The Gubler Thomas Model for Grape Vine Powdery Mildew Risk

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Powdery Mildew in Canope Graphical Presentation of the Gubler Thomas Model

The spread out of Uncinula necator during the summer (when conidia are produced) is influenced primarily by temperature. The optimal temperatures for the Powdery Mildew are between 21°C and 32°C. The greater the number of hours daily that the temperature is within this range, the higher is the risk for Powdery Mildew. Days with more than 6 hours of temperature in this range increase the risk about 20 points. Days where the temperature is not within this optimal range reduces the risk about 10 points. These are days with temperatures under 21°C the whole day long or days where the temperature exceeds 32°C for 6 hours. If the Powdery Mildew risk is less than 20 points spraying interval can be extended. With 20 to 60 points the normal spraying interval is valid. If the risk is more than 60 points you should shorten the spraying interval. 

  • Risk increases: With every day with equal or more than 6 hours of 21°C <= Temperature < 32°C ==> +20 Points
  • Risk decreases: With every day when temperature is 32°C or above or when 6 hours of at least 21°C are not reached ==> -10 Points

(in FieldClimate.com it is called : The Powdery mildew California risk)

The PM CA- Gubler model in strawberry has the same conditions for infection (just other temperature thresholds).

(c) Dr. Heinrich Denzer, Pessl Instruments GmbH, Weiz, 2008 


Created by system. Last Modification: Thursday 26 of March, 2015 07:54:10 GMT by cpilz.