Image      Graphical Presentation of the PI GVPM Risk Model

The spread out of Uncinula necator during the summer is influenced primarily by temperature. The antagonistic fungi Ampelomycees quisqualis is mainly favoured by free moisture. 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. Days with long leaf wetness periods are leading to the build up of A. quisqualis. A build up of this fungus will break an U. necator epedemy. 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 starts: with 3 days with equal or more than 6 hours of: 21°C <= Temperature < 32°C ==> 60 Points
  • 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 does not reach 21°C or every day with 6 hours of: 32°C <= Temperature and every day where leaf wetness is lasting longer than 8 hours (implementing A. quisqualis) ==> -10 Points

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