Cucumber scab is a fungal disease of cucumber crops. When the humidity is high, gray-black mold spots will grow. Both open fields and cucumbers grown in greenhouses can be infected. The disease occurs in greenhouses. In addition to harming cucumbers, the disease can also harm crops such as pumpkins and zucchini, so you must be vigilant!
1 onset symptoms
Cucumber scab is mainly harmful to the young parts of leaves, stems and fruits, and can be infected from seedling to adult stage. After the seedlings are infected, the cotyledons produce yellow-white and nearly round small spots. After the lesions expand, they are connected to each other into irregularly shaped necrotic spots. The new leaves are withered and the plants stop growing. After the stems are infected, they are first water-stained and light green. Oval or irregular streaks, and then the cracks in the lesions are dark brown. When the disease is severe, the diseased part rots. When the humidity is high, the gray-black mold layer grows on the lesions. The lesions are star-shaped polygons in the late stage, and the diseased parts fall off. The surrounding health continues to grow, leaving a star-shaped hole with black edges; after the petiole and melon are killed, the lesions are rhomboid or long, varying in size, light yellow-brown, recessed in the middle of the disease, deep in longitudinal fissure, forming After the melon stripe disease, it begins to produce a near-circular dark green lesion, which secretes milky white rubber particles, which gradually turns amber, and then falls off after dry and hard. When the diseased part is cracked and sagged in the middle of the diseased part, the lesion stops. Expansion. The cucumber melons infected with black star disease are bent, and the black mold layer is formed in the diseased part when wet.
2 disease conditions
Cucumber scab pathogens overwinter with the mycelium or silk in the soil with the mycelium or silk. It can also attach conidia to the surface of the seed or lurk in the seed coat for wintering. It can also adhere to the gap or bracket of the greenhouse wall. Over the winter. Seeding the bacteria seeds, the bacteria can directly infect the seedlings. In the second year, the pathogen on the diseased residue in the soil can produce conidia and infect the colonized melon seedlings. After the onset of the field plants, if the conditions are appropriate, the diseased part can produce a large number of conidia, and spread by airflow, rainwater and farming operations. When the temperature and humidity conditions are suitable, the conidia will germinate quickly, invading from the wound, stomata or directly penetrating the epidermis. The optimum conditions for the development of conidia are temperature 20~22°C, relative humidity above 90%, and water film (drop) must exist. Generally, the incidence of cucumber in the solar greenhouse is heavier, and the planting density is high, the light is small, the ventilation is poor, the protected land is large, the water is heavy, the fertilizer is small, and the land is heavy.
3 Prevention measures
3.1 Seed treatment
Seeds are harvested from disease-free seedlings, disease-free seeds are selected, seeds are sterilized before sowing, and warm soup (or medicinal) should be soaked before germination. Soak for 15min with 50°C warm water for 15min or soak with 50% carbendazim WP 500 times for 20min, then wash with water to carry out germination; also use 2.5% for bleaching seed coating agent 10m L and water 150~200m L. After mixing, add 5~10kg seeds for seed dressing, seed coating and seeding.
3.2 Agricultural control
Severely developed plots are carried out with non-cucurbit crop rotation for 2~3 years; timely clearing of field diseased plants, fruit drop, diseased leaves and diseased flowers, brought to the outside of the shed for centralized destruction or deep burial treatment, can not be littered anywhere; daytime temperature control 28~30°C, 15°C at night, keep the relative humidity below 90%; strengthen ventilation, reduce the humidity in the shed, reduce the condensation on the foliage, control the watering when the cucumber is planted until the melon period; use the sulphur fumigation disinfection in the greenhouse before planting, For every 100m space, 0.25kg of sulfur and 0.5kg of sawdust are mixed. After mixing, they are ignited in several piles. After fumigation for one night, the residual bacteria in the shed can be killed.
3.3 Chemical control
Before the onset, 45% of chlorothalonil smog 300g can be used for fumigation for 8 hours at night for prevention. In the early stage of the disease, 10% difenoconazole water dispersible granules 1500 times solution, 40% flusilazole 7000 times solution, 50% phorhin WP 1000 times solution, 70% methyl thiophanate WP 1000 can be used. Double solution, 75% chlorothalonil WP 600 times solution, 10% Shigao 1500 times solution, 50% carbendazim WP 500 times solution, 50% benomyl WP 1000 times solution, 2% agriculture Anti-BO-10 water agent 200 times solution, 50% Krabi multi-wet powder 1500 times solution, 70% de Gaulle WP 1000 times solution, 40% DuPont Fuxing 800 times solution, 50% antibacterial WP 1000 times liquid, Kexing Dan 500 times liquid spray control, spray 1 time every 5~7d, even spray 3~5 times.
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