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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, drier air, and lower temperatures. These conditions can easily lead to frost damage in fruit trees, especially during early winter and early spring when the weather is dry, windy, and characterized by large temperature fluctuations between day and night. Such conditions can cause fruit stripping and freezing injury, which significantly affects fruit tree production. To address this issue, we will take special apples and pears as examples to analyze the causes of frost damage and introduce effective preventive measures.
**I. Causes of Winter Frost Damage in Apples and Pears**
1. **Unusual Climate Changes**: Sudden drops in temperature, especially in early autumn, or rapid changes in day and night temperatures can cause significant frost damage to fruit trees. After the onset of spring, as temperatures gradually rise, apple and pear trees begin to come out of dormancy. Their cold resistance weakens, making them highly susceptible to low temperatures. If the temperature falls below -2°C for more than 30 minutes, freezing damage can occur.
2. **Low Cold Resistance in Certain Varieties**: Some apple varieties, such as India, Green Banana, and Fuji, and certain pear varieties like 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 frost. Similarly, trees that grow too vigorously and fail to stop growth in late autumn may have underdeveloped protective tissues, increasing their susceptibility to freezing injury.
4. **Mechanical Damage and Pest Infestations**: Trees that have suffered mechanical damage or severe pest infestations are less able to withstand cold stress, making them more likely to experience winter casualties.
**II. Protective Measures**
1. **Planting Shelterbelts**: Establishing shelterbelts around orchards can increase the temperature within the orchard by 2–5°C, reducing the risk of frost damage. These belts, typically made of shrubs and trees, provide excellent protection against cold winds.
2. **Selecting Cold-Resistant Varieties**: Choosing varieties known for strong cold resistance, such as Marshals, Guoguang, and Sweet Yellow Kuwait for apples, and Snow Pear for pears, can significantly reduce the risk of frost damage.
3. **Pre-Irrigation**: Watering the soil before a cold spell increases its heat capacity and thermal conductivity, helping to regulate soil temperature. This can help protect fruit trees from sudden temperature drops.
4. **Strengthening Tree Vigor**: For weak trees, it's important to provide adequate nutrients and water early in the growing season. In late summer, reducing nitrogen fertilizer and applying phosphorus, potassium, and organic manure helps control excessive growth and promotes maturity.
5. **Pest and Disease Control**: Managing pests and diseases effectively is crucial. Treating wounds caused by mechanical damage or pruning with wax or bandages can prevent further damage and maintain the tree’s health.
6. **Frost Smoke Burning**: When frost is expected, burning straw, weeds, or branches in the orchard can create smoke that reduces heat loss and raises the temperature slightly, offering some protection.
7. **Tree Wrapping**: Covering the main branches and trunk with straw or plastic film before winter helps insulate the tree and retain moisture, improving its ability to survive the cold.
8. **Antifreeze Sprays**: Applying antifreeze agents, such as potassium dihydrogen phosphate mixed with white sugar, before a cold event can enhance the tree’s cold resistance. Painting the trunk with a lime-based whitewash also provides additional protection.
9. **Mulching**: Covering the ground with a layer of weeds, leaves, or manure (about 10–15 cm thick) can raise the ground temperature by 3–5°C, offering an extra layer of frost protection.
**III. Post-Frost Care**
After a frost event, it's important to strengthen soil management and apply nitrogen fertilizer to help the trees recover. For damaged bark, nails should be used to keep cells moist, and dead tissue should be removed to allow nutrient flow. In cases of severe damage, more nitrogen fertilizer should be applied to promote the formation of new xylem and cortex. Pruning should be avoided in spring; instead, focus on managing flower and fruit load to restore tree vigor. Retain leaf area and avoid excessive pruning to support recovery.
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