Detailed Explanation of Key Management Techniques Before and After Apple Bag Removal

Fruit management before and after apple bag removal is an important task before apple harvest. Many fruit growers, due to insufficient understanding, lack of attention, or unfamiliarity with its management techniques, often end up with dirty fruit surfaces, rampant pests and diseases, and a greatly reduced rate of marketable fruit. Therefore, doing a good job of apple bag removal and the management before and after bag removal is an important part of ensuring the economic benefits of the whole year.

I. Timing of Bag Removal

Removing bags at the right time is a technical measure for obtaining high-quality fruit. If bags are removed too early, the fruit is exposed for a long time and subjected to wind, rain, and sun, making the fruit surface prone to roughness and uneven coloring; prolonged sun exposure darkens the color and easily causes pest and disease damage. If bags are removed too late, the fruit receives light for too short a time, resulting in incomplete coloring, pale color, low sugar content, and poor flavor, and over time the color easily fades. The suitable timing for bag removal is: for yellow and green varieties, bags should be removed 5-7 days before harvest; for red mid-season and mid-late-season varieties, bags should be removed about 15 days before harvest; for red late-season varieties such as Red Fuji, bags should be removed 20-30 days before harvest. The timing of bag removal should also be appropriately advanced or delayed according to market demand.

Bag removal is best carried out on cloudy or partly cloudy days. If bags are removed on a sunny day, the bags on the east and north sides of the canopy should be removed between 9-12 a.m., and the bags on the west and south sides of the canopy between 3-6 p.m., which can reduce the occurrence of sunburn caused by drastic changes in light intensity.

II. Bag Removal Methods

For apples bagged with film bags, there is no need to remove the bags; they can be stored and sold with the bags on. For single-layer paper bags and inner-outer integrated bags, before 12 a.m. and after 4 p.m., the bottom of the bag should first be opened for ventilation, or the bag should be torn into umbrella-shaped strips covering the fruit, and after 4-6 days, the bag should then be removed.

Methods for removing double-layer paper bags. For double-layer paper bags with a red inner layer, first remove the outer bag, and after 5-7 sunny days, remove the inner bag between 10 a.m. and 4 p.m. to avoid excessive temperature variation on the fruit surface. If cloudy weather occurs, the time for removing the inner bag should be postponed, so as to prevent chlorophyll from forming again on the fruit surface after bag removal and affecting the coloring effect. For double-layer bags with a black inner layer, first tear open the bottom opening of the outer bag, take out the inner black bag, then tear the outer bag into strips covering the fruit, and after 6-7 days, remove the outer bag. For apples double-bagged with paper and film, only the outer paper bag is removed, and the inner film bag is retained until the fruit is sold.

III. Management Before and After Bag Removal

There are two main management tasks before and after fruit bag removal: first, promoting fruit coloring and striving for fully red fruit; second, preventing and controlling various pests and diseases and striving for a bright and clean fruit surface.

1. Spraying color-enhancing agents. At 40 days and 25 days before harvest, spray once each time with 200-fold dilution of Color Enhancer No. 1; the color-enhancing effect can be seen 7 days after spraying.

2. Leaf removal. Carry out leaf removal 3-5 days after bag removal. First remove leaves touching the fruit and leaves shading the fruit surface, then remove leaves within a 5 cm range around the fruit on the upper and outer parts of the canopy. Be careful to retain the petioles. Leaf removal should not be done too early or too much; the amount of leaves removed should be 10%-15% of the total on the whole tree, and must not exceed 30% at most, otherwise flower bud differentiation will be affected.

3. Fruit turning. Carry out fruit turning 4-8 days after bag removal. Within 8 days after bag removal (except on rainy days) is the coloring period for the sunny side of the fruit. Four days after bag removal, almost the entire sunny side of the fruit has colored. At this time, gently turn the fruit 180 degrees, turning the shaded side to the sunny side, and within 15-20 days, the shaded side will also color completely. Fruit turning should be done on cloudy days, partly cloudy days, or in the morning or afternoon of sunny days; avoid turning fruit at noon to prevent sunburn. For varieties with short fruit stalks and in high-altitude areas with large day-night temperature differences, fruit turning can also be done twice. First turn 90 degrees, and after 7-10 days turn another 90 degrees in the same direction.

4. Laying reflective film. Immediately after bag removal, lay a long strip of white reflective film on each side of the tree disk and the main trunk, and press it down with ropes or plastic soil bags. The reflective film can increase the average relative light intensity within the canopy by more than 70%, increase direct light within 0.5-1 m of the lower canopy by 18.6%-34.1%, increase reflected light by 5 times compared with control trees, achieve a coloring rate of 98% in the calyx depression of hanging fruit, and achieve a fully red fruit rate of 85%.

5. Pest and disease control. After fruit bagging, as the fruit continues to grow, calcium and some nutrients are heavily consumed. From bag removal to harvest, the fruit still has a period of exposure, so 2-3 days after fruit bag removal, promptly spray once with 300-fold dilution of Guomianjing to protect the fruit. If continuous rainy weather occurs after bag removal, in a rainy autumn, the fruit is prone to damage and interference from black spot disease, bitter pit, blister spot, ring rot fruit rot, fruit cracking, and so on. Two to three days after bag removal, Tianda 2116, Namixin, or Jinlishi plus heavy calcium should be sprayed for prevention. If black spots, black dots, or ring rot fruit rot have already appeared on the fruit surface after bag removal, a systemic eradicant fungicide such as polyoxin or Jinlishi can be sprayed once 2-3 days after bag removal to prevent the disease from spreading. However, spraying must be completed 25-30 days before fruit harvest. When spraying to supplement calcium, it must be sprayed onto the fruit surface, and it must be sprayed finely, evenly, and thoroughly.

Bagged fruit, due to receiving little light, has its sugar content reduced by about 1 degree. Therefore, in addition to comprehensive management measures such as applying more organic fertilizer and increasing phosphorus and potassium fertilizer, harvest can be appropriately delayed by 7-10 days to help increase sugar and coloring.

Chai Quanxi, Song Suzhi, Vocational Education Center of Gaocheng District, Shijiazhuang City