Maintaining a healthy, vigorously growing lawn is the best way to prevent a severe disease outbreak in a turfgrass. A 5,000 square foot lawn contains about four million turfgrass plants, each requiring optimum amounts of water and fertilizer, the right mowing regime, and an aerated, well-drained soil.
About 75% — 85% of common lawn diseases can be avoided altogether just by optimizing these practices to avoid stressed grass, which is much more susceptible to disease outbreaks than healthy grass.
For a disease to occur, all three sides of the "disease triangle" must be present. Even if a disease-causing pathogen is present, infection will not occur unless the environment (temperature, quantity of water, etc.) is conducive to disease development and a susceptible host (species of grass) is available.
Homeowners can prevent major disease infestations from occurring by planting locally adapted lawn grasses and providing good care. Selecting species adapted to the climate and intended use and following through with cultural practices that favor the grass rather than the pathogen are important steps a home gardener can take to avoid severe lawn diseases.
Many diseases reduce the quality of the lawn for only a short time and do not result in adverse long-term impacts. Often, when the weather becomes more favorable to growth of the turfgrass, the lawn will recover on its own if proper cultural practices are maintained. Few, if any, fungicide applications should be necessary under these conditions.
It is important to follow sound watering practices (whether hand-watering or using some type of automated system) to promote an environment favoring lawn growth rather than a disease outbreak.
Too much or not enough water results in unhealthy, slow-growing grass vulnerable to disease causing organisms. Waterlogged soils are poorly aerated, restricting root growth, that promotes diseases. It also allows algae and moss to thrive.
In general, a deeply watered lawn develops a deeper and extensive vertical root system, providing it with greater drought and disease resistance than a shallow-watered lawn.
Warm-season turfgrasses (bermudagrass, zoysiagrass, and St. Augustinegrass) are more drought resistant than cool-season grasses (tall fescue, perennial ryegrass, Kentucky bluegrass) and require about 20% less water.
It is best to water the lawn until runoff just begins, and avoid watering each day. The number of times to water each week depends on how long the irrigation system can run before water just starts to puddle or run off the soil surface laterally. For example, if a grass needs 40 minutes of irrigation each week, but runoff begins after 20 minutes, then water twice a week for 20 minutes.
In cases where soil takes up water so slowly that runoff occurs before 10 minutes, water cycling is necessary. To cycle, irrigate until runoff just begins, turn the system off, and repeat the process in 30 minutes before the soil surface dries out. Several cycles per day may be necessary to apply the desired amount of water.
The best time to water is early in the morning, when evaporation rates are lowest and water pressure is at its peak. Irrigating in the afternoon is wasteful because of higher evaporation rates, and prolonged damp conditions in the evening may encourage disease development.
Irrigation requirements change from month to month and may not be needed at all if it has rained. Reset your sprinkler system to meet your lawn's changing irrigation needs.