In recent days, the temperature dropped sharply, and the cold injury of vegetables occurred frequently. Some inexperienced vegetable farmers often do not know how to prevent and suffer losses due to lack of understanding of such physiological diseases. The chilling injury of vegetables generally means that when the temperature has not reached the freezing point, the low temperature causes the physiological abnormality of the vegetables. The adaptability of various vegetables at low temperatures is different. In general, most leafy vegetables have strong tolerance to low temperature, such as Cruciferae, Compositae, and Umbelliferae vegetables. When they approach 0°C, they can also survive; while the cold resistance of melons and solanaceous vegetables is good. Relatively poor, such as cucumber, sweet pepper will die when near 0 °C. It is noteworthy that, whether it is leafy vegetables or fruit vegetables, when the environment does not reach a low temperature of 0°C, although it does not die, it encounters cold temperatures suddenly at low temperatures or at high temperatures for a long period of time. Physiological function can be abnormal, and the vegetative body or fruit exhibits various abnormal states. This is usually called cold injury. The common cold injury is divided into seven categories according to the symptoms: leaf spot, yellowing, wilting, flower topping, abnormal flower and fruit, early flowering or early bolting and falling flower and fruit falling. The methods for identification and prevention are described below. 1 Identification of cold damage 1.1 Leaf spot There are dead and small dead spots on the leaves. Lesions often start from the tips of the leaves or away from the veins, the color is light, or only the leaf part turns white. The appearance of such symptoms in open field vegetables is caused by cold currents, which are caused by cold killing of cells; but more of these symptoms are not necessarily related to air intrusion below 0°C, but due to sudden temperature temperature in the environment. Caused by changes; for example, when the greenhouse temperature suddenly rises, it will cause damage to the leaves or parts of the leaves. Many vegetable farmers call it "flashing." In addition, the chilling injury caused by the continuous low temperature in the protected areas may sometimes lead to the emergence of leaf blight, which is characterized by the dead edges of the leaves. This symptom often occurs in the late stage of the victimization, and the cold-damaged tissue is not recovered. 1.2 Huanghua The plants grew slowly, and the color of the leaves generally became lighter and yellowed. This chilling injury is often caused by the plants suffering from continuous low temperature, low illumination, weak photosynthesis, and overall lack of nutrition. Because of its symptoms are similar to nitrogen deficiency, it is often mistaken for a deficiency. 1.3 wilting Sudden low temperatures and slow temperatures can cause wilting. The wilting caused by the sudden low temperature mostly occurs when the shed temperature is high and the water is suddenly poured into cold water. This is due to the large amount of transpiration of the plants at high temperatures, the cold water causes the root activity of the plants to decline, and the water absorption in the roots is hindered. Seriously affected plants die due to severe imbalance in water. The wilting caused by the slow low temperature often occurs during continuous cloudy days. At this time, the temperature does not necessarily fall below 0°C, but due to prolonged low temperature and low illumination, the root absorption function is hindered. This cold injury tends to yellow the plants first and lasts for a long period of time. The plants are gradually wilting from top to bottom. 1.4 Flower topping This symptom is most common in cucumbers and other melons, that is, a large number of female flowers or small melons accumulate at the growing point of the plant, and the plant stops growing. The occurrence of flower topping is due to the fact that low temperature promotes the over-differentiation of flower buds, and the number of female flowers increases, but the plants lack sufficient nutrients for their growth and the vines cannot elongate, causing the female flowers to gather at the top of the plants. 1.5 Abnormal flowers and fruits This symptom is most likely to appear on tomatoes. The number of bracts in flowers begins to increase. The number of normal plant bracts is 6 and the number of malformed bracts is 7-10. The fruit produced is different from that of normal fruit except As the fruit color becomes lighter and smaller, the fruit cracks or becomes a long fruit, which resembles small fruit gathered together. Some people will ask when the appearance of abnormal fruit, often do not see direct contact with low temperature. This situation does exist. Studies have shown that malformed fruits begin to form during flower bud differentiation. For example, the first flower bud differentiation of tomato begins after the tomato seedlings are in two true leaves. If a temperature of 100° C. or less is encountered for a long time, the resulting ovary will be split into multiple fruits. It becomes a long one. This chilling injury occurs at the seedling stage and manifests itself during the fruit growth period. Often do not see the direct relationship with the low temperature. Sometimes improper use of auxin can also result in malformed fruit, but the resulting malformation only has a single bulge in the umbilicus, commonly known as "pap-like fruit." Therefore, it is inaccurate to classify malformed fruit as improper use of auxin. 1.6 Early flowers or morning twitches Most of these symptoms occur in cruciferous vegetables. When they encounter cold temperatures, these vegetables end prematurely in the vegetative stage and begin to grow into reproductive stages. Because of premature budding and flowering, they cannot obtain qualified products. For example, if broccoli and broccoli are encountered at a continuous low temperature, the plants grow buds when there are few leaves. Because the nutritional area of ​​the leaves is too small, the flower bulbs are not grown long and lose their commercial value. Another example is cabbage. Normal plants will form qualified leafballs during the harvest period, and plants that encounter cold damage will begin to form flower stems when they are not formed. Different species have different susceptibility to low temperatures. Generally strong winter varieties are less sensitive to low temperatures and can grow normally at lower temperatures. People usually arrange suitable sowing dates according to the characteristics of the varieties. However, due to the large differences in climate in different years, when it comes to late spring, it is often prone to early flowering and early bolting, causing losses to vegetable farmers. Some vegetable farmers attributed early flowering or early twitching to the problem of seed quality, which is inappropriate and should be scientifically analyzed. 1.7 Falling and falling fruit The occurrence of this condition is often due to the continuous low temperature caused by the lack of nutrition of the whole plant, so that the pollinated flower or the enlarged fruit can no longer develop, resulting in the separation and then fall off. In addition, chilling injury can also lead to bad seeding, seedling disease resistance decreased, and then induced a variety of diseases (flood disease, gray mold), not listed one by one. 2 Cold injury prevention and rescue The prevention of chilling injury should be carried out throughout the cultivation process. The main measures include the following aspects. 2.1 Improve the warmth of facilities and increase the temperature of the greenhouse This work should be done well when building a greenhouse. According to the latitude of each region, the suitable greenhouse height and the angle between the film and the ground are selected to optimize the photothermal effect of the solar greenhouse as much as possible. The cover of the greenhouse must be effective and impractical. If necessary, add a layer of straw curtains to the bottom corner of the sunny side or install a hot stove to increase the night temperature in the shed. In addition, the surface of greenhouse greenhouse film should be cleaned frequently to increase the light transmittance. 2.2 Grasp the susceptibility of breeds to temperature, choose appropriate sowing dates and planting dates based on medium and long-term weather forecast It is necessary to carefully read the instructions for the planting conditions of varieties, and it is better to plant the plants that are unfamiliar with winter sex after testing. According to the local climatic conditions, select the appropriate sowing date and planting period. When encountering special weather, take cold-proof measures as much as possible to protect the vegetables from cold damage. 2.3 Use temperature-changing management when raising seedlings to strengthen the ability to resist cold In the seedling stage of fruit and vegetables, temperature management shall be implemented according to the development requirements of the seedlings to cultivate strong seedlings. Generally, after sowing, the temperature should be increased. After emergence, the temperature should be lowered to avoid leggy; after the sub-seedling, the temperature should be raised again to promote the growth of new roots; the temperature should be reduced before planting to increase the cold resistance of the plants. In the cultivation of tomato seedlings, when the flower buds are differentiated (usually after two true leaves), the temperature at night is appropriately increased so that the night temperature is maintained at about 15° C. to prevent the occurrence of malformed fruit. 2.4 Doing Temperature, Moisture, and Nutrient Management in the Growing Period of Vegetables To control the temperature of the greenhouse, avoid excessive temperature in the greenhouse when it is sunny, especially when the temperature in the greenhouse is too high, release the air slowly to avoid sudden fluctuations in room temperature. In cloudy days, it is necessary to shorten the time for exposing the curtains, reduce the number of entrances and exits to the greenhouse, and maintain the temperature of the shed as much as possible. To avoid planting plants in vigorous growth with cold water when the temperature is high. When yellowing occurs on a continuous cloudy day, 0.5% to 1.0% sucrose + 0.1% to 0.3% potassium dihydrogen phosphate mixed solution can be used to supplement nutrition. When a continuous cloudy day causes plants to burp, they generally cannot be watered. If the weather starts to turn and the soil is dry, when watering is necessary, use a kettle to warm the water. Never use cold water to flood the area. To prevent the plants from being exposed to sunlight during a long period of sunny days, you can use the method of back squeezing (or squeezing them in intervals, and using insulation to return to the squat) to avoid sudden high temperatures. When the cucumber appears to have a flower topping, some of the juvenile melons may be properly removed to allow the shoots to elongate. In addition, spraying high-efficiency foliar fertilizers to strengthen the growth of vegetables will also help increase the cold resistance of the crops. 2.5 Before the emergence of low temperature smoke or night water This work applies to vegetables grown in the open. When the weather forecast will appear cold weather, timely release of smoke can use its drift, cover under the inversion layer, prevent large amounts of radiation at the ground temperature, in order to increase the ground temperature. You can also use the method of pouring night water to increase the temperature of the microclimate of the vegetable field. This measure is generally conducted in the middle of the second half of the night. When pouring, the amount of water must be controlled so as not to affect the ground temperature.