Combating Downy and Powdery Mildew in Portuguese Vineyards

Quality‑conscious wine producers in Portugal use a combination of traditional vineyard practices and modern tools to manage downy mildew (Plasmopara viticola) and powdery mildew (Erysiphe necator) – two common fungal diseases in grapevines that thrive in humid conditions and can seriously reduce both yield and grape quality.

Key strategies against downy and powdery mildew

1. Vineyard design and canopy management: Good vineyard design is the first line of defence. Producers choose well‑drained sites, orient rows to maximise sunlight and air flow, and use training systems that keep grape clusters as dry as possible. Pruning and careful canopy management reduce shading and humidity around the bunches, creating a microclimate that is less favourable for disease development.

2. Varieties and rootstocks with lower susceptibility: While fully resistant grape varieties are still rare, some growers experiment with varieties and rootstocks that show lower susceptibility to downy and powdery mildew. This can reduce infection pressure and limit the need for chemical treatments.

3. Monitoring and forecasting: Regular monitoring of the vines, combined with weather data and disease‑forecast models, helps producers predict when infection risk is highest. By knowing these critical periods, they can time their interventions more precisely and avoid unnecessary sprays.

4. Cultural practices and soil management: Cultural practices such as cover crops, controlled vigour and good soil management improve biodiversity and vine health. Strong, well‑balanced vines are generally more resilient and better able to cope with disease pressure, including downy and powdery mildew.

5. Biological Control: The use of biological control agents – beneficial fungi and bacteria that inhibit disease organisms – is growing. These products can form an important part of an integrated pest management (IPM) strategy and help reduce dependence on synthetic fungicides.

6. Fungicides used in a targeted way: When needed, fungicides remain an important tool. Quality‑conscious producers aim for targeted, well‑timed applications rather than routine spraying. They focus on the key risk periods identified through monitoring and forecasting, and they rotate fungicide groups to slow down the development of resistance.

7. Integrated Pest Management (IPM): IPM combines several methods into a single, long‑term strategy: choice of site and varieties, canopy and soil management, monitoring, biological control and, when necessary, chemical treatments as a last resort. The goal is to keep disease at manageable levels while minimising environmental impact.

8. Organic and biodynamic approaches: Some producers work according to organic or biodynamic principles, using only approved natural products and placing even greater emphasis on prevention through vineyard design and vine health. These approaches are often part of a broader focus on sustainability and environmental stewardship.

9. Innovative Natural Treatments: Many Portuguese winegrowers, especially those working organically or biodynamically, also experiment with non‑synthetic products against downy and powdery mildew. Examples include kaolin clay films that form a physical barrier on the leaf surface, orange oil and other essential oils, milk or whey sprays, potassium bicarbonate solutions and herbal teas such as horsetail (Equisetum). These products rarely replace fungicides completely under high disease pressure, but they can reduce infection levels, strengthen the vines and help lower overall copper and synthetic fungicide use when they are integrated into an IPM strategy together with good canopy management and monitoring.

By combining these measures, many Portuguese winegrowers manage downy and powdery mildew effectively and sustainably, helping to secure healthy grapes and wines that reflect their regions and grape varieties.

If you want to explore the science in more depth, a recent open‑access scientific review of grape downy mildew and its control strategies is available in the journal Microorganisms.