Frost damage prevention and control methods and key technical points for Schisandra chinensis

1. Disease symptoms Frost damage of varying severity occurs every year in the Schisandra chinensis production areas of Northeast China. In mild cases, the branches and shoot tips are frozen; in severe cases, the entire plant dies. Affected leaves initially show irregular small spots, which over time merge together and develop into mottled, uneven large patches; the leaves fade, and the leaf margins dry up. In the later stages of the disease, the young tender shoots suffer severe water loss and wilting, the tissues dry out and become necrotic, the leaves dry up and fall off, and the tree vigor declines. The first factor is the influence of temperature: after Schisandra chinensis buds break in spring, the nighttime temperature sometimes drops sharply, and water vapor condenses into frost, causing the young tender parts to freeze. Frost is also related to topography to some extent. Because cold air has a relatively high specific gravity, low-lying land often cools down more sharply than flat land, and the cooling lasts longer. Some Schisandra chinensis orchards are easily damaged by late frost because they are located on frost channels or in ditch bottoms and valleys where cold air readily accumulates.

2. Disease occurrence pattern March to May is the peak period for this disease. There is a late frost every May in the mountainous areas of eastern Liaoning, during which Schisandra chinensis suffers extremely severe frost damage. Different Schisandra chinensis varieties differ in cold tolerance: the earlier the variety matures, the weaker its cold tolerance and the greater the yield reduction. Tree shape and tree vigor are also related to frost damage to some extent; weak trees suffer more severe freezing than vigorous trees. The more mature the branches, the higher the degree of lignification, the lower the water content, the higher the concentration of cell sap, and the more starch accumulated, the stronger the cold tolerance. Different management measures also lead to different degrees of damage: Schisandra chinensis in soil with relatively high moisture and under sprinkler irrigation suffers less damage, while orchards that are not watered suffer more severe damage.

3. Prevention and control measures ① Establish the orchard scientifically: choose a sunny gentle slope or flat land for the orchard, and avoid frost channels and valleys to prevent and reduce late frost damage. ② Ground mulching: use corn and other crop straw to mulch around the roots of Schisandra chinensis, prevent the soil from warming up, delay leaf unfolding and flowering of Schisandra chinensis, and avoid late frost damage. ③ Smoking for insulation: after Schisandra chinensis buds break, pay attention to local weather forecasts. On nights when late frost may occur, when the temperature drops to 1°C, light piles of damp branches, leaves, wood shavings, and wormwood grass, and cover them with a layer of soil to prolong the burning time. Place the smoke piles around the orchard and on the working paths. According to the wind direction, set up more smoke piles on the upwind side so that the smoke quickly fills the orchard. ④ Sprinkler irrigation for insulation: according to the weather forecast, a large amount of ground irrigation and water spraying on the plant canopy can be used for insulation. ⑤ Spraying fertilizers and chemicals: during the growing season, apply nitrogen fertilizer reasonably to promote branch growth and ensure vigorous tree growth; in the later stage, apply an appropriate amount of phosphorus fertilizer to encourage the branches to stop growing early, which helps the tissues become compact and prolongs the time for nutrient accumulation, thereby enabling better cold-hardening. Spraying antifreeze solution and phosphorus-potassium fertilizer can prevent damage from low temperatures of 2-5°C for 5-7 days.