What are the control methods for apple fruit cracking disease?
In the late stage of apple growth, fruit cracking disease is common and causes relatively serious damage, severely affecting the commercial value of apples and deserving sufficient attention. Apple fruit cracking disease is a physiological disorder caused by slow expansion of fruit flesh cells during the early drought period of apple growth, and rapid cell expansion when rain occurs in the middle and late stages of apple growth. The severity of the disease is closely related to variety, tree age and tree vigor. The Fuji variety is more severely affected; older trees and weak trees have more and more severe cases, while younger trees and vigorous trees have fewer and milder cases.
I. Causes of apple fruit cracking disease
1. Environmental conditions
Sudden changes in orchard environment such as drought, high temperature and windiness during apple growth and development are the direct triggers of fruit cracking disease. Continuous drought in spring, especially after consecutive days of high temperature and drought during the young fruit enlargement period, followed by sudden showers with high rainfall intensity and short duration, then clearing after the rain and another stretch of continuous high temperature, can lead to a major outbreak of apple fruit cracking disease. The fruit enlargement period is a critical time for fertilizer and water needs of fruit trees. If drought and high temperature occur and irrigation is not timely, it will seriously affect the development of peel cells, causing them to develop out of sync with the flesh tissue. If sudden rainfall or artificial irrigation occurs before harvest, it easily causes flesh cells to absorb water and expand, tearing the cortical tissue and forming cracks on the fruit surface. Cracks mostly occur during the rapid fruit enlargement period or near maturity.
2. Soil conditions
The soil nutrient conditions of the orchard are closely related to the occurrence of apple fruit cracking disease. Orchards with high soil organic matter content and balanced nutrients rarely experience cracking. The content and changes of calcium, boron, nitrogen, potassium and other elements in the soil are directly related to the occurrence of cracking. When soil calcium and boron content is insufficient, or nitrogen content is too high, apple fruit cracking disease worsens. Supplementing the soil with boron fertilizer and calcium fertilizer, and increasing potassium fertilizer, all help alleviate the occurrence of cracking disease. Orchards with long-term grass cover have balanced soil nutrient and water supply, and fruit cracking disease occurs less than in clean-cultivated orchards.
3. Cultivation management
Extensive orchard management, a dense canopy and poor ventilation and light penetration in the inner canopy lead to underdeveloped cuticle of the fruit peel and reduced elasticity, resulting in more severe fruit cracking disease. The sunny side of the fruit usually colors evenly and rarely cracks, while the shaded side of the fruit cracks very easily, especially the shaded area where two fruits are adjacent, which often becomes a concentrated area of cracking. Bagged fruit is also prone to cracking after bag removal if it encounters rain or extremely dry and hot weather.
II. Control measures
1. Strengthen orchard water management
Strengthening orchard water management is an effective measure to reduce the occurrence of fruit cracking disease. Where conditions permit, orchards should apply one thorough irrigation in winter or early spring as much as possible, and pay attention to irrigation during the fruit enlargement period, maintaining stable soil moisture content so that the fruit grows evenly. In places with poor water sources, orchard grass growing and water-saving irrigation techniques should be promoted, such as drip irrigation under grass cover and micro-sprinkling with grass cover, to regulate soil moisture and nitrogen supply.
2. Strengthen orchard soil management
Pay attention to the application of organic fertilizer and balanced fertilization in orchards. Spray boron fertilizer once at the flower bud stage, and spray boron fertilizer combined with pesticide spraying before bagging at the young fruit stage, plus 2 applications of calcium supplement.
3. Pay attention to comprehensive cultivation management in orchards. Dwarfing rootstock trees have significantly higher disease occurrence than standard trees. In cultivation, dwarfing trees should have the rootstock deeply buried, be heavily pruned, and have tree vigor rejuvenated. When bagging, reduce the use of single-layer low-quality paper bags and choose high-quality double-layer three-color paper bags. In particularly dry areas, paper-plus-film bags can also be chosen. When bagging, the bag opening must be tied tightly so that rainwater cannot flow along the fruit stalk into the fruit bag. During the young fruit stage, use as few pesticides as possible that irritate peel cells. Timely leaf removal, fruit turning, and laying reflective film on the ground to supplement light, promote sound peel development. Optimize tree shape, thin out excess branches, open light paths between layers, reduce low-light-efficiency canopy areas, and create favorable conditions for even coloring of fruit. When removing paper bags, avoid dry and hot, windy, and sharply changing temperature weather. For fruit bagged in plastic film bags, harvest, store and transport with the bags on.