What are the control methods for sunscald in Schisandra chinensis?

1.Schisandra chinensisSunscald mainly damages the fruit. Sunscald sites often appear blistered, with sunken necrotic spots, lignification, hardened lesions, or necrotic spots in the flesh tissue. The surface of affected berries initially turns white (yellow or pink), then becomes black-yellow to brown. When sunscald is severe, sunken necrotic spots appear in the flesh tissue, with localized necrotic tissue in the flesh, and the affected areas are prone to infection by other fruit rot pathogens, causing fruit decay.

2. Disease development pattern The direct causes of sunscald are heat injury and ultraviolet radiation injury, of which heat injury refers to sunscald caused by high temperature on the fruit surface and is unrelated to light; ultraviolet radiation injury is sunscald caused by ultraviolet rays, which leads to cell disintegration. The occurrence of sunscald is related to many factors such as temperature, light, relative humidity, wind speed, variety, fruit development stage and tree vigor. Among these, temperature and light are the main influencing factors. ① Temperature: air temperature is an important factor affecting sunscald in Schisandra chinensis fruit. On sunny, high-temperature summer days, the surface temperature of Schisandra chinensis fruit can reach 40-50°C, far higher than the maximum air temperature of the day. Some scholars believe that the critical air temperature that causes sunscald is between 30-32°C, and as the ambient temperature rises, the time to sunscald occurrence shortens and the degree of sunscald damage increases accordingly. ② Light: light intensity and ultraviolet rays are important factors in the occurrence of sunscald in Schisandra chinensis fruit. Under natural conditions, fruit exposed to light converts part of the light energy into heat energy, thereby raising the fruit surface temperature; combined with the warming effect of high temperature on the fruit, this together causes the fruit surface to reach the critical temperature for sunscald, thus inducing the occurrence of fruit sunscald.

The disease occurs from June to September, with the peak incidence during the hot, high-light summer days of July to August. In production, it is often found that the peak period of fruit sunscald each year always coincides with the period of the highest temperatures of the year. Under the premise of relatively high temperatures, sunny days can very easily lead to the occurrence of sunscald, while the incidence is low on sunny days with lower temperatures. The lower the relative humidity, the higher the incidence of fruit sunscald; wind speed can change fruit temperature by regulating transpiration, and a gentle breeze can lower the fruit surface temperature and thus reduce the incidence; different varieties differ in their sensitivity to sunscald; fruit differs in its resistance to sunscald at different development stages, and as the fruit matures, its sensitivity to sunscald decreases; within the same orchard, trees with strong vigor have a low incidence of sunscald, while trees with weak vigor have severe incidence.

3. Control techniques ① Strengthen cultivation management to enhance tree vigor; take care to prevent excessive application of nitrogen fertilizer, apply more organic fertilizer, improve the soil's water- and fertilizer-holding capacity, promote deeper root development, and improve the plant's drought resistance. ② When pruning, leave appropriately more branches and leaves to avoid exposing the fruit to direct sunlight; through flower and fruit thinning, regulate and determine a reasonable branch-to-fruit ratio and leaf-to-fruit ratio. ③ Before high-temperature weather arrives, cool sprinkler irrigation can be used to lower the fruit surface temperature, effectively preventing the occurrence of sunscald. ④ Using fruit bagging can reduce sunlight intensity and fruit surface temperature.