Comprehensive prevention of cucumber scab
Cucumber scab is currently a key plant quarantine concern in domestic agriculture. This disease affects various melon crops, including zucchini, gourds, and watermelons. It's a serious pathogen that needs to be controlled effectively to avoid economic losses and prevent the spread of infection.
The symptoms of cucumber scab can appear throughout the entire growth cycle. The disease mainly damages leaves, stems, and fruits, with young growing points being the most vulnerable. When seedlings are infected, true leaves are more susceptible than cotyledons. Yellow-white round spots may develop on the cotyledons, which eventually lead to leaf drying. On young stems, the infection starts as dark green, water-soaked diamond-shaped spots that darken and crack. High humidity encourages the formation of a gray-black mold layer—this is the conidiophores and spores of the pathogen. Infected tendrils may turn brown and rot. If the growing point becomes infected, it can rot within 2-3 days, forming a bald patch.
At the early stage, the leaves show brownish-green, round spots that gradually grow into yellow-white, nearly circular lesions. After 1-2 days, these spots dry out, and the holes formed after perforation have irregular edges, slightly wrinkled, and resemble a star shape with a yellow halo. When petioles or vines are infected, the affected areas become sunken and form sores that easily crack, often covered with a gray-black mold. On the fruit, the disease begins with oozing gum, followed by dark green sunken spots, leading to shriveling and the formation of deformed fruits. Eventually, the fruit cracks, rots, and exudes a white jelly-like substance. The tissue turns amber and falls off.
To manage cucumber scab, 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, remove them immediately and dispose of them outside the greenhouse. Do not use contaminated nursery sites.
Seed disinfection is also crucial. Soak seeds in 50°C water for 15 minutes, then soak in a 700-fold dilution of 50% carbendazim for 5 hours. Alternatively, soak in a 0.1% carbendazim hydrochloride solution for several hours, followed by rinsing in clean water for 3-4 hours before sowing.
Crop rotation is another effective strategy. Rotate with non-melon crops for 3-4 years. For greenhouse seedbeds, fumigate with sulfur powder. Before planting, mix 2-3 grams of sulfur and 4-5 grams of sawdust per cubic meter, ignite in several places, and leave the greenhouse closed overnight to allow the smoke to work.
Good cultivation practices include applying sufficient base fertilizer, especially phosphorus and potassium, to promote strong seedlings and enhance resistance. Use raised beds and mulch to reduce humidity inside the greenhouse. Proper spacing, removal of old leaves, and adequate ventilation are also important. Infected plants should be removed and burned outside the greenhouse.
Chemical control options include spraying solutions such as 50% carbendazim WP at 1000 times, 80% Green Hunter Manson Zn WP at 1000 times, or 50% HT sterilizer at 1000 times. Other options include 80% carbendazim, 50% Cucumber WP at 700 times, 75% chlorothalonil at 600 times, or 80% Green Hunter No. 9 WP at 700 times. Additionally, 20% Fuqing Wettable Powder at 2500–3000 times, 12.5% myclobutanil at 4500–5000 times, or 8% Luminol emulsion at 900–1000 times can be used. Apply 60 kg of solution per mu, spraying every 7–10 days. Most of these fungicides can be alternated for 3–4 consecutive applications. However, the last three types should only be sprayed twice per crop to avoid phytotoxicity.
In addition, 50% DT fungicide at 500 times, 60% DTM fungicide at 400–500 times, or 86.2% copper master at 1000 times can be used for irrigation or spraying, showing good efficacy against the disease.
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