How Kiwifruit Can Safely Overwinter in Winter: Preventing Freeze Damage and Post-Freeze Remediation

Winter is an important period for kiwifruit to restore tree vigor and conserve strength. Winter management of kiwifruit must be effectively strengthened to ensure that kiwifruit can overwinter safely and to lay a good foundation for a bountiful harvest the following year. So how can a kiwifruit orchard safely overwinter in winter? How can freeze damage be prevented? How should kiwifruit trees be remediated after freeze injury?

I. Symptoms of Freeze Damage in Kiwifruit

Areas prone to freeze damage are mainly distributed in river beach land, plots with poor air circulation, low-lying areas and the Qinling river valley zone; freeze damage of varying degrees also occurs in other areas.

1. Generally, 1-2 year old newly grafted young trees are most susceptible to freeze damage; newly bearing Xuxiang and other kiwifruit varieties with excessively vigorous growth suffer relatively severe damage, while seedling trees and orchards in full fruiting stage suffer lighter freeze damage.

2. The frozen parts are mostly the kiwifruit trunk, mainly within 50 cm above the root crown. The frozen parts show longitudinal cracking of the cortex, sap exudation from the frozen areas, and an apparently intact epidermis that, when scraped open, reveals browning of the inner cortex. Trees suffering light freeze damage are injured, while severe cases can cause the tree to freeze to death, seriously affecting kiwifruit profitability.

II. Prevention Measures for Freeze Damage in Winter Orchards

1. Apply an appropriate amount of warming fertilizers to improve the cold resistance of crop plants.

In winter, an appropriate amount of warming fertilizers such as phosphorus, potassium and boron fertilizers, plant ash, burnt soil or farmyard manure, and decomposed pig and chicken pen manure can be applied to increase soil temperature, improve plant cold resistance, and be combined with spraying 600 times dilution Wofengsu foliar fertilizer. Drenching with solid Diliwang soil conditioner improves the soil, promotes robust plant growth, and enhances the crops' own cold resistance.

2. Protect crop plants in the plantation well to improve winter cold resistance

(1) Covering. Before severe cold, short kiwifruit can be protected from cold by building a straw shed frame over the whole plant, while tall kiwifruit can be covered with mesh made from discarded plastic bags, or covered with cold-protection materials such as straw curtains to raise the temperature.

(2) Trunk wrapping. Before severe cold arrives, wrapping the main trunk and main branches of kiwifruit trees with straw or plastic film can effectively prevent freeze damage.

(3) Irrigation before freezing: if autumn and winter drought is severe, one thorough irrigation can be given before severe cold, and where conditions permit, another irrigation before the arrival of cold air gives better results. Irrigation after freezing: after crops are frozen, leaves lose a large amount of water, so irrigation must be done immediately to reduce excessive water loss from crop plants and prevent them from dying.

3. Use smoking to disperse cold currents and frost. Before low temperatures arrive or on the night of frost, pile weeds, rice husks, sawdust, dry branches and leaves or other smoke-producing materials in the crop field for smoking, with 3—5 piles per mu, lit at around 10 p.m., and a smoking duration of 6—10 hours is suitable.

4. Strengthen field management and carry out pest and disease control well. Timely intertillage and hilling, adding microbial agents (Diliwang), which can degrade into the best organic fertilizer for crops, making the soil loose and breathable; do a good job of clearing ditches and draining waterlogging to facilitate root growth, enhance tree vigor, and improve the tree's disease resistance. Timely remove frozen dead remains as well as yellow and withered leaves, and effectively carry out winter control of various pests and diseases so that crops grow robustly.

5. Disinfection with fungicides. For management after fruit harvest, it is generally necessary to spray the leaves once with a fungicide; Liangguoan at 300 times dilution is recommended for spraying. Replenish nutrients, repair wounds, and promote healing. For trunks with wounds, peeling or cankers, use Kuifuling to brush the trunk, expanding the range as much as possible and brushing a longer section, or spray at high concentration, while combining with Qingkulike and Wofengsu for root drenching for better results.

6. Whitewashing for freeze protection. After leaf fall, whitewash the tree bodies of orchards already on trellises, mainly coating the main trunk and branch and vine areas. Whitewash formula: 10 parts water + 2 parts quicklime + 1 part lime sulfur mixture + 0.5 part salt + a small amount of animal and vegetable oil.

III. Remedial Measures After Freeze Damage Occurs

1. Strengthen pest and disease control. After freeze damage occurs, tree wounds increase and resistance decreases, making disease occurrence most likely to worsen. Kiwifruit pest and disease control, especially of bacterial canker, should be strengthened; agents such as Fulanke, Shenaning, thiodiazole-copper and copper hydroxide can be used alternately, spraying once after pruning work is completed, and spraying 2-3 times in the early disease stage (mid-February—early to mid-March).

2. If the bark has freeze cracks, before budding in spring, breathable materials can be used to wrap the wounds to prevent water evaporation and contamination by miscellaneous fungi, aiding wound healing.

3. After frozen fruit trees bud, pay attention to selecting and cultivating root suckers; for plants frozen and killed, the suckers sprouting from the base can be used, and after lignification, a new trunk can be cultivated by cleft grafting.

4. For individual fruit trees with severe freeze damage, where the main trunk cortex is severely cracked and the cortex has turned brown and necrotic, preventing nutrients from being transported to the root system, bridge grafting should be carried out promptly to ensure the supply of water and nutrients to the upper and lower parts of the tree.