Why should fruit tree winter freeze protection not be overlooked?
In the past three years, our province has experienced warm winters for three consecutive years, with average winter temperatures higher than normal. Since the start of winter this year, temperatures have continued to be on the high side, and it should be another warm winter. A warm winter causes fruit trees to stop growing late and reduces their cold resistance. If a sudden sharp drop in temperature occurs, freeze damage is extremely likely. Fruit growers should not neglect freeze protection management for fruit trees just because the winter is warm, causing losses to fruit production. Orchards in the following situations in particular deserve even more attention.
1. Orchards with newly planted young trees. Vigorous mature fruit trees develop fully and have strong cold resistance, so freeze damage is generally mild. But newly planted young trees, because of their habit of vigorous growth, stop growing late, have insufficiently developed root systems, and have poor shoot development, so their cold resistance is poor. They are prone to freeze damage when temperatures drop, and after freeze damage occurs, it affects shoot sprouting in spring and readily causes shoot dieback, leading to tree death.
2. Orchards planted with tree species or varieties with poor cold resistance. Different tree species and varieties have different resistance to freeze damage. For tree species and varieties prone to freeze damage, freeze protection work must be done even better. For example, pear, jujube and other tree species have relatively strong cold resistance, so the possibility of freeze damage is relatively small. But apple, peach, apricot, grape, walnut, cherry and other tree species have relatively poor cold resistance and are prone to freeze damage, especially some varieties with poor cold resistance among these species, for which freeze protection work must be done even better. Examples include Red Fuji among apples, 21st Century and Zhonghua Shoutao among peaches, and most grape varieties. Although pear trees have somewhat stronger low-temperature resistance, some varieties are also prone to freeze damage, such as Xuehua pear, Huangjin pear, Huangguan pear and Yuluxiang pear, whose flower buds are easily damaged by freezing, developing stiff buds and failing to bloom normally in spring, affecting fruit set and causing reduced yield, which should be given attention in production.
3. Orchards with low management levels and poor site conditions. Orchards sheltered from the wind and facing the sun suffer relatively mild freeze damage, while shaded orchards, low-lying orchards and sandy orchards suffer relatively severe freeze damage. In orchards with good management, fruit load is reasonable, organic fertilizer is valued, chemical fertilizer is applied rationally, the trees are vigorous, stored nutrients are sufficient, branches and buds are well developed, cold resistance is strong, and freeze damage is not likely to occur; conversely, in orchards with excessive fruiting and excessive nitrogen fertilizer application, new shoots tend to grow vigorously, stop growing late, shoots develop poorly, the trees are falsely vigorous, and freeze damage is likely to occur.
In view of the above situations, the following work should be done well to prevent fruit tree freeze damage.
1. Do a good job of summer management of fruit trees. First, keep the load reasonable to prevent insufficient tree nutrition. Second, pay attention to using more organic fertilizer and less chemical fertilizer. At the same time, match nitrogen, phosphorus and potassium reasonably, with an annual application ratio of about 1:0.5:1, and be sure to control the amount of nitrogen fertilizer in the later growth stage, so that the trees are vigorous, stop growing promptly after the start of winter, and have well-developed shoots, improving cold resistance.
2. Spray phosphorus and potassium fertilizers. In October, the trees are still in the growth period, and phosphorus and potassium fertilizers can be sprayed on fruit trees; if conditions permit, trace elements can be added to promote full development of shoots and flower buds and improve the freeze resistance of the trees and flower buds. For example, a 0.3 percent potassium dihydrogen phosphate solution can be sprayed. Spray once every 5 to 7 days, for two consecutive sprays.
3. Irrigate sufficiently with freezing water. Before the start of winter, winter irrigation should be carried out in the orchard. On one hand, it enhances the freeze resistance of the trees; on the other hand, it can use the high specific heat of water to enhance the orchard's buffering capacity against temperature changes. At the same time, it can prevent spring drought the following year, which causes shoot dieback.
4. Whitewash tree trunks. For tree species and varieties prone to freeze damage or orchards with poor management, tree trunks should be whitewashed, mainly the main trunk, main branches and large branches, which is very effective in preventing freeze damage.
5. Orchard mulching. In winter, cover the tree discs in the orchard with crop straw, green manure, etc., generally 10 to 20 cm deep. Plastic film mulching can also be used. This can effectively raise ground temperature and prevent fruit tree freeze damage. At the same time, prevent straw from catching fire.
6. Key protection. For tree species and varieties with obviously insufficient cold resistance, key protection should be carried out. For example, fruit growers planting Zhonghua Shoutao should, before the start of winter, wrap the aboveground trunk and main trunk about 1 m high with corn straw for freeze protection, then remove it in spring.
7. Reasonable pruning. Do not prune too heavily; keep a suitable amount of branches in the tree, which is beneficial for freeze resistance. Larger pruning and saw cuts should be painted promptly to prevent excessive water loss and weakened cold resistance. If the amount of flowers retained is relatively large, flower thinning pruning can be done before flowering in the following spring.
8. Bark scraping should not be done too early. Bark scraping can remove most pests and diseases that overwinter in bark crevices, reduce the occurrence of pests and diseases the following year, and at the same time promote tree metabolism, which is beneficial to the normal development of fruit trees. Tree species such as apple and pear often use this technique. But scraping bark too early removes the outer old tissues with strong freeze resistance, exposing the tender inner tissues, which makes freeze damage likely, causing the tree to weaken and affecting normal growth and fruiting. Therefore, bark scraping work should be appropriately postponed, and the time can be set from late February to early March of the following year. Also, be careful not to scrape too heavily; generally, it is enough to scrape until the bark shows white.
9. When necessary, carry out orchard smoke fumigation and clear snow. For some varieties with poor cold resistance, when a major cold wave arrives, carry out orchard smoke fumigation to raise the microclimate temperature of the orchard. After heavy snow, clear the snow from the trees before it melts, to prevent the temperature drop during snowmelt from causing freeze damage to fruit trees.