Mature sporangia are dispersed via wind and release zoospores to infect leaves, cones, and shoots.

Mycelia grow systemically throughout the plant, leading to the infection of the crown and buds in which the pathogen will overwinter.

[3] A sexual stage also exists for P. humuli, in which an antheridium fertilizes an oogonium to produce a recombinant oospore.

While oospores are classically thought to be the chief survival structure of oomycetes, their role in primary infection in downy mildew of hops is uncertain.

Studies have found that hours of relative humidity >80%, degree-hours of wetness, and mean night temperature are paramount in predicting model plants' susceptibility to infection.

[2] The pathogen favors extended periods of wetness, high humidity, and mildly warm temperatures ranging from 15.5–21 °C (59.9–69.8 °F).