Prevention and treatment of sunburn disease of Schisandra chinensis

1. Sunburn mainly damages fruits of schisandra chinensis. Sunburn parts often appear herpes, dry spots subsidence, leather quality, hardening spots or pulp tissue dry spots. The surface of the damaged fruit initially turns white (yellow or pink), then turns black yellow to brown. When sunburn occurred seriously, the pulp tissue appeared hollow necrotic spots, local pulp necrotic tissue appeared, and the damaged parts were easily infected by other fruit rot fungi, which caused fruit rot.

2. The direct cause of sunburn is heat injury and ultraviolet radiation injury, in which heat injury refers to sunburn caused by high temperature on the surface of fruit, which has nothing to do with light; and ultraviolet radiation injury is sunburn caused by ultraviolet rays, which will lead to cell disintegration. The occurrence of sunburn is related to many factors, such as temperature, illumination, relative humidity, wind speed, variety, fruit development period and tree vigor. Temperature and illumination are the main factors. Temperature and air temperature are important factors affecting sunburn of fruit. In sunny summer, the surface temperature of fruit can reach 40-50℃, which is much higher than the highest temperature of the day. Some scholars believe that the critical temperature of sunburn is between 30-32℃, and with the increase of ambient temperature, the time of sunburn decreases, and the harm degree of sunburn increases. (2) Light, light intensity and ultraviolet rays are important factors for sunburn of Fructus Schizandra. Under natural conditions, the fruit receiving light converts part of light energy into heat energy, thus increasing the surface temperature of the fruit. Together with the warming effect of high temperature on the fruit, the fruit surface reaches the critical temperature of sunburn, thus inducing the occurrence of sunburn.

The disease occurs from June to September, and the peak period is in summer with high temperature and strong light from July to August. It is often found in production that the peak period of fruit sunburn occurs every year always coincides with the highest temperature period of the year. Under the premise of higher temperature, if it is sunny, it is easy to cause sunburn, while the incidence rate of sunny days with lower temperature is low. The lower the relative humidity, the higher the incidence of fruit sunburn; wind speed can change the fruit temperature by regulating transpiration, breeze can reduce the fruit surface temperature and thus reduce the incidence; different varieties have different sensitivity to sunburn; fruit resistance to sunburn is different at different development stages, and with the maturity of fruit, the sensitivity to sunburn decreases; in the same orchard, the incidence of sunburn is low for strong trees and heavy for weak trees.

3. Control technology ① Strengthen cultivation management, enhance tree vigor; pay attention to prevent excessive application of nitrogen fertilizer, apply more organic fertilizer, improve soil water and fertilizer retention capacity, promote plant root system to develop in depth, improve plant early resistance.② When pruning, leave more branches and leaves properly to avoid exposing fruits to direct sunlight; adjust and determine reasonable proportion of branches and fruits and leaf-fruit ratio by thinning flowers and fruits. (3) Before the high temperature weather comes, the fruit surface temperature can be reduced by cold sprinkler irrigation, which can effectively avoid the occurrence of sunburn. 4. Bagging can reduce sunshine intensity and fruit surface temperature.