Occurrence and Control of Frozen Damage to Apple Trees
As winter approaches, there will be different degrees of frost damage of apple trees every year in apple growing areas, causing some losses in production. The freezing injury of apple trees varies with the time and area of ​​occurrence, and the symptoms of freezing injury are also different. Common types of freezing injury and its prevention methods are as follows: (I) Types of Freezing Damage The early winter-type freezing injury in late autumn falls from late November to early December. Before the apple is plucked into the fallen leaves, the tree has not yet completely hibernated, the weather is unusually warm, and the average daily temperature reaches around 15°C, which induces the dormant late main branch base and trunk. The physiology and activity of the formation layer and bark of the dynasty are not active and can not be hibernated in time. The ability to resist cold is low. Suddenly there is strong wind cooling or cold current. The temperature drops to -3°C to -5°C. After a few hours, these parts are The formation and deep bark are frozen and become light brown. In the second spring, during the germination period, the large branches or trees above the frozen part could not germinate. After the normal fruit trees were dropped, the frozen or whole trees could not germinate, and the formation and deep bark of the frozen parts changed. Become dark brown and eventually die. However, the shallow bark remains white and green. About 1 month after flowering, the frozen part of the bark sunken and shrank. Large or heavily frozen bark cracks and warps, and the subcutaneous xylem is dark brown. Frosted bark is prone to rot near frozen bark. In the winter, when the fruit trees enter the dormant period, the cold and frost-damaging winter fruit trees have strong frost resistance. However, in winter when there is an abnormally low temperature, the relatively thin bark of the bark often suffers from low-temperature freezing injury, and the light part of the pith tree turns brown and dies. The xylem and bark become brown and die. At the same time flower buds are also subject to freezing and browning, and sometimes winter temperatures fall below -25, and large branch bark is also frostbite, turning brown and dead. After the spring season began to defrost, the temperature rose rapidly, and the air was dry. There was a gale, the water evaporation from the shoots was large, and the soil under the trees had high humidity or deep roots. The soil at the root level was still frozen. , can not fully absorb water supply to the upper part of the ground to start moving branches, resulting in thin skin, thin bark of the tree severe water loss and shrinkage, become purple brown or dark purple, phloem and xylem whitish, dry, late dry death, can not be issued New foliage. Late frost-type frost damage of apple blossom buds to the frostbite during the flowering period, the initial performance of the general style, stigma, anthers from green to brown, followed by wilting, dry. The light, male and pistil were frozen and the flowers could still be developed, but the fruit could not be set. When the cold injury was severe, the petals were water-stained and withered off. Young fruit in the double-ring type freeze-thaw apple young fruit is generally about 7-10 days after flowering. When it encounters low temperature or night frost below 3°C, a ring-shaped contracture occurs above the sepal and soon forms a crescent-type depression spot, and continues to develop into a The purple-red spot around the top of the fruit has browned, necrotic, and corked pulp in its subcutaneous layer. As the fruit grows, the victim suffers from a large amount of shedding. From the falling fruit to the ripening stage, there are still rings or discontinuous dark brown sunken scars around the ankle. Such low-temperature freezing damage generally occurs lightly on the slope, and occurs under the slope. The occurrence of saplings in the depression is heavy, and the occurrence of large trees in flat land is light. The incidence of Qin Guan and Fuji varieties is heavy, and the incidence of Golden Crown varieties is lighter. (B) Control methods 1. Late-autumn and early-winter orchards that are prone to frost damage should be controlled after the adoption of nitrogen fertilizers in July. Phosphorus and potassium fertilizers should be sprayed on the trees to control growth and promote the ripening of branches and the return of nutrients. In orchards with irrigation conditions, they must fill the frozen water in time. In the late autumn, the main trunk and the lower middle of the big branch are painted white. Before the saplings enter the winter, they must cultivate the earth. Roots and stems that are susceptible to freezing can be picked up in the late autumn when the rhizomes are soiled. 2. For the orchards that occur frequently in the spring and autumn night frosts, water should be poured before the spring fruit trees are germinated, and then germinated before flowering. 2-3 times more water. This can delay the phenological period of fruit trees by 2-3 days to reduce the degree of freezing. According to the weather forecast, it is possible to increase the orchard's heat capacity by filling the water before the buds are sprouted. This will have a significant antifreeze effect on the short-term temperature drop of around -3°C. 3, before the spring flower buds sprouting, combined with the prevention and treatment of strut diseases, spraying 10% of Kang Kang Po film 80-100 times liquid, to prevent freezing damage of flower buds above -3 °C, have a certain effect, can reduce the freezing rate of flower buds About 30%. 4. To prevent night frost and frost damage during flowering, according to the weather forecast, put a pile of weeds every 20-30 meters in the orchard. When the temperature drops below 0°C, start the ignition and press the soil to smoke. The tree body can also be sprayed with water to increase the heat capacity to reduce freezing damage.
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