Turf disease development is strongly influenced by environmental conditions within the turf canopy and the soil around the root zone. Temperature plays a role of course; for instance, red thread is typically seen in cooler weather, while brown patch appears in the heat of the summer. Free moisture and humidity also play a key role in promoting disease. Most fungi that cause plant diseases require free moisture to be available on plant surfaces for a certain amount of time for spore germination and infection to occur, and high humidity further promotes disease development.
While we can’t do anything about the weather, there are things that turf professionals can do to decrease humidity and free moisture in the turf microclimate and make conditions less hospitable to pathogenic fungi. This involves active effort to keep leaf wetness periods as short as possible, and facilitating rapid drying of foliage after rain or irrigation. This can be accomplished by increasing air circulation and sun exposure on the turf; factors that are best considered prior to turf establishment but may be improved for existing sites by strategically pruning or removing trees and shrubs. Examples of more targeted practices include dragging a hose over turf in the early morning to speed drying by knocking dew off the leaf blades.
Watering is best done in the early morning, as increasing temperatures and sunlight will promote rapid drying of foliage as the day progresses. To maintain growth during summer, a general guideline for lawns in Southern New England is one inch of moisture input per week from either precipitation, supplemental irrigation, or a combination thereof. Watering deeply and infrequently is the best way to manage soil moisture in lawns. This practice also promotes the development of deep roots, an important characteristic that makes turf less susceptible to environmental stress and diseases. Excessively wet soil is not only conducive to numerous diseases, but the exclusion of oxygen in waterlogged soil also impairs proper root function, weakening turf and making it more susceptible to pathogens.
Submitted by: Dr. Angela Madeiras