Under extreme high temperature conditions – when the temperatures reach the upper 90’s and above – the grass plants will begin to shut down as a defense. In some cases such as with annual bluegrass they often die in a relatively short period time. One of the most important things you can do as a turf grass manager is to try and cool the turf. The best way I know is by a light application of water to create evaporation cooling. If you have an in ground irrigation system this means turning the system on to give you approximately .05” of water. You do not want to flood the turf at this time because you can create scald and cook the grass plants. The timing of this water application ( in this case called syringing) should be just before the hottest time in the afternoon. When I was a golf course superintendent we would begin this around 2 PM.