Cucumber downy mildew, caused by the pathogen *Pseudoperonospora cubensis*, is one of the most devastating diseases affecting cucumber crops in protected cultivation. In conventional farming practices, farmers often rely heavily on repeated applications of chemical pesticides to manage the disease. While this approach can provide some level of control, it comes with significant drawbacks, such as high pesticide residues that may pose health risks to consumers. Moreover, the continuous use of chemicals has led to increasing resistance in the pathogen, making it harder to manage the disease effectively over time. To address these challenges, we have developed a series of eco-friendly and sustainable methods for controlling cucumber downy mildew.
One of the most cost-effective and environmentally friendly strategies is to use resistant cucumber varieties. Several cultivars have been proven to be highly resistant to downy mildew, including Zhongnong No. 7, Zhongnong No. 12, Jinchun No. 3, and Jinza No. 2. By planting these varieties, farmers can significantly reduce the need for chemical interventions while maintaining good crop yields.
Ecological control plays a crucial role in managing the disease without the use of chemicals. This method involves adjusting environmental conditions to create an unfavorable environment for the pathogen. Cucumber downy mildew thrives in temperatures between 16-24°C and relative humidity above 85%. When temperatures drop below 15°C or rise above 30°C, the disease is suppressed. Similarly, when air humidity falls below 50-60%, the pathogen cannot produce spores. Based on these principles, several practical measures can be implemented:
In the morning, ventilate the greenhouse for 30 minutes to 1 hour to remove moisture, then close it to maintain warmth. Raise the temperature to 28-30°C (not exceeding 35°C) to promote plant growth and inhibit the disease. In the afternoon, lower the temperature to 20-25°C and reduce humidity to 60-70%. Close the greenhouse when the temperature drops below 18°C. In the evening, ventilate again for 2-3 hours. If nighttime temperatures remain above 12°C, it’s safe to leave the vents open overnight. On cloudy or rainy days, proper ventilation and moisture management are still essential.
Good agricultural practices also contribute to effective disease control. For instance, using drip-free film helps reduce humidity and improve light transmission, which supports healthy plant growth and reduces disease pressure. Full coverage of mulch film increases soil temperature, promotes root development, and lowers air humidity, further reducing the risk of infection. Under-film irrigation during winter should be limited, avoiding flooding. Watering should be done in small amounts under the film during sunny days only. After watering, close the greenhouse and raise the temperature to around 35°C for an hour before ventilating to remove excess moisture.
When necessary, chemical control can be used with low-toxicity, low-residue pesticides. It is strictly forbidden to use highly toxic or long-residue products. Recommended options include 74% chlorothalonil wettable powder diluted 600-800 times, 58% thiram-Mn-Zn wettable powder at 500 times, 72% Kexin wettable powder diluted 600-750 times, and 72% Azoxystrobin emulsifiable concentrate diluted 800-1000 times. These products should be alternated to prevent the development of resistance in the pathogen. Regular monitoring and timely application are key to achieving effective disease control.
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