In Our Field:High temperatures, wet soils cause crop losses

July 05, 2001|By THOMAS TURINI

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.


The higher the temperatures, the shorter the time necessary for flooding to cause damage. At soil temperatures of 95 degrees, injury can occur after the field is flooded for 30 hours. When soil temperatures are 100 degrees, plant death can occur when the soil is saturated for 24 hours. At soil temperatures above 104 degrees plants can be killed when soils are waterlogged for much shorter periods.

The more recently the alfalfa was cut, the more susceptible it is to high-temperature flood injury. It is suspected this is because the leaves are capable of taking in and supplying the roots with some oxygen. Recently mowed plants should not be irrigated while temperatures are high.

In addition, flooding for short periods (about four hours) when temperatures are high reduces chances of injury. Some soils remain saturated for a long period following irrigation because of the soil type, the slope of the land and the length of the run, so field selection and soil preparation before planting is important.

In addition, when temperatures are high and soils are wet, a bacterial disease can severely damage sugar beets. The bacterial species, Erwinia caratovera, causes a root rot under these conditions. This type of bacteria is common in agricultural soils; however, when the soil is well drained and temperatures are cool, the bacteria will not damage the roots. In late season sugar beets, a long irrigation or a poorly drained field will create conditions favoring development of this disease and can result in complete crop loss.

As with scald, the chance of the occurrence of bacterial rot of sugar beets is reduced by careful irrigation management.

Imperial Valley Press Online Articles