1. General Model Information
Name: powdery mildew disease forecast model for grapes
Main medium: terrestrial
Main subject: agriculture
Organization level: Population
Type of model: not specified
Main application: decision support/expert system
Keywords: grape, Powdery mildew, Uncinula necator, forecast, phenology, degree-day
Department of Plant Pathology, University of California, Davis.
Thomas, C.S., Gubler, W.D. and Leavitt, G.
Model Description: This model contains two stages based on pathogen biology, an ascospore
and a conidial stage. Check with your local Cooperative Extension agent to determine if both
stages are important in your area.
Ascospore stage. To determine ascospore infection risk levels, the model calculates the daily
average temperature and measures the hours of leaf wetness. The model modifies the Mills table
developed for apple scab ascospore infection by predicting infection based on 2/3 of the hours of
required wetness .
Model Validation: Since 1995 validation work has been conducted in multiple growing regions of
California. In 1997, California PestCast is sponsoring validation projects in additional table and
wine grape areas and in raisin grapes. The model is also being validated in New York,
Washington, and Oregon; Germany, Austria, and Australia.
Model Implementation: This model is being implemented by University of California Extension
Plant Pathologist Doug Gubler, growers, Cooperative Extension advisors, and licensed
consultants in several grape-growing counties in California. Disease risk indices for many
California weather stations are available on a WWW site in the Department of Plant Pathology,
University of California, Davis.
II. Technical Information
III. Mathematical Information
Plant phenology, pathogen phenology
Environmental: Hourly average temperature, daily maximum temperature, hourly leaf wetnessduration.
Calculated: Daily average temperature; daily value of number of hours that 70<=T<=85 F.
Thomas, C.S., Gubler, W.D. and Leavitt, G. 1994. Field testingof a powdery mildew disease forecast model on grapes in California. Phytopathology 84:1070(abstr.).
Weber E., Gubler, D. and Derr, A. 1996 Powdery Mildew Controlled with Fewer FungicideApplications Practical Winery & Vineyard January/February 1996.
V. Further information in the World-Wide-Web
VI. Additional remarks
Information and remarks about the application of this model
Last review of this document by: T.Gabele 19.08.1997
Status of the document:
last modified by
Tobias Gabele Wed Aug 21 21:44:44 CEST 2002