Recently, during a greenhouse inspection, the author observed the occurrence of tomato late blight in several greenhouses, particularly in Suffolk and surrounding areas of Shouguang City. The disease was severe and persistent, prompting the need for a detailed description of its symptoms and pathogenesis, as well as practical prevention and control measures.
When the disease affects the leaves, initial symptoms include water-soaked, light green lesions that gradually turn brown. Under high humidity conditions, a white mold layer appears on the lesions, with sparse mold visible on the underside of the leaves. Infected stems and petioles develop water-soaked, brown spots that eventually become dark brown and lead to plant wilting. When fruits are infected, irregular cloud-like patterns appear, starting as dark green, greasy spots and later turning dark brown or tan. The edges between healthy and diseased tissue are clearly defined. The fruit remains firm and bitter, and in moist conditions, it rots quickly, developing a black mold layer. The disease progresses rapidly, often leading to significant yield loss or total crop failure when 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%. Evening condensation significantly increases disease severity, while high temperature fluctuations and low humidity also promote infection. Overuse of nitrogen fertilizer and excessive planting density can reduce light penetration and airflow, creating an environment conducive to disease spread.
Prevention and control measures include immediate spraying when the first signs of infection are detected. Farmers are advised to use Suzhining diluted at 500 times and Lubara at 600 times, with added sea chlorophyll for better results. For severely affected areas, Rububa at 300 times and Cloud Daquan at 1000 times can be applied, with spraying every five days for two consecutive treatments. Additionally, proper fertilization based on tomato physiology and avoiding over-crowding are essential. Farmers should also avoid excessive irrigation to prevent large day-night temperature differences and leaf surface condensation, which create ideal conditions for disease outbreaks.
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