How to prevent fruit russeting in Huangjin pear? Causes and measures

Huangjin pear was introduced to our city in 2000. Through top-grafting and variety replacement, it has now expanded to 2567 hectares, and began bearing fruit in 2001. However, in production it was found that the fruit surface of Huangjin pear is prone to forming fruit russeting, with the rate of good fruit at 30%-50%, seriously affecting the economic benefits of fruit growers. For this reason, we conducted investigation and analysis, identified the causes and proposed corresponding countermeasures.

1. Causes

Internal factors: The occurrence of Huangjin pear fruit russeting is closely related to its peel structure. The epidermal cells of Huangjin pear fruit not only have thickened outer walls but also secrete cutin outward, causing the cell walls to become cutinized and forming a cuticle layer on the outside. However, the cuticle layer structure of Huangjin pear is not uniformly arranged or densely layered, but instead loosely attached to the fruit epidermis. This peel characteristic of Huangjin pear makes it susceptible to damage. Once affected by adverse external environmental conditions, the cuticle layer ruptures, inducing the production of secondary protective tissue - the cork layer (i.e., fruit russeting), to further strengthen the protective effect on the fruit. Therefore, the formation of fruit russeting is the result of a physiological protective response produced when epidermal cells encounter stress. Cork tissue produced by suberization of epidermal cells or division of subepidermal cells.

External factors: The external factors causing Huangjin pear fruit russeting can be summarized as follows: imbalanced tree nutrition, such as excessive nitrogen application in the middle and late stages of fruit enlargement, which enriches the protein and amino acid content in the fruit, prompting rapid fruit enlargement; because the fruit epidermal cells and cuticle layer cannot keep up with the speed of fruit enlargement, cracking occurs and russet spots form; the orchard does not adopt cultivation methods such as trellis systems, cannot fix branches, and young fruit surfaces are subjected to branch sweeping and leaf rubbing, forming fruit russeting; the orchard is overcrowded, with excessive branch volume in the canopy and poor ventilation and light penetration; irrational pesticide use during the young fruit stage, with too many sprayings and too many mixed varieties, and excessive nozzle pressure during spraying causing mechanical damage to young fruit; bagging too late, with young fruit exposed for too long; poor quality fruit bags, causing bags to be damaged by rain erosion, and after absorbing water the bags become damp and do not dry easily; meanwhile, pesticide solution and rainwater easily penetrate the bag to stimulate the fruit surface, forming fruit russeting; non-standard bagging operations, with fruit bags closely adhering to the young fruit surface or bag openings not tightly sealed, fruit bags being blown by wind and rubbing the fruit surface, while rainwater and pesticide solution easily enter the bag, forming fruit russeting.

2. Technical measures to prevent the occurrence of Huangjin pear fruit russeting

Adopt trellis cultivation: Standard trellises or simple trellises such as bamboo pole frames can be used, with the trellis surface height controlled at 1.8-2.0 m. Branches are tied and bound by hanging, with clear layers between branches and reasonable layout, making use of ventilation and light penetration in the orchard. At the same time, all pear fruits are below the trellis, avoiding branch rubbing and leaf sweeping.

Strengthen cultivation management: On the basis of heavy application of organic fertilizer, carry out formula fertilization based on leaf and soil analysis. According to the actual situation of our city, for every 100 kg of fruit produced, 1 kg each of pure N, P, and K needs to be applied, along with appropriate supplementation of microfertilizers such as iron, zinc, boron, and calcium. Plant grass between orchard rows or cover grass on tree disks. Carry out artificial pollination, @#@255@#@ or mason bee pollination to ensure full fertilization. Carefully thin flowers and fruits, selecting and retaining young fruits with regular shape, smooth and glossy color, thick and long fruit stalks, growing on both sides of branches and shaded by leaves. In the same inflorescence, generally select and retain 1 fruit from the 2nd to 4th sequential positions from the base, and remove all others. Reasonable load: for trees in full fruit period, the yield per 667 sq m should be controlled at 2500-3000 kg. The above measures can make tree growth robust, fruit growth and development coordinated, and enhance the resistance of young fruits to adverse external environments.

Careful pruning: In shaping and pruning, open-center form is suitable for large trees that have been top-grafted, and spindle form and other tree forms can also be used for newly planted young trees. During shaping and pruning, attention should be paid to combining winter and summer pruning and using flexible methods such as thinning, heading, and leaving unpruned. After winter pruning, the branch volume per 667 sq m should be controlled at 35,000-40,000. Pruning should be meticulous, and attention should be paid to renewing fruiting branch groups, retaining strong branches for fruiting. Generally remove thin branches, weak branches, weak flower buds, and axillary flower buds. Flowering branches should account for about 30% of the total branch volume. Excess flowering branches can be pruned by breaking flower buds to transform them into fruiting branches for the next year.

Scientific pesticide use before bagging: Since the young fruit stage is the sensitive period for fruit russeting occurrence, from fruit set to before bagging of Huangjin pear, pollution-free fungicides and insecticides that are highly effective and have no or little irritation to the fruit peel should be selected, such as Daconil M-45, thiophanate-methyl (pure), carbendazim (pure), Xinsheng, polyoxin, imidacloprid, etc. Do not use pesticides irritating to the fruit peel, such as copper preparations, thiram-type products, mancozeb-type products, etc.; the number of pesticide types used should not exceed three, and the concentration should be as low as possible; during spraying, the atomization degree should be fine, and the nozzle should not be too close to the fruit surface or stay too long; water for mixing pesticides should not use high-hardness well water or polluted river water; spraying time should be at 9-10 am or 4-6 pm, avoiding times when the fruit surface has dew and the midday sun. Bagging can be carried out after the pesticide solution dries.

Young fruit bagging techniques: ① Bagging time: Using the double bagging technique, small wax bags should be put on starting 10-15 days after flower drop. Forty days after the first small bagging, do not remove the small bag, and directly put on the large bag. Alternatively, only bag once with a 3-layer paper bag, and the bagging task should be completed 15-30 days after flower drop. ② Bag types: The reason bagging can prevent the formation of fruit russeting is that it weakens the stimulation intensity of external adverse conditions, so great attention should be paid to selecting fruit bag quality. It is best to purchase regular, brand-name paper bags. For those using double bagging, the small bag is a milky white wax bag, and the large bag is a high-quality wood pulp paper double-layer bag. For those using single bagging, a 3-layer bag with an outer layer of yellow wood pulp paper, a middle layer of double-sided black paper, and an inner layer of cotton paper can be selected. The inner cotton paper should be smooth and soft in texture to prevent scratching the young fruit during bagging. ③ Strict bagging operation: When bagging, the bag should be puffed up, the fruit should hang suspended inside the bag, and the bag opening should be tightly sealed to prevent being blown off by strong wind, water and pesticide penetration, russeting of the fruit stalk, and hiding of pests, etc. ④ Spraying once before putting on small bags can last for 3 days of bagging; if exceeding 3 days or encountering rain, re-spray.