What to Do About Freeze Damage in Fruit Trees? Management and Remedial Measures Explained

In winter, when temperatures drop below zero, poorly managed orchards are often susceptible to the effects of low temperatures, resulting in freeze damage to fruit trees. After fruit trees suffer freeze damage, root absorption and transport, leaf transpiration, photosynthesis, and plant growth are all disrupted. Therefore, management should focus on restoring the transport system as quickly as possible, healing wounds, promoting the sprouting of dormant buds, and returning to normal growth.

I. Symptoms of Fruit Tree Freeze Damage

1. Root freeze damage: Roots grow underground, so freeze damage is not easily detected, but the impact on the above-ground parts is very significant. It shows up as late or uneven sprouting in spring. In milder cases, although the tree can sprout and send out shoots, growth is slow; in severe cases, the new shoots gradually wilt and dry up. When roots are dug out, the outer cortex is found to have turned brown, with the cortex separating from the xylem or even falling off.

2. Root crown freeze damage: Root crown freeze damage is caused by drastic changes in the microclimate near the ground, where the absolute minimum temperature is lower than the air temperature and the temperature difference is large. It is especially likely to occur where water accumulates at the root zone and where the tree grows late into the season with excessive vegetative vigor. Sometimes the freeze damage occurs on one side of the root crown, forming a ring-shaped brown necrotic area.

3. Trunk and limb freeze damage: The main trunk splits, and branches and crotches are frozen. The cortex of frozen branches and crotches sinks or cracks, with browning and tissue necrosis inside. In severe cases, the cortex and cambium at the base of the tissue are completely killed by freezing, the affected branches wither, and the tree declines or dies.

4. Twig freeze damage: One-year-old branches of fruit trees are relatively cold-hardy. Late-growing, immature tender shoots are most susceptible to freeze damage and die back. Some branches look unchanged on the outside but leaf out late, with small or deformed leaves; when cut open, the xylem is seen to have turned brown.

5. Flower bud freeze damage: Flower bud freeze damage mostly occurs in early spring, because flower buds have broken dormancy, spring temperatures rise, and then frost occurs, causing freeze damage to the flower buds. In mild cases, sprouting is delayed, deformed, or stays at a certain stage of development for a long time; in spring the buds fail to swell, dry up, are small and thin, and drop easily. In some cases, the outside is not easy to detect, but when cut open, the bud pith is seen to have turned brown; in severe cases, the buds can die.

II. Preventive Measures Against Fruit Tree Freeze Damage

1. Choose a suitable orchard site: For newly developed orchards, choose a spot sheltered from the wind and facing the sun as much as possible, and avoid establishing an orchard in low-lying terrain or on a shady slope. Such sites cool down early in autumn, warm up slowly in spring, and accumulate cold air at night in winter, with lower accumulated temperatures.

2. Mulch the orchard with grass: Grass mulching can raise temperature, retain moisture, suppress weed growth, and increase soil organic matter content. Before mulching, deep-plow the soil, apply sufficient base fertilizer, water, and then cover with weeds. A thickness of about 20 cm, covered with a little soil on top, can greatly reduce the degree of freeze damage to fruit trees.

3. Strengthen fertilizer and water management: Apply fertilizer before bud break, mainly quick-acting nitrogen fertilizer and diluted human manure. Use 0.3%-0.4% urea plus 1%-2% superphosphate extract and 4% wood ash extract for foliar feeding, then spray again after 10 days with urea plus 0.3% monopotassium phosphate to promote new shoot growth and stimulate new root development. Where conditions allow, irrigate the orchard in time to increase soil moisture, regulate soil temperature, and prevent fruit trees from being frozen again. Practice has proven that rational fertilization and irrigation not only benefit fruit tree growth but also improve their drought resistance. Increasing organic fertilizer and phosphorus and potassium fertilizers helps the affinity of protoplasm for water and strengthens the plant's resistance to adverse environments, thereby helping fruit trees overwinter and improving yield. Controlling irrigation and appropriately reducing the water content of plant tissues can also enhance the cold resistance of fruit trees.

4. Timely and rational pruning of branches: Promptly remove frozen and dead leaves, and prune branches and trunks according to the extent of freeze damage. The pruning principle is to prune lightly and leave long shoots, keep more branches and leaves, leave fewer flower buds, reduce the load, promote new branch growth, and restore and expand the canopy as quickly as possible. In addition, newly planted young trees that have died from freezing should be replanted before bud break. Pruning can increase fruit tree yield, control pest and disease damage and spread, enhance nutrient accumulation in the plant, and help with cold resistance and overwintering. Remove overly dense branches to achieve ventilation and light penetration and to control vegetative growth.

5. Spray chemical agents: Some plant growth regulators can not only promote or inhibit fruit tree growth and improve yield and quality, but also enhance plant metabolism and regulate plant growth. They promote rooting and sprouting, increase fruit sugar content and coloring, and can enhance the cold and freeze resistance of fruit trees.

6. Timely prevention and control of pests and diseases: After freezing, fruit trees are weakened and have poor resistance, and in summer and autumn they are prone to gummosis and rot disease. Fruit tree wounds should be smeared with chemicals for disinfection, and fungicides such as carbendazim and metalaxyl mancozeb should be sprayed in time to prevent disease occurrence.

7. Protect flowers and fruits and maintain a reasonable load: For trees with few flowers due to frozen flower buds, take measures to protect flowers and fruits, such as strengthening fertilizer and water management and carrying out artificial pollination, to increase the fruit-setting rate; for trees with a large number of flowers and fruits, thin flowers and fruits in time after freezing and reasonably control the load; for trees with weak vigor, bear as few fruits as possible or none at all, and focus mainly on restoring tree vigor and increasing growth.

8. Other measures: Before winter begins, whitewash the trunks with lime slurry, which helps control pests and diseases and improves cold and freeze resistance. For young trees, methods such as wrapping the trunk with grass or building a semicircular soil ridge on the north side can also be used for protection.