The disease has been observed in Europe and parts of Asia, and on wild hemp in Illinois, suggesting that it has spread to the Western hemisphere.

[2] Downy mildew of hemp requires cool, moist weather in order to produce spores.

The sporangia pop open to release the zoospores, which require water in order to swim and infect a plant.

At the end of the growing season, the pathogen overwinters by oospores that can be found in the soil or on plant debris.

Also, simple practices such as a shoe washing station at the entrance of every greenhouse can help minimize the risk of spreading the disease to multiple growing areas.

This process heats the soil to very high temperatures, with intentions to destroy the overwintering oospores which would otherwise restart the disease cycle in the spring.