FieldClimate.com displays the risk of Uncinula necator together with the climate conditions.
The risk is displayed in a line ranging in between 0 and 100%.
Do to the fact that only one risk value per day is calculated it is best to view this data aggregated on one day. If 100% are reached, conditions for an infection have been fullfilled.    

The risk of a Grape Vine Powdery Mildew infection depends on the inoculum already established in the vineyard. This restricts the use of the model. First decision which have to be made is what is the major source of inoculum: Is it flag shoot or is it ascospore. If flag shoots are present we have to control them independent of the risk figures. The risk model points out periods where climate is favourable for disease propagation. This will mostly be the fact from June to end of August. The model indicates very good years where disease can start more early or where disease will never be a big problem.

  Decision rule for the risk model:

less than 20 Points => prolongate spray interval (sulfor can be used)
20 to 60 Points => normal spray interval (use systemic mainly non DMI fungicide) more than 60 Points => shorter spray interval (use DMI fungicide with shorter spry interval)