This microorganism causes a disease of lettuce (Lactuca sativa) denominated as downy mildew.

Experiments using sporangia from hosts do not infect lettuce and it is concluded that the fungus exists as a quantity of host-specific strains (formae speciales).

The severity of damage caused by Bremia can vary depending on environmental conditions.

High humidity and cool temperatures are optimal for infection and spread of the disease.

Other practices include removing infected plant debris from soil and application of fungicide.