In the greenhouses of Tengzhou, Shandong, a few days ago, farmers noticed that many bell pepper leaves were showing unusual symptoms. Some had scorched edges, others displayed yellow-green patches around the leaf area, while some had large yellow spots in the center. Additionally, small leaves near the growing tip showed multiple yellow spots. Many leaves also appeared distorted, with raised bumps or bubbles on their surfaces. Initially, some suspected a viral infection and applied various antiviral treatments. These treatments provided temporary relief for about seven days, but the problem soon returned. After a thorough investigation, several key factors were identified as causes of the leaf discoloration.
Firstly, the temperatures in February and March this year were significantly lower than in previous years, which slowed plant growth and resulted in less vibrant leaf color compared to past seasons. Secondly, many greenhouses have been used for continuous cropping for 7–8 years, leading to severe root rot and blight due to heavy yields. Affected plants showed varying degrees of yellowing and scorching. During planting, excessive compound fertilizer was applied—over 100 kilograms per acre in some cases—and the application was uneven, causing root burn and dry tips.
Thirdly, the greenhouse structure is arched and covered with straw mats, resulting in poor insulation. Nighttime temperatures often dropped below 10°C for extended periods, and ground temperatures remained low. This, combined with excessive nitrogen fertilizer use, led to an accumulation of ammonium nitrogen in the soil. This inhibited the absorption of essential nutrients like nitrate nitrogen, phosphorus, and potassium by the roots, causing nutrient deficiencies in the leaves. It also affected the uptake of micronutrients such as zinc, magnesium, calcium, and iron, leading to symptoms like calcium deficiency (leaf margin scorch), potassium deficiency (yellowing around the edges), magnesium deficiency (yellow spots in the middle), and zinc deficiency (small, curled, yellow-spotted leaves).
Fourthly, due to the low temperature, farmers hesitated to ventilate after planting, leading to high humidity inside the greenhouse. This caused leaf transpiration to slow down, reducing water absorption by the roots and limiting the transport of nutrients like nitrogen, phosphorus, potassium, zinc, boron, and calcium to the leaves. As a result, symptoms such as yellowing, scorching, and chlorosis became more visible.
Lastly, the current low temperatures make it unsuitable for viral diseases to thrive, and the symptoms are not contagious. Most antiviral sprays work by stimulating plant growth, so they may provide short-term relief, but they don’t address the underlying issues, hence the symptoms return quickly.
To prevent these leaf color abnormalities in the future, farmers should consider deep plowing before planting to a depth of at least 30 cm. This helps loosen the soil, improve root development, and enhance nutrient absorption, reducing leaf discoloration due to nutrient deficiencies. If deep plowing isn't feasible, a soil conditioner can be applied—200 grams mixed with 100 kg of water and sprayed over an acre, helping to loosen the top 50–80 cm of soil.
Applying organic fertilizers and reducing nitrogen usage is also recommended. A balanced approach would be to apply 25 kg of compound fertilizer per acre during planting, along with appropriate amounts of calcium, magnesium, and zinc. During colder months, foliar sprays every 3–5 days with 0.2% potassium dihydrogen phosphate and organic supplements like calcium, zinc, and magnesium can help meet the plant’s nutritional needs, improving its resistance to cold and disease.
Additionally, spraying 10,000 times diluted apigenin 481 every 20 days can promote photosynthesis and strengthen plant immunity. Proper ventilation and dehumidification should be maintained when possible, to reduce humidity and encourage better leaf transpiration. Finally, using high-temperature fumigation and applying fungicides like carbendazim and methyltobacillus can help prevent root rot and blight.
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