Diseases occur when environmental conditions (weather, management, and/or site conditions) become favorable for the buildup of pathogen populations and/or cause an increase in the susceptibility of the plant.When this happens, turfgrass loss can occur.

There are a group of turfgrass diseases for nearly every environmental condition that may arise. Some diseases develop during the frigid months of winter under a blanket of snow, whereas others occur only during the hottest and most humid conditions of summer. Some diseases appear more frequently in wet soils and following applications of high rates of fertilizer, while others are triggered by drought and low fertility.

Three factors are required for a disease to develop: a susceptible plant, a pathogen, and an environment that is favorable for pathogen growth. Disease will not develop unless all of these factors are present for at least several consecutive days. Because turfgrasses are perennial, the host plant is always present. The pathogens are always present as well, laying dormant in the thatch and soil when they are not causing disease. Therefore, it is the environment that triggers disease development. Weather conditions, management practices, and microclimate are the environmental variables that have the greatest impact on disease development.