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Measures for Controlling Cucumber Sclerotinia
Experts have noted that cucumber sclerotinia is caused by the fungus *Sclerotinia sclerotiorum*, which belongs to the subphylum Ascomycota. The pathogen can survive in the soil, in plant residues, and even within seeds during winter or summer. Sclerotia, which are the hardened structures of the fungus, can remain viable for up to two years. When environmental conditions become favorable, these sclerotia germinate and produce ascospores, which are released from the ascus and spread through air currents. These spores can infect senescent leaves or unopened petals, penetrating directly through the epidermis to initiate infection. Once inside, the pathogen destroys host cells and spreads to healthy tissues, leading to repeated infections as diseased and healthy plants come into contact. Infected leaves may touch healthy ones, and fallen petals can also serve as sources of new infections. This cycle allows the pathogen to expand its reach, causing damage to stems and leaves.
Cucumber sclerotinia has a broad host range, affecting not only cucumbers but also tomatoes, bell peppers, eggplants, peas, potatoes, carrots, celery, and various cruciferous vegetables. It commonly occurs in middle tube sheds and adjacent greenhouses where cucumbers are cultivated.
The disease primarily affects the stem base and fruits, though it can also damage stems and leaves at any growth stage, from seedlings to maturity. In stem infections, the initial symptoms appear as water-soaked lesions, which turn light brown as they expand. The affected stems soften, develop longitudinal cracks, and eventually cause the vines above to wilt. High humidity leads to the formation of white, cotton-like mycelium on the infected areas. If the stem is injured, the inner tissue becomes damaged, and later, the stem becomes hollow, with white mycelium and black sclerotia appearing on the surface. These sclerotia start off white and become dark brown externally with a white interior over time. Fruit infections begin at the fruit's umbilical area, leading to rot and the development of white mycelium and black granular sclerotia. Leaf infections first show water-soaked spots, which grow into grayish-brown, irregular lesions without clear borders. The infected areas soften, and white, fluffy mycelium develops.
To prevent this disease, several measures can be taken. First, seed treatment is essential. Seeds should be soaked in 50°C warm water for 10 minutes, then immediately transferred to cold water to cool down. After drying, they can be sown, effectively killing any sclerotia present in the seeds. Second, regular field sanitation is crucial—removing old leaves, flowers, and diseased plants promptly, and burning or burying them deeply. After harvest, all diseased material must be removed, and the soil should be deeply tilled to prevent sclerotia from germinating. Third, crop rotation is recommended, alternating with aquatic crops, legumes, onions, or garlic each year. Fourth, proper management is key: controlling planting density, managing temperature and humidity in greenhouses, ensuring timely ventilation, and avoiding high humidity, especially at night. Watering should be done in the morning, and the greenhouse should be aired out regularly to reduce moisture levels. During spring, before cold weather sets in, small arch plastic films should be covered, and straw should be placed around the beds to protect plants from frost.
Fifth, seedling beds should be monitored regularly, and only strong, healthy seedlings should be transplanted. Lastly, soil disinfection using 8–10 grams of 50% carbendazim powder mixed with 10–15 kg of fine dry soil per square meter can help control the disease. Chemical control is also effective, with applications of fungicides like 43% Haldex suspension (2000–3000 times dilution), 50% quickan wettable powder (1000 times), 50% acetaminophen wettable powder (1000 times), 50% carbendazim wettable powder (800 times), and 70% thiophanate-methyl (1000 times) every 7–10 days, depending on disease severity. Multiple applications may be necessary for optimal results.