Until we have enough funding we have to limit the number of queries per day. If you want to contribute please buy credits, subscribe, or donate. Subscriptions include automatic notifications of next spray dates, ascospore initiation, growing dergree days (by hour), recorded spray dates and other info. Thanks!
This a beta version. Future versions might have Downey Mildew, apple and other fruit tree risk tools. If you have a suggestion for future developement, please use the 'contact us' link at the bottom of the page.

Fine tune the temperature for your site

If the temperature at your site is warmer or cooler than data provided from the nearby weather stations, you may enter a temperature compensation here.
This will affect all data including threat indices and growing degree days.

Yesterdays Max: Min: Average:

Vineyard Manager

Vineyard Journal
Spray History
Water-Depth Data-Logger Visualizer

Your records show your last spray date was: (edit)

48N -123E

Or enter your city/town name and province/state [USA or Canada]:

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Powdery Mildew Management Calculator for Grapevines



We are collecting data on the growing degree days, fruit maturation, and weather data as it correlates to vine health, disease threat, and optimum fruit quality and yield. Please consider sharing your 'Vine Status' data with us (use the Vineyard Journal, and select 'Record Event'). We hope to contribute some valuable tools to our subscribers.
(* all data is completely confidential and will not be shared with our scientists without your express consent).

Growing Degree Days


Select a cultivar to display budburst, cap-fall, veraison (purple), and ripening (red) data on GDD chart

Accumulated Precipitation


Accumulated Solar Energy (MJ /m2 )

Thank you! Your contribution helps keep this site up and running

Chart 1: Model developer and citation: R. L. Snyder, La Vine, P. D., Sall, M. A., Wrysinski, J. E., and Schick, F. J. Grape Mildew Control in the Central Valley of California Using the Powdery Mildew Index. U. C. Cooperative Extension Leaflet 21342 (April, 1983).
This model calculates risk based on temperatures of 20-35 C for more than six hours and integrates precipitation and extreme temperatures.
Chart 2: (Available to subscribers) Model developer and citation: Thomas, C. S., Gubler, W. D., and Leavitt, G. 1994. Field testing of a powdery mildew disease forecast model on grapes in California. Phytopathology 84:1070 (abstr.). Weber E., Gubler, D., and Derr, A. Powdery mildew controlled with fewer fungicide applications. Practical Winery & Vineyard, January/February 1996.
This model considers leaf wetness, relative humidty as well as optimal growing conditions for the fungus.
University of California Integrated Pest Management:Powdery Mildew
Note: Future dates are predictions (for more accurate spraying times consult this calulator 5-7 days before your next planned spraying).
Temperatures are based on weather stations near you that are reliable, but predictions might be wrong, and your vineyard conditions may vary.
High humidity, low precipitation, cloudy skys, temperatures between 20-30C favor the fungus.

Note: Before using a model that was not field tested or validated for a specific location, a model should be tested for one or more seasons under local conditions to verify that it will work in the desired location.
The most critical time to manage fruit infection with fungicides is immediately before bloom through two to four weeks after bloom.
Conidial spore production occurs 7 to 10 days after primary infection by ascospores in early spring.
Kumulus DF (wettable sulfur): Table grapes - Do not apply later than 1 day before harvest. Wine grapes - Do not apply later than 21 days before harvest.

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