Cucumber scab is a devastating disease; how can it be controlled?

    Cucumber scab is a fungal disease and one of the devastating diseases of greenhouse cucumbers. Once it occurs, control must be carried out promptly; if control is not timely, economic losses can be great. Cucumber scab can occur at a relative humidity of about 90% and at temperatures of 9-30°C. The scab pathogen invades through the epidermis, stomata, and wounds of the cucumber. The presence of water droplets on the greenhouse film and on the cucumber leaves inside the greenhouse is an important condition for the occurrence of scab. When humidity inside the greenhouse is high, light is weak, and watering is followed by consecutive cloudy days, the disease is severe. In the greenhouse, the scab pathogen exists as mycelium and serves as the primary source of infection; conidia can also attach to the surface of cucumber seeds, or mycelium can lie dormant inside the seed coat, causing the cucumber seeds to carry the pathogen. Seed-borne infection can infect cucumber seedlings, and infected cucumber seedlings will develop the disease quickly after transplanting.

Cucumber scab

 
    Control methods:

    1. Choose cucumber varieties resistant to the disease.

    2. For cucumber seeds, soak them in warm water at 55-60°C for 15 minutes, or soak them in a 500-fold solution of 50% carbendazim wettable powder for 20 minutes, rinse them clean with water, and then germinate them.

    3. Strengthen management: when temperature is guaranteed, ventilate as much as possible to remove moisture, reduce leaf condensation, and inhibit the germination and invasion of the scab pathogen; in winter, water little but often, and do not flood-irrigate; frequently wipe the greenhouse film to increase light transmission.

    4. Use 45% chlorothalonil smoke agent at 300 g per mu to fumigate the greenhouse at night for about 8 hours.

    5. In the early stage of cucumber scab, foliar spraying can be used for control with a 1500-fold solution of 10% difenoconazole water-dispersible granules, a 7000-fold solution of 40% flusilazole, a 1500-fold solution of 12.5% myclobutanil emulsifiable concentrate, a 1000-fold solution of 62.25% myclobutanil · mancozeb wettable powder, etc., depending on the condition of the disease, at intervals of 5-7 times.