Comprehensive prevention of cucumber scab
Cucumber scab is currently a major plant quarantine concern in domestic agriculture. This disease affects various types of melon plants, including zucchini, gourds, and watermelons. It's a serious quarantine disease that requires strict control to prevent its spread.
The disease can affect the entire growth cycle of the plant, causing damage to leaves, stems, and fruits. Young leaves and growing points are particularly vulnerable. When seedlings are infected, the true leaves are more sensitive than the cotyledons. Yellow-white, round spots appear on the cotyledons, which eventually lead to leaf drying. On young stems, infection starts with water-soaked, dark green diamond-shaped spots that darken over time and crack. High humidity encourages the growth of a gray-black mold layer, consisting of conidiophores and conidia. Infected tendrils may show brownish rot. If the growing point becomes infected, it can rot within 2-3 days, forming a bald spot.
Initially, the leaves show brownish-green, round spots that gradually expand into yellow-white lesions. These spots become dry, with irregular edges and a star-like appearance, often surrounded by a yellow halo. Infected petioles and vines develop sunken, cracked areas covered with a gray-black mold. When the fruit is affected, it begins to exude a sticky substance, leading to dark green depressions, softening, and eventual cracking. The fruit may ooze a white jelly-like substance, turn amber, and eventually fall off.
To manage cucumber scab, strict quarantine measures are essential to prevent the introduction of infected seeds or plants. Infected seedlings should be removed immediately and disposed of outside the greenhouse. Avoid using nursery areas where scab symptoms have been observed.
Seed disinfection is also important. 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 3-4 hours, followed by rinsing and sowing.
Crop rotation with non-melon crops for 3-4 years is recommended. Greenhouses can be disinfected using sulfur powder fumigation before planting. Mix 2-3 grams of sulfur and 4-5 grams of sawdust per cubic meter, ignite the mixture, and let it smoke overnight while keeping the greenhouse closed.
Cultural practices include applying sufficient base fertilizer, increasing phosphorus and potassium levels, and promoting strong seedlings. Proper ridge formation and mulching help reduce moisture in the greenhouse. Maintain proper plant density, remove old leaves, and ensure good ventilation. Infected plants should be removed and burned outside the greenhouse.
Chemical control involves spraying solutions such as 50% carbendazim WP at 1000 times dilution combined with 80% Zn WP at 1000 times, or 50% HT sterilizer, 80% carbendazim, 50% Cucumber WP, 75% chlorothalonil, 80% Green Hunter No. 9, 20% Fuqing wettable powder, 12.5% myclobutanil, or 8% Luminol microemulsion. Apply 60 kg per mu, repeating every 7-10 days. Note that the last three chemicals should only be used twice per crop to avoid phytotoxicity.
Other effective treatments include 50% DT fungicide at 500 times, 60% DTM at 400-500 times, or 86.2% copper master at 1000 times, either sprayed or irrigated. These options provide excellent control when used properly.
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