What weather conditions increase powdery mildew risk?

Powdery mildew (Erysiphe necator) thrives in warm, dry conditions with moderate humidity. Optimal conditions are temperatures between 70-85F (21-29C), humidity above 40%, and diffuse light. Unlike many other fungal diseases, powdery mildew does NOT require free water for infection, making it a persistent threat throughout the growing season.

How does leaf wetness duration affect disease?

Leaf wetness duration is critical for downy mildew and botrytis infection. Downy mildew (Plasmopara viticola) requires free water on leaves for spore germination, with infection risk increasing significantly after 4+ hours of wetness. Botrytis typically requires 15+ hours of wetness at moderate temperatures for infection.

Should I spray based on this risk assessment?

This tool provides general risk guidance based on environmental conditions. Always consult with a licensed Pest Control Advisor (PCA) or agricultural extension specialist before making spray decisions. Consider your specific varieties, spray history, growth stage, and local conditions. This tool does not replace professional IPM advice.

What is the difference between disease risk and disease pressure?

Disease risk refers to the likelihood of new infections based on current environmental conditions. Disease pressure refers to the actual amount of inoculum (pathogen) present in the vineyard from existing infections. A block can have high risk (favorable weather) but low pressure (no nearby inoculum), or vice versa.

Vineyard Disease Risk Assessment Tool

The Disease Risk Assessment Tool evaluates the risk level for common vineyard diseases based on environmental conditions you provide. Enter temperature, humidity, rainfall, leaf wetness duration, and canopy density. The tool calculates risk scores for powdery mildew, downy mildew, and botrytis using established epidemiological models. Results include risk level ratings and suggested management actions.

Environmental Conditions

Temperature (°F)

Relative Humidity (%)

Rainfall Last 48h (inches)

Leaf Wetness Duration (hours)

Canopy Density

Enter weather conditions to assess disease risk

Important Safety Disclaimer

This tool is for informational and planning purposes only. Always read and follow the complete product label before any pesticide application. The label is a legal document and takes precedence over any calculator output. Consult a licensed Pest Control Advisor (PCA) for site-specific recommendations. VitiScribe is not responsible for decisions made based on this tool.

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