DESCRIPTION: The pathogen (Peronospora
belbahrii) is a water-mold (oomycete) that can be
spread by contaminated seed, by infected basil
leaves, and as wind-dispersed spores. Spores of
the pathogen are capable of being dispersed long
distances. Infected basil leaves produce an
abundance of spores. Thus the pathogen can
spread widely once introduced to an area. The
optimum environmental conditions for disease
development occur at high humidity levels with
extended periods of leaf wetness.