In most cases, it definitely pays to irrigate. If Florida had soils with better water holding capacity and if rainfall came when the trees needed it, then irrigation would not be necessary except for frost protection. But periodic droughts and coarse-textured soils have convinced most growers that irrigation is worthwhile. Water stress can be caused by many factors, but the simplest cause of water stress is that water loss from the plant is greater than water uptake. Hot dry winds can desiccate trees by removing water from the leaves faster than they can take water up.
Cold soil can promote wilting by slowing root water uptake.
Ironically, flooding can also cause wilting. The excess standing water can damage roots and thus reduce water uptake, particularly if toxic hydrogen sulfide builds up in the soil. Usually, wilting is caused by inadequate water. When the soil is dried to the point where the tree cannot recover from a wilt by the next morning, the soil is said to be at the permanent wilting point. Growth, or cell enlargement, is the process that is most sensitive to water stress.