Turfgrass Temperature Stress, Part 2: Water

In a previous post I discussed the optimum temperatures for the growth of turfgrasses (Turfgrass Temperature Stress, Part 1: Optimal Temperatures).  In that post I mentioned that if there is water available to the plant, it is rare heat stress occurs.  This is where a balancing act is need when managing turf in hot temperatures.  Water has several unique properties that can help or hinder what we are trying to accomplish on the course.

Turfgrass uses a process called transpiration to cool itself, just like we use perspiration to cool ourselves.  The turf draws water from the roots up to the leaf surface to evaporate.  The moisture draws heat from the leaf surface and surrounding air to complete the process of evaporation.  This causes the leaf surface to cool. If there is water available for the plant to complete this process, it has the ability to continually cool itself.  A few factors may limit this process.  If portions of the root mass of the plant have died as a result of excessive soil temperatures, there will be fewer roots available to pull water from the soil and move it to the leaf surface. This will require much more frequent watering to keep enough moisture in the upper zone of the soil, and available for the plant.  Another factor that may limit this process is the humidity of the air.  The more moisture there is in the air, the less the moisture will be evaporated from the leaf surface, preventing the plants ability to cool itself properly.

The presence of moisture is also a catalyst for the development of diseases in turf.  Excessive soil or leaf wetness can lead to the development of diseases.  When the plant is weakest during the summer months, it is also most vulnerable to pathogen infestations.

The summer heat on cool-season turfgrasses can be quite a balancing act.  Providing enough moisture for the plant to cool itself, but at the same time preventing excessive moisture that may cause the development of diseases.  This requires a well calibrated irrigation system coupled with diligent hand watering.
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