Cucumber scab is currently a key plant quarantine disease in domestic agriculture. This fungal disease affects a wide range of cucurbit crops, including zucchini, gourds, and melons. It is a serious threat to the production of these vegetables and requires strict control measures.
The symptoms of cucumber scab can appear throughout the entire growth period of the plant. The disease primarily affects leaves, stems, and fruits, with the youngest growing points being most vulnerable. When seedlings are infected, the true leaves are more susceptible than the cotyledons. Initially, yellow-white circular spots appear on the cotyledons, which eventually cause the leaves to dry up. On young stems, the infection starts as water-soaked, dark green diamond-shaped lesions that gradually darken and crack. In high humidity conditions, a gray-black mold layer develops, consisting of the pathogen's conidiophores and conidia. Infected tendrils may develop brown rot. If the growing point is infected, it can rot within 2-3 days, forming a bald spot.
At the early stage of the disease, the leaves show brownish-green, round spots that resemble star shapes. These spots expand over time, turning into yellow-white, nearly round areas. After 1-2 days, the spots dry out, and the holes formed after perforation have irregular edges, slightly wrinkled, and star-shaped with a yellow halo. When petioles or vines become infected, the affected area becomes sunken, forming sores that crack easily, often covered with a gray-black mold layer. Infected fruits first exude a sticky substance, then develop dark green depressions, becoming shriveled and often covered with a gray-black mold layer. The diseased part stops growing, leading to deformed fruits. Later, the fruits crack and rot, exuding a white jelly-like substance. The tissue turns amber and eventually falls off.
To manage this disease, strict quarantine measures must be implemented to prevent the introduction of infected seeds and plants. Avoid bringing in seedlings from infected areas. If any infected plants are found, they should be removed immediately and disposed of outside the greenhouse. Do not use nursery areas where scab has been detected.
Seed treatment is also essential. Soak seeds in 50°C water for 15 minutes, then soak them in a 50% carbendazim solution (700 times dilution) for 5 hours. Alternatively, use a 0.1% carbendazim hydrochloride solution for 4 hours, followed by rinsing in clean water for 3–4 hours before sowing.
Crop rotation is an effective method. Rotate with non-cucurbit crops for 3–4 years. For seedbed disinfection, fumigate greenhouses with sulfur powder mixed with sawdust. Place 2–3 grams of sulfur and 4–5 grams of sawdust per cubic meter, ignite and leave the greenhouse closed overnight to ensure proper fumigation.
Cultural practices such as applying sufficient base fertilizer, increasing phosphorus and potassium levels, and cultivating strong seedlings can enhance plant resistance. Proper ridge planting, mulching, and reducing air and soil moisture help prevent disease spread. Prune old leaves, maintain proper plant density, and ensure good ventilation and temperature control in the greenhouse. Remove and burn all infected plant parts outside the greenhouse.
Chemical control is another important measure. Spraying solutions like 50% carbendazim WP at 1000 times, 80% Green Hunter Manson Zn WP at 1000 times, or 50% HT sterilizer at 1000 times can be effective. Other options include 80% carbendazim, 50% Cucumber WP at 700 times, 75% chlorothalonil at 600 times, 80% Green Hunter No. 9 WP at 700 times, 20% Fuqing wettable powder at 2500–3000 times, 12.5% myclobutanil at 4500–5000 times, or 8% Luminol emulsion at 900–1000 times. Apply 60 kg per mu, spraying every 7–10 days. Note that the last three products should only be used twice per crop to avoid phytotoxicity. Other fungicides can be alternated for 3–4 applications.
Additionally, using 50% DT fungicide at 500 times, 60% DTM fungicide at 400–500 times, or 86.2% copper master at 1000 times through irrigation or spraying can also provide effective control.
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