Causes of Severe Cracking in Bagged Apples and Control Methods

Bagging technology has been widely applied in apple cultivation. It not only reduces damage to apples from pests and diseases, but also lowers pesticide residues, greatly improving fruit quality and commercial value. However, some fruit growers using bagging technology in cultivation still find that their apples develop severe cracking. What causes this? How should it be controlled? Let's take a look together.

1. Calcium deficiency

Calcium deficiency is one of the main causes of cracking in bagged apples. Calcium is a basic element of the epidermal cells of apple fruit. Because calcium is an immobile element in the tree, its movement within the tree relies on transpiration. In bagged apples, transpiration inside the bag is far less than that of the branches and leaves, and the limited calcium is taken away by the branches and leaves. As a result, the fruit cannot obtain sufficient calcium, causing severe cracking.

Control method: Calcium supplementation is the key point for preventing cracking. Apple's demand for calcium generally has two peak periods each year. The first period is about 4 weeks after petal fall; the second period is during the rapid expansion of fruit cells, generally in August to September, and during this period apple's demand for calcium accounts for more than 70% of the total annual demand. Therefore, calcium should be supplemented at the right time. Generally, 0.3% to 0.4% sugar alcohol chelated calcium is sprayed multiple times during the bud break stage, after petal fall, and at the harvest stage.

2. Poor climate

Poor climate is a trigger for cracking in bagged apples. During the high-temperature summer season, many orchards lack adequate irrigation facilities and cannot irrigate in time. At the transition between summer and autumn, rainfall is abundant, and the fruit expands rapidly. The growth rate of the peel cannot keep up with the growth rate of the flesh, so cracks form on the peel surface and then develop into splits.

Control method: Fertilizer and water management should be strengthened; this is an important part of preventing cracking, especially during the fruiting period. When the climate is dry, water promptly to keep the soil moist. When rainfall is heavy, do a good job of ditching and drainage, and try to prevent the plants from absorbing large amounts of standing water.

3. Poor permeability

When permeability within the canopy is poor, moisture on the shaded side of the fruit cannot dissipate quickly, ultimately causing the cracked wounds to become suberized. In mild cases, black spots appear on the fruit; in severe cases, the fruit surface cracks into strip-shaped or horizontal wounds, and in the later stage the fruit also shrivels and splits, completely losing its commercial value. The sunlit side of the fruit often colors evenly and rarely develops cracking, while cracking on the shaded side of the fruit is relatively severe.

Control method: Through reasonable pruning, ensure good permeability and improve light transmission. Especially in some old orchards, because of extensive management and poor tree structure, tree renovation should be carried out early to improve photosynthetic utilization. Second, thin flowers and fruit at the right time, maintain a reasonable load on the tree, balance the plant's vegetative growth and reproductive growth, and reduce the uptake of calcium by branches and leaves.

4. Uneven fertilization

Many orchards apply a relatively large amount of nitrogen fertilizer while neglecting the application of phosphorus, potassium, and micronutrient fertilizers. This causes excessive vegetative growth of the tree, so that the already insufficient calcium is consumed even more in the growth of branches and leaves, making fruit cracking even more severe. If the nitrogen content is too high during the fruit expansion period, cracking will occur more quickly. The cracks initially extend along the lenticels, and later form obvious transverse cracks.

Control method: Increase the application of organic fertilizer to raise the soil organic matter content. The fertilizer should be mainly decomposed organic fertilizer, combined with an appropriate amount of phosphorus and potassium fertilizer and trace elements. Grass can also be grown between orchard rows, which can provide sufficient green manure for the fruit trees, improve soil structure, and regulate the microclimate within the orchard.

The above is an introduction to the causes of severe cracking in bagged apples and the control methods. We hope it can help you. To learn more related knowledge, please follow us.