There have been several attempts to combine host and pathogen development since in order to account for the effect of changing environments on disease progress. According to Hau (1990), the only way for a disease progress curve to diminish is through a changing host, either by (i) an increase of susceptible tissue, referred to as a dilution effect, or (ii) by the loss of the diseased tissue by defoliation, referred to as a thinning-out effect, or (iii) as
a result of ontogenic resistance. For vine and powdery mildew, a set of deterministic models taking into account host growth and based on the modified Van der Plank equations were developed (Sall, 1980; Blaise & Gessler,1992; Gessler & Blaise, 1992).