Guidance on Prevention and Control of Greenhouse Cucumber Downy Mildew During Peak Damage Period in Liangzhou District
Greenhouse vegetable cultivation is a competitive industry in Liangzhou District, with cucumber as the primary winter crop in towns including Dam, Shuida, Fenbu, Qingyuan, and Sidam. Since late October, cucumber downy mildew—a fulminant and highly destructive disease—has entered its peak damage period. Notably, some newly established greenhouse farmers have faced outbreaks due to inadequate temperature and humidity control, leading to excessive nighttime humidity, severe leaf dew, and subsequent disease occurrence. In response to key issues in current disease management, Gan Guofu, a researcher from the Agricultural Technology Promotion Center, recommends the following pharmaceutical prevention and treatment techniques, along with supporting management measures:
1. Proactive Pharmaceutical Prevention for Non-Infected Greenhouses
For greenhouses without downy mildew symptoms, implement proactive prevention as follows:
- **Initial application**: Add 1 bag (25g) of 70% Antai Sheng WP and 12.5ml (1 bottle) of 68.75% Silver Farley Suspension to 15kg of spray water. Spray evenly on both the front and back of cucumber leaves.
- **Subsequent maintenance**: After the initial spray, apply 25g of 70% Antai Sheng WP per 15kg of water every 7 days for 4–5 consecutive sprays. This measure achieves disease prevention, zinc supplementation, and leaf retention effects.
2. Targeted Treatment for Infected Greenhouses
Downy mildew spreads rapidly. Once diseased leaves or focal infection areas are detected:
- Immediately remove and dispose of diseased leaves to prevent further spread.
- **Emergency treatment**: Add 25ml (2 bottles) of 68.75% Silver Farley Suspension and 1 bag (25g) of 70% Antai Sheng WP to 15kg of spray water. Spray evenly on both sides of leaves.
- **Effect assessment**: Judge effectiveness by observing lesion changes:
- Effective: Lesions turn brown, edges are neat and dry, and surrounding leaves remain bright green.
- Ineffective: Lesions retain mold layers, surrounding areas stay yellow-green, and spread continues. In this case, reapply the treatment within 5–7 days based on disease progression.
3. Humidity Control to Suppress Disease Occurrence
Cucumber downy mildew thrives in high humidity, low temperature, and poor ventilation. Spores germinate and infect leaves when nighttime temperatures drop from 20°C to 12°C and leaf water films persist for ≥6 hours; the disease cannot develop without leaf water films, even under favorable temperatures. When relative humidity reaches ≥83% (accompanied by leaf water films), the disease is likely to occur. Key humidity control measures:
- Cover ditches with plastic film to reduce soil moisture evaporation and air humidity.
- Irrigate shallowly in ditches on sunny mornings; avoid irrigation on rainy/snowy days or flood irrigation. Ventilate promptly after irrigation to reduce humidity and prevent leaf dew.
- Conduct short-term early-morning ventilation to replace humid air, rapidly raise temperatures, and eliminate excess moisture.
4. Optimization of Spraying Operations
To improve prevention and treatment efficacy:
- Use dedicated greenhouse sprayers, preferably with copper nozzles and small spray holes to produce fine droplets.
- Ensure sufficient spray pressure for even distribution of droplets on both sides of leaves (tilt nozzles upward to cover leaf undersides).
This guidance is intended to help farmers standardize disease management practices and minimize losses from cucumber downy mildew.
