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The causes of casualties of fruit trees in winter and protective measures
The northern region experiences more sunny days during winter and spring, with less rainfall, dry air, and lower temperatures. These conditions can easily lead to frost damage in fruit trees, especially during early winter and early spring when the climate is dry, windy, and marked by large temperature fluctuations between day and night. Such conditions increase the risk of fruit stripping and freezing injury, which can severely impact fruit tree production. To better understand and address these challenges, this article focuses on apples and pears, analyzing the causes of winter damage and introducing effective preventive measures.
**I. Causes of Winter Damage in Apples and Pears**
1. **Abnormal Climate Changes**: Sudden drops in temperature during early autumn or rapid temperature swings between day and night can cause frost damage. After spring begins, as temperatures rise, apple and pear trees gradually exit dormancy, and their cold resistance weakens. If a temperature drops below -2°C for more than 30 minutes, freezing damage may occur.
2. **Low Cold Resistance in Certain Varieties**: Some apple varieties like India, Green Banana, and Fuji, as well as certain pear varieties such as Dangshan Pear, have poor cold resistance and are more prone to frost damage.
3. **Weak Tree Vigor or Poor Growth**: Trees that are weak or not fully developed have lower cold resistance and are more vulnerable to freezing. Similarly, overly vigorous trees that continue growing late into autumn may not develop strong protective tissues, increasing the risk of frost damage.
4. **Mechanical or Pest Damage**: Trees that suffer from mechanical injuries or severe pest infestations also have weakened cold resistance, making them more susceptible to winter casualties.
**II. Protective Measures**
1. **Establishing Orchard Windbreaks**: Planting windbreaks using dense shrubs and trees can raise the temperature within the orchard by 2–5°C, effectively reducing the likelihood of frost damage.
2. **Selecting Cold-Resistant Varieties**: Choosing apple varieties like Guoguang and Sweet Yellow Kuwait, and pear varieties such as Snow Pear, can significantly improve the chances of survival during cold periods.
3. **Pre-Frost Watering**: Watering the soil before a cold spell increases its heat capacity and thermal conductivity, helping to moderate soil temperature and reduce frost damage.
4. **Strengthening Tree Vigor**: For weak trees, applying more nitrogen fertilizer and improving soil conditions can promote healthy growth. In late summer, reducing irrigation and nitrogen fertilizer while increasing phosphorus and potassium helps control excessive growth and promotes maturation.
5. **Pest and Disease Control**: Managing pests and diseases is crucial. Treating wounds caused by pruning or pests with wax or bandages helps prevent water loss and further damage.
6. **Frost Smoke**: When frost is expected, burning straw, weeds, or branches in the orchard creates smoke that reduces heat loss and raises the temperature slightly.
7. **Tree Wrapping**: Covering trunks and branches with straw or plastic film before winter protects trees from cold. This method also helps trap insects that overwinter in the material.
8. **Antifreeze Sprays**: Applying antifreeze agents, such as potassium dihydrogen phosphate or white sugar solutions, before low temperatures can enhance cold resistance. Painting tree trunks with a whitening agent made of lime, salt, and sulfur also provides protection.
9. **Mulching**: Covering the ground with weeds, leaves, or manure up to 10–15 cm thick can raise the soil temperature by 3–5°C, offering additional frost protection.
**III. Post-Frost Care**
After a frost event, it's important to strengthen soil management and apply nitrogen fertilizer. For damaged bark, nails should be placed to maintain cell moisture, and dead tissue should be removed to keep nutrient flow open. In cases of severe damage, more nitrogen fertilizer should be used to stimulate new growth. Pruning should be avoided in spring; instead, focus on maintaining leaf area and reducing the load on the tree to help it recover.