Red Fuji Apple Coloring Precautions, Harvesting Methods, and Flower and Fruit Thinning Tips

Red Fuji is the collective term for the coloring strains of Fuji selected and bred from bud (branch) mutations of the common Fuji. Late August to mid-September is the critical period for Red Fuji apple coloring. What issues should be noted for Red Fuji apple coloring? What are the harvesting methods? What tips are there for flower and fruit thinning?

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I. Six Key Elements for Red Fuji Apple Coloring

1. Nitrogen control: Generally, no more nitrogen fertilizer is applied after August. Shallow irrigation can be used to maintain relatively stable soil and air humidity.

2. Leaf removal: Remove the 1-2 old leaves covering the apple to increase the utilization rate of direct sunlight on the fruit surface.

3. Fertilization: Applying water-based fertilizer Jieneng potassium to the roots and spraying high-energy red potassium on the leaves helps coloring.

4. Film mulching: Lay silver reflective film between tree rows and plants to increase reflection intensity, so that fruits in the inner canopy and lower parts that are not easily exposed to light receive enough reflected light, significantly increasing the coloring of the fruit top and calyx depression.

5. Root protection: During the coloring period of Red Fuji apples, avoid frequent hoeing of the tree that damages shallow roots.

6. Late harvest: The timing of harvest has a great impact on apple coloring and quality. If harvested too early, the apple colors poorly and quality is inferior. Generally, 175-180 days after full bloom is the suitable harvest period. The closer to the later stage, the greater the day-night temperature difference, and the more favorable it is for fruit sugar accumulation and coloring.

II. Causes of Poor Apple Coloring

Every year when apples are marketed, some poorly colored apples can be seen. In severe cases, they are almost colorless, greatly affecting the external quality of the apples, thereby affecting sales and reducing the economic benefits of fruit growers. After investigation, the author analyzed the causes and proposed corresponding countermeasures.

1. Poor varietal characteristics

Early-introduced varieties such as Changfu No. 2 and other strains have aged and color poorly; late-selected varieties such as the Yanfu series, 2001, Red General, Yanga No. 1, Yanga No. 2 and other strains color well. It is recommended to combine the renovation of densely planted and closed orchards to update and transform varieties into new superior varieties.

2. Poor lighting

Many orchards are densely planted and closed, with deteriorated light and ventilation conditions. Fruits cannot color because they receive no light or too little light. This is a major cause of poor apple coloring. All fruits borne on inner canopy and lower skirt branches that color poorly are caused by this reason. In this situation, renovation of densely planted and closed orchards must be carried out.

Solution: First determine the permanent rows and temporary rows, or permanent trees and temporary trees. Then gradually retract the crossing and closing parts of the temporary rows or temporary trees year by year until they are completely removed, making way for the permanent rows or permanent trees. For orchards with inferior varieties, the method of top-grafting by alternate rows or alternate trees can be adopted. The transformed rows or trees are determined as permanent rows or permanent trees, and the rest are treated as temporary rows or temporary trees. When the rows or trees cross and close, gradually retract the untransformed temporary rows or temporary trees year by year until they are completely removed, making way for the top-grafted permanent rows or permanent trees. For orchards that are not dense, combine shaping to thin out excessively dense large branches, especially excessively dense and large lateral branches, optimize tree structure, and improve ventilation and light conditions.

3. Unbalanced nutrient supply

This is another important cause of poor apple coloring. The fertilizer requirement pattern of apple trees is a nitrogen-phosphorus-potassium ratio of 1:0.5:1, while the soil nutrient status in our city is low nitrogen, high phosphorus, and deficient potassium. Excess nitrogen and potassium deficiency can both lead to poor apple coloring. Magnesium deficiency can also cause chlorosis in apples. For a long time, emphasis has been placed on inorganic fertilizers over organic fertilizers, on nitrogen over phosphorus, with no or little potassium fertilizer applied, and abuse of medium and trace element fertilizers, resulting in an inability to supply various nutrients needed for fruit growth and development in a balanced manner, thus affecting fruit yield and quality.

Solution: In this situation, attach importance to the use of organic fertilizers, with organic fertilizers as the main component and inorganic fertilizers as a supplement, appropriately reduce the amount of chemical fertilizers, and pay attention to the reasonable combination of nitrogen, phosphorus, potassium and various medium and trace elements.

4. Insufficient moisture

Solution: Adequate water supply is an important ecological factor in promoting apple coloring. During the apple coloring period, if drought and rainless weather occurs, timely irrigation should be carried out to increase orchard humidity and promote fruit coloring. At the same time, good orchard humidity can also regulate the day-night temperature difference in the orchard, thereby promoting coloring. During the coloring period, if dew occurs, coloring is faster and better; if there is no dew or little dew, coloring is slower and poorer.

5. Excessive load

Excessive load not only easily leads to alternate bearing, but also reduces fruit quality. Because fruits crowd each other and block light, coloring is also incomplete.

Solution: Reasonable load. An easier method to master is the spacing fruit-setting method, that is, for large fruits, leave 2 apples at a spacing of 20-25 cm; for small fruits, leave 1 apple at a spacing of 15-20 cm. Generally, the yield per 667 sq m should be controlled at 3000-4000 kg.

6. Untimely summer and autumn pruning

The pruning task in summer and autumn is to cut off upright vigorous branches, water sprouts, excessively dense branches, crossing branches and overlapping branches, etc., to improve light and ventilation conditions, promote photosynthesis, balance tree nutrition, and reduce nutrient consumption. If not pruned or pruned too late, the above effects cannot be achieved, thus affecting coloring. This work should be completed at the latest before bag removal to promote coloring.

7. Coloring-enhancing measures such as leaf removal, fruit turning, and laying reflective film are not used well enough

Solution: After bag removal, promptly remove leaves clinging to the fruit and shading leaves so that the fruit is exposed to light. When the sunny side of the fruit colors well, turn the fruit in time and pad the fruit well so that the fruit surface colors evenly and completely. Laying reflective film can make fruits on the inner canopy and lower skirt branches of relatively dense orchards color completely, especially obviously promoting coloring at the fruit depression.

8. Poor bagging quality and failure to grasp the timing of bagging and bag removal

Inferior paper bags, due to poor shading, not resistant to rain erosion, and easily broken, cannot well inhibit chlorophyll formation and promote anthocyanin synthesis, and are not conducive to apple coloring after bag removal.

Solution: Choose high-quality double-layer paper bags with good shading and rain resistance, such as Japanese Kobayashi bags or double-layer paper bags with an outer bag yellow on the outside and black on the inside and a red inner bag. Bagging too late, and bag removal too early or too late are all unfavorable to coloring.

III. The Best Harvest Period for Apples

1. Look at peel color

For the vast majority of apple varieties, from young fruit to maturity, the peel color undergoes regular changes. For example, the ground color of the peel gradually changes from dark green to light green or yellow, etc. Some varieties color earlier, but the ground color of the peel is still green. Only when the ground color of the peel changes from green to yellow is the fruit truly mature. For some varieties, such as Golden Delicious, they can be harvested when the ground color is yellow-green. For those sold immediately after harvest, it is best to wait until the ground color turns yellow before harvesting.

2. Look at the fruit stalk

When the fruit is truly mature, an abscission layer forms between the base of the fruit stalk and the fruit branch. The fruit will fall off with a slight external force, such as being rotated or lifted.

3. Look at the fruit growth period

Under normal climate conditions, different varieties in the same region have relatively stable growth and development times, and the time required from full bloom to maturity is also relatively fixed. After full bloom, early-maturing varieties generally mature in 60-100 days, mid-maturing varieties in 100-140 days, mid-late-maturing varieties in 140-160 days, and late-maturing varieties in 160-190 days.

4. Look at seed color

During fruit development, the seeds of the fruit gradually turn brown. If the seeds have already turned brown or yellowish-brown when the fruit is opened, it indicates that the fruit is mature.

5. Look at fruit firmness

Fruit firmness refers to the firmness of the fruit after peeling. As the fruit matures, the flesh gradually becomes softer and firmness gradually decreases, while when unripe, the flesh is relatively hard.

6. Look at the fruit maturity stage

The fruit maturity stage can be divided into harvest maturity and edible maturity. Harvest maturity refers to the period when the fruit volume no longer increases, an abscission layer has formed at the base of the fruit stalk, and the fruit can fall off with a slight twist or lift, while edible maturity refers to the period when the fruit tastes best. Generally, late-maturing apple varieties reach edible maturity 3-4 weeks after harvest, while the two maturity stages of early-maturing varieties are basically the same. Therefore, for long-distance transport, early-maturing varieties often need to be harvested early.

7. Look at the climate of the year and market supply and demand

If there are natural disasters, manpower should be organized to harvest ahead of time as appropriate. According to the market supply and demand situation of that year, in order to obtain better economic benefits, harvest appropriately early or late.

In addition, the picking period for fruit bagged in paper bags should be 20-30 days before the maturity period of that fruit. On a sunny day, first tear open the outer bag for 3-5 days, then remove the fruit bag. After one week, when the sunny side of the fruit has colored, carry out coloring-promoting measures such as fruit turning, leaf removal, and laying reflective film, so that the whole fruit turns pink and can be picked. This is the best picking period for commercial color; overly heavy coloring is instead not welcomed by the market.

IV. Apple Picking Methods/Steps

1. Check the weather conditions.

During the fruit-picking period, moisture is high. Under conditions of fog, dew, and raindrops, the fruit is very easy to rot and not resistant to storage. Therefore, it is best to choose a sunny day for fruit picking, and place the picked fruit in a ventilated place to dry.

2. Pick fruit in order.

When picking fruit, it is best to first pick the fruit on the outer periphery and upper part of the canopy, then pick the fruit on the lower part and inner canopy, picking each branch clean to prevent missing any. When picking fruit, use a picking platform as much as possible and do not climb the tree, so as to protect branches, leaves, and fruit from being bruised or trampled. At the same time, when picking fruit, pick gently and unload gently to reduce losses from bruising and compression, and pay attention to protecting the fruit stalk.

3. Harvest in stages and batches.

Generally speaking, complete the harvest task in 2-3 batches. The first batch picks the well-colored, large fruits on the upper and outer parts of the canopy first; the second batch is best carried out 5-7 days later, also selecting well-colored and large fruits for harvest; then after another 5-7 days, pick all the remaining fruit on the tree. Generally, the first two batches of fruit should account for 70%-80% of the whole tree, and the last batch accounts for 20%-30%.

V. Tips for Apple Flower and Fruit Thinning

Apple flower and fruit thinning is an important step in fruit tree production. In particular, Hanfu apples have strong continuous fruiting ability, abundant flowering, and high fruit set rate, so reasonable flower and fruit thinning should be carried out according to tree age, management level, and quality requirements.

1. Flower and fruit thinning methods

(1) Flower-based fruit setting method. Thin flowers and fruits as early as possible to save tree nutrient consumption and improve fruit set rate and disease resistance. Thin out excessive and overly dense weak inflorescences according to spacing, and retain healthy inflorescences at a certain spacing; further, for the retained healthy inflorescences, retain only 1 intact central flower bud and 1 side flower bud, or 2 intact side flower buds, and thin out the other flower buds. Specific method: At the inflorescence separation stage, combined with pre-bloom pruning, according to tree vigor and variety characteristics, leave 1 inflorescence every 20-25 cm and remove all excess inflorescences. When thinning flowers, proceed from top to bottom and from inside to outside, first remove weak-branch flowers, axillary flowers, and terminal flowers, and retain more spur flowers. Then thin out the side flowers of each inflorescence, leaving only the central flower.

(2) Spacing method. Fruit thinning starts 10 days after full bloom and is carried out in stages, generally completed within 20 days. It can improve the fruit quality of that year, promote flower bud differentiation, and strengthen tree vigor. In the Donggang area, fruit thinning generally ends before June 10. When thinning fruit, flexibly determine the fruit retention amount according to tree vigor, length of bearing branches, and number of leaves. Generally, leave one fruit cluster every 20-25 cm, and leave only one central fruit per cluster. For weak trees and weak branches, leave one fruit every 25 cm and thin out all the rest. The second fruit thinning is carried out when the fruit grows to the size of a soybean grain, leaving 1-2 fruits per inflorescence, and removing small fruits, diseased and insect-damaged fruits, and deformed fruits. The third operation is final fruit setting, carried out when the apple grows to the size of a hawthorn. This time, single fruits should be retained. After fruit thinning, spray a fungicide once and then bagging can be done.

2. Precautions

(1) Operate accurately and carefully, proceeding branch by branch in the order of top to bottom and inside to outside, and take care to protect surrounding branches and leaves from damage.

(2) Carry out flower and fruit thinning according to weather conditions. If frost occurs after flower and fruit thinning, fruit set will be significantly reduced, affecting yield.

(3) In orchards with insufficient pollinizer trees and lack of pollen, fruit thinning should be the main method, and 10%-15% more than the required amount should be retained.

(4) Do not thin flowers on pollinizer trees, and retain fewer fruits after bloom.