The reason farmers spray water before a freeze is because the water produces latent heat when it freezes.
As a result the sprayed water on the surface of the plant will then be converted to ice, and the heat trapped in it will then insulate the plant from the cold environment.
Spraying a plant with water in a colder region helps protect the plant from destruction because of the formation of ice on its surface.
This is because the heat released (exothermic reaction) during the solidification process is taken up by the plant, which therefore protects the plant from the freezing temperature.
In order to save the crop on such cold nights, farmers fill their fields with water because water has high specific heat capacity, so it does not allow the temperature in the surrounding area of plants to fall up to 0oC.
Some crop farmers store their crops on-farm, and spend winter shipping grain from their farm to ethanol plants, feed mills, and river terminals, where grain gets loaded onto barges and shipped far and wide.
Many farmers work on farm equipment like tractors and planters in preparation for spring tillage and planting.