In open-field tomato cultivation, by late August and early September, the lower leaves often begin to yellow, while large, irregular brown spots appear in the middle of the leaves. These symptoms spread quickly, leading to a significant drop in yield. Some farmers took samples to research institutions for laboratory testing but found no signs of infectious pathogens. According to the author’s analysis, this issue is primarily due to poor management practices, aging root systems, and reduced nutrient absorption capacity. To address these problems, the following preventive measures are recommended:
During the seedling stage, it's important to implement shading and cooling techniques to prevent leggy growth and encourage strong root development. Fertilizer use should be minimized during this period. If organic matter is sufficient, there may be no need to apply nitrogen-based fertilizers. When transplanting, reduce the amount of chemical fertilizer used as a base fertilizer. A reasonable application would be 30–50 kg of compound fertilizer per mu. After planting, ensure proper care of the seedlings to support root establishment and overall growth.
Before planting, it's advisable to spray a soil conditioner without deep plowing, using about 200 grams per mu. This helps loosen the soil up to 30–50 cm deep, which improves root development, enhances water infiltration, and increases soil moisture retention. After watering, the moisture will quickly penetrate deeper into the soil rather than staying on the surface, reducing the risk of waterlogging or damage. In dry conditions, the deeper water reservoir can help prevent drought stress.
Additionally, it's recommended to combine insecticides and fungicides with foliar applications of essential nutrients such as potassium, boron, calcium, magnesium, iron, and zinc every 5–10 days at a concentration of approximately 0.3%. This helps correct any nutrient deficiencies effectively. Every 10–20 days, applying a plant growth regulator like natural alfalfa extract (Shuofeng 481) can enhance photosynthesis and improve the plant’s overall nutritional status, promoting healthier growth and better yields.
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