- Downy mildew is one of the most serious fungal diseases affecting agricultural crops in humid and temperate regions. It is characterized by the appearance of pale yellow spots on the upper surface of leaves, accompanied by a white or gray downy growth on the lower surface.
- This disease not only damages the leaves, but also leads to impaired photosynthesis, premature leaf drop, decreased productivity, and sometimes complete crop destruction if preventive and therapeutic measures are not taken in a timely manner.
Symptoms of infection
- 🌱 Pale yellow spots on the leaves, later turning into dry brown spots.
- 🍂 A white or gray downy growth is evident on the underside of leaves, especially in the early morning.
- 🍇 In grapes: Early leaf and young bunch fall with poor growth.
- 🧅 In onions: Watery spots that quickly turn into dry, dead areas.
- 🥒 In cucumbers and zucchini: dry leaves and reduced fruit size and quality.
Most affected crops
- 🍇 Grapes.
- 🧅 Onions and garlic.
- 🥒 Cucumber and zucchini.
- 🌻 Sunflowers.
- 🌹 Ornamental plants.
Fungal life cycle
- The fungus overwinters in plant debris or soil as spores and sclerotia.
- When high humidity and moderate temperatures (15–25°C) are available, spores begin to germinate and establish the primary infection.
- The infection spreads rapidly by wind, rain, and sprinkler irrigation.
- The infection cycle can be repeated several times during the growing season, increasing the severity of the disease.
Economic damages
- Direct crop losses may reach 100% in severe cases.
- Low fruit quality and poor suitability for marketing and storage.
- Premature leaf fall hinders photosynthesis.
- Increased production costs due to the need for repeated preventive and curative spraying.
Prevention methods
- 🌿 Remove and burn infected plant remains after harvest.
- 💧 Avoid spraying as much as possible to reduce leaf moisture.
- 🌬️ Improving ventilation between plants, especially in greenhouses.
- 🔄 Follow a crop rotation and do not plant the same crop in the same land for consecutive years.
- 📅 Periodic inspection of plants to detect infection early.
Active ingredients to combat downy mildew
- Mancozeb.
- Copper oxychloride.
- Azoxystrobin.
- Metalaxyl.
- Fosetyl-Aluminium.
- 🕐 Spraying begins when the first symptoms appear, and is repeated every 10–14 days depending on the severity of the infestation and weather conditions.
Practical tips for farmers
- Don't wait for the disease to spread, start combating it as soon as the first symptoms appear.
- Focus on the underside of the leaves when spraying, as this is the center of infection.
- Alternate between different active ingredients to reduce the possibility of resistance.
- Integrated pest management (preventive + chemical) gives the best results in crop protection.