July brings heat… and humidity — the perfect storm for one of the most dangerous threats in the vineyard:
 Downy mildew, caused by Plasmopara viticola.

 Symptoms
• Leaves: translucent oil spots on the upper surface and white mold on the underside.
• Young shoots: can darken and collapse.
• Grape clusters: may shrivel, dry out, or rot → direct yield and quality loss.

 When does it strike?
The “Rule of the 3 Tens” can help predict when downy mildew is likely to appear. It considers the following conditions:
At least 10 mm of rain
Temperature above 10 °C
Shoots longer than 10 cm
When all three happen simultaneously, primary infections can occur.
If wet conditions continue, secondary infections can follow throughout the season.

 How to manage it
 Preventive treatments (copper or systemic, depending on growth stage)
 Canopy management to improve airflow
 Use of forecasting models (DSS) to optimize timing
 Frequent field scouting after rainfall

 Want to know more?
Thanks to the manual developed in the KICRO project, growers can learn not only about downy mildew, but also about many other grapevine diseases and how to prevent them.