Remedial measures for Frost injury of Citrus trees damaged by extremely strong Frost and Snow

Recently, most parts of our country have suffered serious frost injury. in order to reduce the loss and restore the tree potential ahead of time, the following measures to restore citrus frost injury are provided for fruit growers' reference.

Citrus frost injury

1. Pruning according to the degree of citrus freezing injury:

(1) lightly frozen trees: the frozen and scorched leaves will continue to consume water and expand the frozen surface, so they should be knocked down as soon as possible to prevent the branches from dying. Distinguish between frozen branches, light cutting and leaving more leaves, annual branches without leaves can be as short as two years old, leafy branches are not pruned temporarily, and green branches and leaves are retained as far as possible.

(2) Frozen trees: if the boundary between life and death of frozen branches is obvious, they shall be renewed and pruned at the sprouting place. The degree of pruning varies from tree to tree, pruning is carried out in different times, first light and then heavy, determine the sawing position, from the perspective of the whole tree shaping, in order to cultivate a new high-yield crown.

(3) heavy frozen trees: if the main branches are frozen to grade 3-5, they need to be explicitly renewed; if frozen to grade 1-2, they need to be cut off and renewed.

(4) Frozen dead trees: general grafted trees with Fructus Aurantii rootstock, the roots are not easy to die, and their sprouting roots and tillers should be strengthened in time and 3 branches should be retained for grafting.

2. Fertilization:

After the citrus is frozen, it will lead to a large number of fallen leaves, especially the heavily frozen trees. after pruning, there are few healthy leaves left, the aboveground parts do not have enough nutrients to supply the underground parts, and the root absorptive capacity is weak. When the temperature rises in spring, the tree sprouts a large number of shoots, and the nutrient supply will be out of balance, which is disadvantageous to the recovery of the tree potential. According to the physiological changes of frozen trees, we should master the principles of early application, diligent application and thin application in fertilization. From February to March, mainly available nitrogen fertilizer, applied not less than 3 times, 10-year-old citrus trees, each time applied not less than 100 grams of urea, and mixed with clear fecal water 1015kg, trench around the tree plate. The leaves of frozen trees are not deciduous, due to the decrease of chlorophyll caused by freezing injury, and the poor photosynthesis caused by small and thin leaves. Foliar fertilization can improve leaf quality and photosynthetic function. Foliar fertilizer spraying can be carried out many times, with an interval of 15 to 20 days, generally spraying 0.1% urea and 0.3% 0.5% potassium dihydrogen phosphate. If there is element deficiency in frozen trees, the missing elements combined with foliar fertilization can be supplemented according to the judgment of leaf surface.

3. Strengthen tree protection, disease and pest control:

(1) Light frozen trees: after the occurrence of frost injury, spray 1Vera 100 times Bordeaux liquid or 800 × 1000 times Topu body liquid, or Baume 0.3 degree stone sulfur mixture in time to prevent leaves and shoots from getting sick.

(2) treatment of medium and heavy frozen tree shears (saws) and frozen wounds: the shears (saws) should be cut into smooth slopes, and then disinfected with 75% alcohol or 0.1% potassium permanganate, and after disinfection, the wound should be coated with protective agent. The protective agent can be prepared with butter or Vaseline with 2% topiramate.

(3) Prevention and treatment of resin disease and sunburn:

After the citrus is frozen, it is easy to induce resin disease, and the wound is an important epidemic condition, so after freezing, in addition to paying attention to cut (saw) mouth, wound disinfection, protection and treatment, it is necessary to scrape the speckles on the deep branches in time, and then use 50% carbendazim 100 liquid, or 50% carbendazim 200x solution, or 1:1:10 Bordeaux pulp, or 1:4 edible lye, or tarmac containing 2% carbendazim. Heavy frozen trees are prone to sunburn and cracking in summer and autumn due to large amount of pruning, few leaves and bare trunks. In order to prevent sunburn, the branches were brushed with whitening agent for 2 or 3 times from June to August. 5 parts of lime, 0.5 parts of sulfur powder, 0.1 parts of salt, 0.1 parts of tung oil and 20 parts of water were used for whitening agent.

In addition, after citrus is frozen and pruned, a large number of branches and young leaves will germinate. Attention should be paid to the prevention and control of aphids, whiteflies, mites, pink butterflies, latent leaves, soot, anthracnose, scab and other diseases and insect pests that harm young shoots and leaves, so as to avoid getting out of control.