The grape-powdery mildew pathosystem is characterized
by a polycyclic pathogen capable of explosive multiplication
and a host population with a high degree of spatial
structure at the field level and with a complex architecture
of leaf and berry structure at the individual plant level
exhibiting rapid changes over time. As well as environmental
differences, the high degree of human interference
during vine development and the wide diversity of cropping
systems further enhances variability from one crop to
another and hence, variability between epidemics.