What to Do About Severe Fruit Russeting in 'Hwangkeum' Pears? Causes and Control Measures

1. Causes of severe russeting in bagged fruit

1.1 Improper pesticide use during the young fruit stage. 'Hwangkeum' pears are sensitive to pesticides during the young fruit stage, which is very different from the management of 'Yali' pears. If the pesticide application procedures for 'Yali' pears are followed, russeting is bound to occur.

1.2 Orchard crowding, excessive canopy branch density, and poor ventilation and light penetration lead to russeting. At present, most pear orchards in our area are high-density orchards developed in recent years, with spacing mostly 4 m x 4 m or 3 m x 4 m, and trees about 15 years old. In pursuit of early bearing and high yield, the high-yielding tree form used for 'Yali' pears has been adopted, resulting in a top-heavy tree with excessive retained branches, which makes the orchard air humidity, especially inside the canopy, too high and lasting too long. In this humid environment, physiological factors and the synergistic effect of pesticide residues on the fruit surface aggravate russeting in bagged 'Hwangkeum' pears.

1.3 Poor fruit bag quality and non-standard operation. Poor-quality fruit bags often fail to resist rain wash and break, and once the bags absorb water and become damp, they dry slowly; at the same time, pesticide solution easily penetrates the bag and irritates the fruit surface, causing russeting. Non-standard operation mainly shows as the bag not being puffed up after bagging, with the paper bag clinging tightly to the young fruit, which easily causes rough fruit surface or russeting. If the bag opening is not tightly tied, the bag is easily blown by wind and rubs against the fruit surface, and at the same time pesticide solution and rainwater easily enter, causing russeting.

1.4 Other causes. In addition to the above causes, bagging too late leaves the young fruit exposed for too long; not adopting cultivation methods such as trellis systems means branches cannot be fixed, and the young fruit surface is severely rubbed by wind, producing russeted fruit.

2. Technical measures to reduce russeting in 'Hwangkeum' pears

2.1 Adopt a trellis cultivation method. A standard trellis or simple trellis can be used to train and fix branches. Pay attention to bending branches so that the basal angle is kept at about 60°.

2.2 Prune carefully and open the light path. In training and pruning, for large top-grafted trees it is advisable to use an open-center form to facilitate ventilation and light penetration; a spindle form and other tree forms may also be used, but the principles to follow in training and pruning are: (1) control top dominance; (2) use single-axis extension for peripheral extension shoots, and prune back the leader (if the terminal bud of 'Hwangkeum' pear is not removed, 4-6 new shoots will emerge from the branch tip), thin out peripheral branches, suppress the front and promote the rear, improve ventilation and light penetration, and prevent the inner canopy from becoming bare and weak; (3) remove excessively dense scaffold branches and branches on the upper and lower sides of limbs, and retain more slanted branches on both sides.

2.3 Scientific pesticide use. To reduce pesticide use during the young fruit stage, the occurrence of pests and diseases must be controlled. In addition to measures such as orchard sanitation and bark scraping, pesticide application before flowering can effectively control pests and diseases, and after flowering pesticide use should be reduced. Spray mineral oil emulsion once in early March, an insecticide once in mid-March, lime sulfur mixture once in late March, and an insecticide plus fungicide once at the balloon stage of flower buds, spraying heavily and finely to reduce pest population density. After petal fall, in principle do not apply pesticide immediately; wait until May and apply pesticide once before bagging with small bags. The principles to follow for pesticide use during the young fruit stage of 'Hwangkeum' pears are: (1) use as little pesticide as possible, or even none; (2) use as low a concentration as possible, and mix as few pesticide types as possible; (3) do not use drenching sprays; the pesticide should be atomized, and under the premise of achieving control efficacy, spray as lightly as possible; (4) water-based and powder formulations are preferable, do not use emulsifiable concentrates, and do not use pesticides that irritate the fruit skin, such as copper formulations, thiram-type products, mancozeb-type products, and emulsifiable concentrate formulations; when spraying, the droplets should be fine, the nozzle should not be too close to the fruit surface, and the concentration should not be too high.

2.4 Bagging technique. (1) Choose high-quality fruit bags and buy regular brand-name fruit bags. 'Hwangkeum' pear is a green-skinned cultivar; to meet export standards it needs two rounds of bagging: first a small white wax bag (specification: 10 cm long, 7 cm wide), then a double-layer large paper bag (available in two types, yellow outside and white inside, or yellow outside and red inside; specification: 20 cm long, 15.5 cm wide). (2) The bagging period starts 10-15 days after petal fall and ends before the epidermal hairs of the young fruit fall off. In ordinary years, the time for bagging with small bags is May 1-10; the first bagging (large bags) should preferably be completed about 60 days after petal fall, generally completed around wheat harvest. Before bagging with large bags, the small white wax bags do not need to be removed. (3) Strictly follow bagging operations; when bagging, the bag should be puffed up, the drainage and ventilation holes at the two bottom corners of the bag should be opened, and the bag opening should be tightly tied and must not face upward, so as to prevent rainwater and pesticide solution from flowing into the bag. (4) Spraying pesticide once before bagging with small bags can allow bagging to be maintained for 3 days; if more than 3 days pass or rain occurs, re-spray.

Through the above measures, the problem of severe russeting in 'Hwangkeum' pears can be effectively solved, the rate of good fruit can reach more than 70%, greatly improving the economic benefits of planting 'Hwangkeum' pears, increasing production and income.