Introduction

This risk index uses weather data to estimate grape powdery mildew infection risk for each day. Categories of low, moderate, and high risk are assigned to index values. These categories can be used to adjust application intervals of fungicides or other management actions such as fungicide selection and intensity of scouting.

This app is a newer, streamlined interface for the existing model, which is also available through MyPest Page.

Using this App

Select the "Inputs" tab, search for weather stations near you, and choose one either from a list or a map. Be aware that some weather stations have poor quality or missing data. Our software estimates the quality of each station, but you may wish compare results for several nearby stations.

Optionally, you may choose a start date and a span (number) of days. If you leave the start date blank, the end of the output will be five days in the future, using forecast weather data, and the app will count back to a start date in the recent past. The weather forecast data is from the National Weather Service's "NDFD" forecasts.

Then, select "Graph" or "Table" to run the model. Your output will appear after 10-20 seconds depending on server load.

Interpreting the Results

Risk-index values (0-100) are categorized into low, moderate, and high risk. These categories can be used to adjust application intervals of fungicides or other management actions such as fungicide selection and intensity of scouting.

This app implements the Gubler Thomas powdery mildew model for the conidial stage of the Grape powdery mildew pathogen. It does not implement the ascospore stage. It also does not handle a reset of the index to zero after treatment.

For a detailed explanation of the model and risk categories, please see the UCIPM Extension page on powdery mildew. For general information about powdery mildew in grapes, see the Grape Powdery Mildew page from the Pacific Northwest Disease Management Handbook. For technical information about the Gubler-Thomas model, see our disease risk model documentation page.

Disclaimer: The index is intended to inform your decisions about management actions, such as choice and timing of control measures and intensity of scouting. It should supplement, not replace, the other factors you consider in making these decisions. Use at your own risk.

Email Subscription

Automated email delivery of the disease risk index outputs displayed in this app is available at no cost. An email subscription offers model results for this and several other plant disease models, for up to three weather stations, on a schedule that you select. To subscribe, you will need a uspest.org account.

Acknowledgements

• This app was funded in part by the USDA National Institute of Food and Agriculture, Crop Protection, and Pest Management, Extension Implementation Program (USDA-NIFA-CPPM-EIP).
• Dan Upper provided programming for the project.
• Location search uses data © OpenStreetMap contributors and data from MaxMind.