Prevention and Control of Frost injury of Apple trees

Freezing injury has always been a common cause of damage to fruit trees, especially apple trees, and apple trees are perennials. Once freezing injury occurs, the impact is lasting. A series of rot diseases caused by freezing injury are also a headache for fruit growers. Below, the causes and control measures of freezing injury of apple trees will be summarized.

1. Branches: shoots and shoots grow late, immature, tissue is not full, easy to suffer frost injury and dry up and die. From the outside, there is no big change in the branches, but the interior will become dark brown, causing a black heart in serious cases. In this way, the frostbitten branches will not die immediately, but because the xylem ducts are blocked and cannot smooth water, the branches lack stored nutrients, sprout late, the leaves are thin or abnormal, grow abnormally, and form branches similar to leaflet disease. will slowly die.

2. Flower buds: the temperature is unstable in deep winter, and the cold resistance of flower buds decreases due to short-term warming, and cold winter or sudden cold and hot temperatures often lead to frost injury of flower buds. The frost injury of flower buds showed that the internal scales turned brown, the stigma blackened and withered, and in severe cases, the whole flower bud withered and died.

3. Root neck: the root neck refers to the junction of the trunk base and the root system, the root neck enters dormancy later, and the dormancy is released earlier. Near the surface, when the temperature is low and the cold resistance is weak, it is the main cause of root neck frost injury. The frost injury of the root neck showed that the cortex of the root neck blackened and died, slightly occurred locally, and formed a black ring around the stem, which caused the death of the whole tree when it was too serious.

4. Root system: the main reason of root freezing injury is that the distribution of root system under the surface is too much and floating, the topsoil is too loose or sandy soil, and the winter is too cold or the cold winter lasts for a long time. The freezing injury of root system showed that the outer cortex became dark brown, the cortex was separated from xylem, and in serious cases, it would be completely detached. When the temperature of the root soil reaches-12 ℃ to-16 ℃, the apple roots begin to freeze.

Prevention and cure measures

One: bandage the tree trunk. Before the big frost injury comes, wrap the trunk, the main branch or make the straw with wheat straw and straw rope to prevent the cold wind and reduce the freezing injury. When bundling grass, the top of the grass should be tied to the tree trunk with a rope, spread out below, do not tie the whole grass tightly, in case the tree trunk freezes and suffers frost damage.

Second, pruning. In late autumn or early winter, deciduous fruit trees, especially 1-2-year-old deciduous fruit trees, can be properly pruned or artificially deciduous, so as to reduce tree consumption, increase accumulation and improve the ability of preventing cold and freezing.

Third, paint white tree trunks. At the end of autumn and the beginning of winter, the trunk was painted white in combination with Qingyuan. First, 5 kilograms of quicklime and 1 kilogram of salt are melted in hot water 20 kilograms respectively, then the two liquids are mixed and stirred, and then 0.5 kilograms of stone-sulfur mixture and 0.1 kilograms of vegetable oil are mixed evenly to make a whitening agent. First, it can kill the overwintering germs and eggs of the tree trunk; second, it can enhance the ability of sunlight reflection, reduce the great change of temperature difference between day and night, and avoid sunburn and night freezing. When drying, coat all the tree trunks up to the branches of the main side branches.

Fourth, winter irrigation to prevent freezing. One and a half months later, when the soil is "frozen at night", dig ditches between the rows of fruit trees, and then pour water through the ditches. The amount of water should be finished before nightfall. It can not only achieve the use of winter water in spring, prevent spring drought, promote the growth and development of fruit trees, but also store water and heat preservation, so as to keep the ground temperature relatively stable during the cold wave, so as to reduce frost damage. After winter irrigation, it is best to cover grass or hoe the surface to prevent water evaporation.

Fifth, for apple trees with frozen trunks and complete roots, the aboveground parts can be cut off on the ground. From March to April of the following year, split grafting or subcutaneous grafting was used again. If the trunk of the young tree is frozen, it can be reproduced after stubble, leaving a strong sprouting branch and re-cultivating the tree.

For example, apple trees with more than half of the trunk bark are bridged on the frozen side. If the victim is serious, it must be regrafted.

7. The lighter damaged apple trees should be sprayed with 100-fold multiple rotting agent to prevent rot before sprouting. After sprouting, scrape off the frozen bark and apply 843 rehabilitation agent or putrefaction solution. Disinfect the branches with drugs to treat rot during the growing period of apple trees, once every two weeks. Spraying vitamine with a small amount of urea 7-10 days after leaf spreading, spraying 4 times in a row. In pruning, in addition to removing the frozen dead branches, the wound should be reduced as far as possible, with light cutting as the principle, slowly release part of the branches, retract and extend the branches to the part of the strong branches.

8. Apple buds are damaged, and terminal buds and lateral buds are all frozen. It is necessary to increase the amount of fertilizer application, timely water supply, promote hidden buds and secondary buds germination, and re-cultivate branches.