Overwintering tomato freeze injury
As winter deepens, temperatures in northern regions begin to drop significantly, putting the tomatoes grown in winter greenhouses through a harsh cold test. Tomato is a heat-loving crop with limited cold tolerance. When grown during the winter or early spring, especially during the deep winter period, they are prone to cold stress and frost damage when exposed to low temperatures or frost. If greenhouse temperatures remain between 5°C and 10°C for extended periods, the leaves may appear dark green or waterlogged. Prolonged exposure to 5°C can cause the leaf edges to lose their green color. In sudden temperature drops below 2°C, the leaves may turn purple due to increased anthocyanin production, followed by wilting and even death. When temperatures stay below 5°C for a long time, the plants suffer from cold injury, losing their green color and turning pale, eventually dying from chilling damage.
These symptoms can easily be mistaken for magnesium deficiency, which causes chlorosis due to a lack of magnesium. However, in cold winters, excessive nitrogen and phosphorus fertilizers can interfere with magnesium uptake, making magnesium deficiency more likely. Despite this, when leaf chlorosis occurs during cold seasons, the first consideration should be cold damage rather than nutrient deficiency. Prolonged exposure to temperatures below 5°C leads to chilling injury, causing leaves to become chlorotic and bleached. In severe cases, the entire plant may die. By analyzing the seasonal climate, reviewing management practices, and checking insulation measures, it's possible to differentiate between freezing injury and nutrient deficiency. Prompt treatment based on symptoms can help reduce unnecessary losses.
To address freezing damage, selecting cold-tolerant, low-light, and low-temperature varieties is essential. Strengthening greenhouse insulation is a key strategy for preventing cold injury. Improving the thickness of the earth walls, increasing the density of weeds, and using temporary arch sheds can help raise the temperature inside the greenhouse. In case of sudden frosts, temporary heating methods such as burning coal stoves or using electric heaters can be employed. For chemical control, cold-resistant agents can be applied. A solution of 3.4% Bi Protect wettable powder diluted 5000–7500 times, or a mixture of 15 liters of water, 50 grams of brown sugar, and 0.3% potassium dihydrogen phosphate, can be sprayed onto the plants to improve their resilience against cold stress.
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