Cucumber scab is currently a major plant quarantine concern in domestic agriculture. This disease affects various melon crops, including zucchini, gourds, and watermelons. It is a serious pathogen that requires strict control to prevent its spread and minimize economic losses.
The disease can occur throughout the entire growth cycle of the plant, affecting leaves, stems, fruits, and especially the growing tips of young plants. When seedlings are infected, true leaves are more vulnerable than cotyledons. The first symptoms on cotyledons appear as yellowish-white round spots, which eventually cause the leaves to wither and die. On young stems, the infection starts as dark green, water-soaked diamond-shaped lesions that gradually darken and crack. Under high humidity, a gray-black mold develops—this is the conidiophores and spores of the pathogen. Tendrils may show brown rot when infected. If the growing point is affected, it may rot within 2-3 days, forming a bald patch.
At the early stage, the leaves display brownish-green, round spots that gradually expand into yellow-white, nearly circular areas. After 1-2 days, the spots dry out, and the holes formed after perforation have irregular edges, slightly wrinkled, and often appear star-shaped with a yellow halo. Infected petioles and vines develop sunken lesions that crack easily and are covered with a layer of gray-black mold. When the fruit is infected, the initial symptom is oozing of a sticky substance, followed by the formation of dark green, sunken spots. The affected area becomes shriveled, often covered with a gray-black mold layer, and the fruit stops growing, leading to malformed produce. Later, the fruit cracks, rots, and exudes a white jelly-like substance. The tissue turns amber and eventually falls off.
To manage cucumber scab effectively, strict quarantine measures must be implemented to prevent the introduction of infected seeds or plant materials. Avoid introducing seedlings from infected areas, and if any diseased plants are found, remove them immediately and dispose of them 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 treat them with a 50% carbendazim solution diluted at 700 times for 5 hours. Alternatively, soak seeds in a 0.1% carbendazim hydrochloride solution for a few hours, followed by rinsing and sowing.
Crop rotation is another effective strategy. Rotate with non-melon crops for 3–4 years. For seedbed disinfection, fumigate greenhouses with sulfur powder. Mix 2–3 grams of sulfur and 4–5 grams of sawdust per cubic meter, ignite it, and let it smolder overnight in a closed space.
Cultural practices play a key role in prevention. Apply sufficient base fertilizer, increase phosphorus and potassium levels, and cultivate strong, healthy seedlings. Use raised beds and mulch to reduce humidity inside the greenhouse. Proper planting density, removal of old leaves, and good ventilation are also important. Diseased plants should be removed and burned outside the greenhouse.
Chemical control involves spraying fungicides such as 50% carbendazim WP diluted 1000 times combined with 80% Green Hunter Manson Zn WP diluted 1000 times, or other options like 50% HT sterilizer, 80% carbendazim, 50% Cucumber WP, 75% chlorothalonil, 80% Green Hunter No. 9 WP, 20% Fuqing Wettable Powder, 12.5% myclobutanil, or 8% Luminol microemulsion. Each spray should cover about 60 kg per mu, and applications should be done every 7–10 days. Note that the last three fungicides should only be used twice per crop to avoid phytotoxicity.
Additionally, irrigation or foliar application of 50% DT fungicide (500 times), 60% DTM fungicide (400–500 times), or 86.2% copper master (1000 times) can provide effective control. These methods help reduce disease incidence and protect crop yield.
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