Prevention and Control Methods and Technical Key Points for Frost Damage in Apple Trees
Frost damage has always been a common factor causing damage to fruit trees, and this is especially true for apple trees. Moreover, since apple trees are perennial plants, once frost damage occurs, its effects are long-lasting. The series of rot diseases caused by frost damage also gives fruit growers quite a headache. Below is a summary of the causes of frost damage in apple trees and the prevention and control measures.
1. Branches: Young twigs and shoot tips grow late, are not fully developed, and have insufficient tissue, making them susceptible to frost damage, drying up and dying. Externally, the branches show no major changes, but internally they turn dark brown, and in severe cases a black heart forms. Branches frostbitten in this way will not die immediately, but because the xylem vessels are blocked and cannot transport water freely, and the stored nutrients inside the branches are insufficient, sprouting is delayed, leaves are small or deformed, and growth is abnormal, forming branches that resemble little leaf disease, and they will slowly die.
2. Flower buds: In deep winter, temperatures are unstable. A brief warming reduces the cold resistance of flower buds, and a cold winter or fluctuating temperatures often lead to flower bud frost damage. Flower bud frost damage manifests as the inner scales turning brown, the stigma turning black and drying up, and in severe cases the entire flower bud drying up and dying.
3. Root crown: The root crown refers to the junction between the base of the trunk and the root system. The root crown enters dormancy later and breaks dormancy earlier. Being near the soil surface, when temperatures are low and cold resistance is weak, this is the main reason root crown frost damage occurs. Root crown frost damage manifests as the bark at the root crown turning black and dying; in mild cases it occurs locally, in severe cases it forms a black ring encircling the trunk, and in extremely severe cases it causes the entire tree to die.
4. Root system: The main causes of root system frost damage are that the roots beneath the soil surface are distributed too shallowly and heave upward, the topsoil is too loose or is sandy soil, and the winter is too cold or the cold winter lasts too long. Root system frost damage manifests as the outer bark turning dark brown, the bark separating from the xylem, and in severe cases completely detaching. When the soil temperature at the root base reaches -12°C to -16°C, apple roots begin to suffer frost damage.
Prevention and Control Measures
One: Wrap the trunk. Before severe frost arrives, use wheat straw or rice straw rope to wind around the main trunk and main branches, or make straw bundles to tie around the trunk, to prevent cold wind invasion and reduce frost damage. When bundling straw, the top of the straw should be tied tightly to the trunk with rope, with the bottom spread open; do not tie the whole bundle tightly, to prevent the trunk from freezing and instead suffering frost damage.
Two: Pruning. In late autumn or early winter, for deciduous fruit trees, especially 1-2 year old deciduous fruit trees, appropriate pruning or artificial defoliation can be carried out to reduce tree consumption, increase accumulation, and improve cold resistance and frost protection ability.
Three: Whitewash the trunk. In late autumn and early winter, whitewash the trunk as part of orchard cleaning. First, dissolve 5 kg of quicklime and 1 kg of salt separately in 20 kg of hot water, then mix and stir the two liquids, add 0.5 kg of lime sulfur stock solution and 0.1 kg of vegetable oil, and stir evenly to make the whitewash. First, it can kill overwintering pathogens and insect eggs on the trunk; second, it can enhance sunlight reflection, reduce the large fluctuations in day-night temperature difference, and avoid sunscald by day and freezing at night. When whitewashing, the trunk should be completely covered, all the way to the fork of the main and lateral branches.
Four: Winter irrigation for frost prevention. One and a half months after fruit harvest, when the soil is “frozen at night and thawing by day,” dig trenches between the fruit tree rows, then irrigate thoroughly along the trenches. The water volume should be such that it infiltrates completely before nightfall. This not only stores winter water for spring use, prevents spring drought, and promotes fruit tree growth and development, but also stores water and preserves heat, keeping the ground temperature relatively stable during cold waves, thereby reducing frost damage. After winter irrigation, it is best to cover with grass, or shallow hoe the soil surface to prevent water evaporation.
Five: For apple trees whose trunks are completely frostbitten but whose root systems are intact, the above-ground part can be sawed off at ground level. In March to April of the following year, re-graft using the cleft grafting or bark grafting method. If the trunk of a young tree is frostbitten, it can be cut back to the ground to resprout, keeping one vigorous shoot to rebuild the tree.
Six: For apple trees where healthy bark accounts for more than half of the trunk, bridge graft on the frostbitten side. For those severely damaged, they must be re-grafted.
Seven: For relatively mildly damaged apple trees, before bud break, spray 100-fold Duoxiao Miefuling to prevent rot disease. After bud break, scrape off the frost-killed bark and apply 843 Recovery Agent or Fuxing stock solution. During the apple tree growing season, use rot disease treatment agents to disinfect the branches and trunk, once every two weeks. 7-10 days after leaf expansion, spray once with Shengmingsu plus a small amount of urea, spraying 4-5 times consecutively. When pruning, besides cutting off frost-killed branches, wounds should be minimized as much as possible, following the principle of light pruning, leaving some branches unpruned, and heading back the extension branches to the point where vigorous shoots emerge.
Eight: If apple buds are damaged and both terminal buds and lateral buds are completely frostbitten, increase fertilizer application, provide water at the right time, and promote the sprouting of latent buds and accessory buds to rebuild branch groups.