Plant pathology farm adviser,
UC-Imperial County Cooperative Extension
With the onset of high temperatures, careful irrigation management and good drainage are more important than ever to maintain good plant health. Substantial crop damage can result when soil temperatures are high and soils are saturated for long periods.
High-temperature flood injury, also called scald, commonly damages alfalfa, although the condition can affect many crops. The damage is not a direct affect of high temperature but is caused by the lack of oxygen in the root system. Plant roots need oxygen for biological processes. As temperatures increase, the rate at which these biological processes occur increases, so more oxygen is required and more is used. Soil inhabiting microbes will use more oxygen at high temperatures, so the soil becomes oxygen-deficient, quickly causing the roots to suffocate.
Five to 10 days following flood irrigation while temperatures are high, nearly all plants in a poorly drained or over-irrigated area may wilt and die. The leaves of affected plants wilt and fade to a light green. The inner tissues of the root system die and turn brown. Typically, there will be obvious patterns in affected fields. Plants will die in areas where water stood for a long period of time.