Recently, while conducting a greenhouse inspection, the author discovered an outbreak of tomato late blight in several greenhouses, particularly in Suffolk and surrounding areas of Shouguang City. The disease has been persistent and severe, prompting the need for a detailed description of its symptoms, causes, and effective control measures.
In the early stages, infected tomato leaves show water-soaked, light green lesions that gradually turn brown. Under high humidity conditions, a white mold layer develops on the leaf surfaces, while a sparse white mold appears on the underside. When stems and petioles are affected, dark brown, water-soaked lesions form, leading to sunken areas that eventually rot, causing the plant to wilt. Infected fruits display irregular, cloudy patterns initially appearing as dark green, greasy spots, which later turn dark brown or tan. The edges between healthy and diseased tissue are clearly visible. The fruit remains firm and bitter, but under moist conditions, it begins to rot, with a black mold layer forming on the surface. This disease progresses rapidly, often resulting in significant yield loss or total crop failure if left unchecked.
The pathogen spreads quickly under favorable conditions, entering the plant through stomata or the epidermis. The ideal temperature range for disease development is 18–22°C, with air humidity above 95%. Disease outbreaks are more severe when condensation occurs in the evening. High temperature fluctuations and low humidity also contribute to the spread of the disease. Additionally, excessive nitrogen fertilizer and overcrowded planting can reduce air circulation and light penetration, creating an environment conducive to infection.
To prevent and control the disease, the following measures are recommended:
1. As soon as a central diseased plant is identified, immediate spraying is necessary. It is advised that most vegetable farmers use Suzhining diluted at 500 times and Lubara at 600 times, with added sea chlorophyll for better results. For severely infected areas, a stronger solution of Rububa at 300 times and Cloud Daquan at 1000 times can be applied. Spraying should be done every five days, with two consecutive treatments typically sufficient to control the disease.
2. Based on the physiological needs of tomatoes, proper fertilization should be practiced, avoiding over-fertilization with nitrogen. Planting density should be managed to ensure good ventilation and light exposure. Avoid excessive irrigation to prevent large day-night temperature differences, which can cause leaf surface condensation and promote disease development.
By implementing these preventive and control strategies, farmers can significantly reduce the impact of tomato late blight and protect their crops effectively.
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