What are the causes of pomegranate fruit cracking and the control methods?

Pomegranate fruit is rich in nutrients, with vitamin C content one to two times higher than that of apples and pears, making it very popular. During cultivation, fruit cracking often occurs, causing economic losses to fruit growers. So what is pomegranate fruit cracking? What to do? How to prevent it?

1. Why pomegranates crack

1. Variety: Pomegranate varieties under different cultivation conditions all show fruit cracking. Generally, mid-season varieties whose ripening period coincides with the rainy season, with large fruit, thin and smooth skin, and red-and-white skin, are prone to cracking. Examples include Yicheng red-skin pomegranate, and Shaanxi Lintong's Tianhongdan and Pink Sweet pomegranate.

2. Soil and fertilizer: Clay soil, black soil, acid white mud soil, and clay in low-lying areas retain more water and have poor aeration, resulting not only in poor fruit quality but also in easy fruit cracking. Applying excessive nitrogen fertilizer or inorganic fertilizer, deficiency of trace elements such as Ca, K and B, severe soil erosion, and soil compaction can easily cause fruit cracking.

3. Moisture: During the ripening period, excessive soil humidity or excessive fluctuation in humidity, such as high temperatures, drought, sudden heavy rain or continuous rainy days, causes the fruit to absorb too much water and crack easily. Excessive air humidity can also cause fruit cracking.

4. Temperature: Temperature and humidity changes are correlated to a certain extent. Fruit rapidly expands under high temperature and high humidity, and a sudden drop in temperature can easily cause cracking.

5. Light: Improper pruning during the growing season, with part of the fruit exposed to the sun, or a large day-night temperature difference or rain soaking, can easily cause cracking, and the cracks are often on the sun-facing side.

6. Growth period: Cracking generally occurs during the late fruit expansion stage and the ripening stage (color-turning stage), and is more severe when rainy weather or cooling occurs.

7. Harvesting: Harvesting in the early morning when temperatures are lower or after rain, harvesting when overripe, and bumping during harvesting and transport can all easily cause cracking. Pomegranate fruit cracking is often caused by a combination of various factors, especially during the mid-to-late expansion stage, when material accumulation and transformation are taking place and the seeds expand rapidly. The seed pulp cells have large vacuoles, a loose structure, strong water absorption, and a high expansion rate, while the skin gradually becomes thinner. The skin cells are small and dense with a low expansion rate, and at this time the fiberization is insufficient, making the texture crisp and tender. If this coincides with high temperature and drought followed by sudden heavy rain, continuous rainy days or cooling, cracking results. Variety is a genetic factor and is the decisive factor in pomegranate fruit cracking. Ripe pomegranates crack very easily, and the more cracked the pomegranate, the more delicious the seeds; various birds compete to peck at them, allowing the pomegranate's offspring to spread everywhere, which is also the result of natural selection.

2. Control of pomegranate fruit cracking

1. Variety selection:

Early-maturing or late-maturing varieties with medium fruit size, green skin, copper shell, thicker skin, and rough skin with rusty color are less prone to cracking. Examples include Zaozhuang Yicheng's Daqingpi and Qingpicao. In addition, Dahongpao is also less prone to cracking because of its thicker skin. Others such as Anhui Huaiyuan's Qingpi pomegranate are also excellent varieties with relatively little cracking.

2. Soil:

Yicheng pomegranates are best grown on mid-to-high terrain, on the middle and lower slopes of sunny mountain sides, in deep, slightly clayey yellow loam soil. This kind of soil has good water and air permeability and rich mineral content, and the fruit produced is of superior quality and less prone to cracking. Other suitable soil types include oil sandy soil and calcareous loam.

3. Fertilizer:

Increase the application of organic fertilizer, such as farmyard manure including pig manure, chicken and duck manure, and green manure. For inorganic fertilizer, use formula fertilization, and apply little or no nitrogen fertilizer. During the fruit expansion period, regular spraying of 2000ppm CaCL2 solution and application of appropriate amounts of P, K and B elements help improve fruit quality and prevent cracking.

4. Reasonable pruning:

Reasonable pruning during the growing season ensures ventilation and light penetration and a strong tree vigor. The area of light spots under the canopy generally accounts for 10%-15% of the canopy projection area, and the light penetration is uniform.

During winter pruning, remove or cut back some of the larger crossing branches and overlapping branches, adjust the subordinate relationships of the main branches at all levels, and thin out and cut back dense fruiting branches and weak drooping branches on the periphery. Summer pruning mainly consists of bud removal, pinching and branch cutting. Remove useless and densely crowded buds and shoots early, promptly thin out useless water sprouts, and branches with space can be transformed into fruiting branches through pinching and twisting.

5. Hormone treatment:

During the color-turning period of pomegranate, spraying gibberellin (GA3) 50mg/L 2-3 times at intervals of 10-15 days can reduce the fruit cracking rate.

6. Irrigation and drainage:

During the pomegranate ripening period, heavy irrigation should be prohibited, and drainage should be carried out promptly on rainy days to prevent excessively high soil moisture.

Because water has a high heat capacity, it plays a certain role in regulating fruit temperature and preventing sunscald and sudden cooling. Therefore, during the fruit growth and development season, reasonable watering should be done at the right time to keep the soil moist and the temperature suitable. Especially before the fruit is about to ripen, as long as the soil moisture is moderate, watering is generally not needed. If the climate is truly dry, water should also be applied lightly and finely, and never by flood irrigation, so as to avoid excess water and excessively high soil moisture. After the rainy season, the entire pomegranate orchard should be covered with grass, 15-20 cm thick, which can also achieve the effect of temperature control and moisture retention; moreover, after the grass rots, it can increase the soil organic matter content and improve soil fertility.

7. Mulching:

Ground mulching has the effect of preventing drought and preserving temperature. It can prevent excessive soil temperature changes, narrow the temperature difference, prevent soil erosion, reduce the loss of trace elements, maintain microbial activity, increase organic matter, and make fruit cells grow uniformly, thereby preventing cracking. Mulching materials include grass mats, wheat straw, and green manure.

8. Bagging:

Bagging is one of the most effective methods to prevent fruit cracking. Bagging can prevent fruit from sun exposure and rain, and from sudden cold and sudden heat changes, has a certain buffering effect on temperature and humidity, protects the fruit, and prevents cracking. Bagging can also improve fruit quality, making the flesh tender and coloring good, and can prevent infection by diseases and pests. Bagging is generally carried out during the young fruit stage. The materials used can be waste newspaper, kraft paper or parchment paper bags, or special fruit bags for bagging can be purchased directly. In addition, attention should also be paid to controlling fruit-boring pests. For example, to control the peach fruit borer, spray 20% fenvalerate emulsifiable concentrate 2000 times 2-3 times during the flowering and fruiting period, or use a cotton ball dipped in 80% dichlorvos emulsifiable concentrate and insert it into the pomegranate flower calyx tube.

9. Timely control of fruit-boring pests:

The main fruit-boring pests are the peach fruit borer and the peach fruit moth. Control measures: First, seize the three key periods of overwintering larvae emerging from dormancy, adult emergence, and egg and larval hatching for concentrated control. To control overwintering larvae, granular phoxim can be spread on the ground before the larvae emerge from dormancy. During the adult occurrence period, spray 90% trichlorfon 1000 times, or 50% phoxim 1000 times, or pyrethroid pesticides 2000-3000 times for control. During the egg and larval hatching period, spray 50% fenitrothion or 90% trichlorfon 1000 times for control, with good results. Promptly pick up and remove damaged fruit and dispose of them to reduce the source of pests. Second, before the larvae bore into the fruit, use 50% phoxim or 90% trichlorfon 0.5 kg plus 10 kg water mixed into a medicinal paste for control. Third, bag the fruit. Bagging before egg laying not only prevents larvae from boring into the fruit, but also controls multiple diseases and improves fruit quality.