the same time, stems, leaves and fruits that are severely frozen should be cut off in time.
(8) Step up repair of damaged facilities and replanting and supplemental planting. Vegetables in damaged facilities should be urgently harvested and transported in time to strive to reduce economic losses caused by snow disasters. For protected vegetables in early spring crops that have just been planted, if seedlings are missing or dead due to the disaster, fruit vegetables or leafy vegetables should be replanted or supplemented in time according to the situation.