The factors affecting citrus cold injury can be summarized in two major categories: botanical factors and meteorological factors. The types, varieties (strains) of roots, rootstocks, tree age, shoot growth and cessation of shoots, the amount of fruit, the growth of the plants, and whether they are affected by pests are phytofactors. The most important meteorological factors are low temperature intensity and duration of low temperature, followed by the degree of dryness and humidity of soil and air, weather conditions before the low temperature (such as sunny, cloudy, cloudy or rainy days), wind speed, wind direction, and light intensity. And terrain, topography and so on.

Preventive measures against citrus freeze injury

1, choose cold-resistant varieties, cold-resistant rootstocks. In the broad-leaved oranges, the oranges, oranges, oranges, oranges, oranges, local oranges, oranges, and oranges are more resistant to cold. The pioneer oranges, brocades, and navel oranges in sweet oranges have stronger cold tolerance. Summer oranges, Xinhui oranges It is weaker. China's citrus rootstock is rich in resources, in addition to alfalfa, cold hardy Yichang orange, alfalfa and orange hybrids.

2. Choose good soil conditions and strengthen cultivation management

1 Soil is the place where citruses stand. The depth and fatness of the soil layer has a great influence on the cold resistance of citrus trees, with deep roots and leafy leaves, and increased cold resistance.

2 Improve citrus soil water conditions.

3 appropriate dense planting, moderate results. Proper close planting will not only benefit early, but also reduce the freezing damage in the citrus grove. The city is part of the northern margin of citrus cultivation, promoting soil transplanting, large seedling colonization, and dwarf close planting. This can lead to early results and benefit from the cyclical freeze, and it is also conducive to the increase of temperature in the citrus garden.

4 Control the autumn shoots in a timely manner to avoid unstimulated late autumn shoots and freezing. At the same time, when the soil temperature has not dropped, apply enough base fertilizer to promote the restoration of tree vigor and enhance the cold resistance.

5 Carefully prevent and treat diseases and insect pests that harm citrus leaves, branches and stems, so that the tree body has enough organs (leaves and robust stems) to make nutrition to resist cold invasion.

3, other kinds of cold measures

1 Build windbreaks and set up windbreaks.

2 earth and bandage the trunk. Due to the sinking of cold air, the temperature at the neck of the citrus is often the lowest. To prevent freezing of the roots and necks of citrus plants, especially saplings, soil and trunk dressing methods are commonly used to prevent freezing damage.

3 trunk white. The use of lime to coat white trunks has a certain effect on the prevention and treatment of main body frost damage. For example, adding appropriate amount of yellow mud and fresh cow dung in lime water has better antifreeze effect.

4 leaf spray steam insulation agent. The citrus canopy was sprayed with a steam-inhibiting and heat-insulating agent to form a layer of molecular film on the leaves of citrus, thereby inhibiting evaporation of leaf water and reducing frost damage.

5 Smoke cloud: before cold weather forecasts cool down or after heavy snowfall, on sunny, windless nights, weeds and weeds pile up in citrus groves as smoked stacks, burning in the evening to produce smoke, artificial clouds, It can suppress the backflow of radiation and prevent frost.

6 Antifreeze with water before freezing: Before the onset of the cold wave, irrigation in the citrus garden plays an important role in preventing freezing damage. Irrigation can increase the moisture content of the soil, and evaporation of water can prevent sudden drop in temperature.

4, citrus after treatment. The speed at which citrus trees recover after freezing depends on two factors: First, the degree of frost damage, and second, whether the recovery measures taken after freezing are timely and appropriate.

1 In case of heavy snow pressure on the crown, the snow on the canopy should be shaken off in time to avoid breaking the branches. Torn branches should be properly cut off leaves and reduce consumption.

2 When the ground is filled with water, especially after dry-frozen, the roots and trees need water, and they should be filled with water in time.

3 sloping soil warming. Immediately after thawing, loosen the soil under the canopy to keep the ground hot and increase the soil temperature. According to reports, six calories per hour can be released per square centimeter of surface area. In winter, the soil temperature is higher than the temperature, and the loose soil can maintain the soil heat, which is beneficial to the citrus root system.

4 fertilization protection recovery. After freezing, the function of the tree is significantly weakened. Fertilizer should be fertilized with water and be applied sparingly.

5 Trim and saw dry. After freezing, the branches are not as easy to identify in the short term as the leaves. After the branches are frozen, the catheters are not blocked, and the root-absorbed fertilizer water can still be consumed along the catheters as capillary water and gaseous water. If the branches are cut prematurely, miscutions will occur and the shears will be too late to make the tree waste water. Therefore, it must be cut (saw) in time to remove frozen branches. For larger wounds after cutting (saw), protective agents should be applied to reduce evaporation. Protective agent can be used yellow mud plus fresh cow dung plus 100ppm2.4-D; Vaseline 250 grams plus carbendazim 5 grams; butter 100 grams plus thiophanate 2 g.

6 dry white sunscreens. The frozen citrus trees, especially the branches and stems of the third and fourth frost damage, are painted with white paint to prevent sunburn and cause the tree trunk to dry.

7 control of pests and diseases. Pay attention to the prevention and control of aphids that harm the foliage to facilitate the growth of leaves and shoots.

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