Maybe there are some farmers on the SD who can answer this: Reading an old book about life in the late 1800s, it is described that they had to drop scoops of water on (or around?) corn plants in a frosted cornfield to thaw the young corn plants before sunup. Otherwise, the sunlight would kill the crop. Can someone explain how this all worked?
I can see how the scoops of water may defrost a plant, but why would sunlight kill the unthawed plants?
I’ve read that the frost on plant leaves can form small lenses and will allow the suns rays to be concentrated to burn the leaves. I was told to use a hose to wash the frost off before sunrise. But thinking about it now, wouldn’t the drops left by the hose do the same thing?
Maybe they were dropping water on the plant rather than on the ground at the roots.
This link says to not wash off the frost but that watering the night before can moderate temperature.
http://aggie-horticulture.tamu.edu/archives/parsons/misc/coldprot.html
The cold kills by freezing the cells, the 10% increase in the volume of the water as it freezes damages the structure of individual cells…
Dawn is the coldest part of the day, so if the freezing conditions only occurred a few days a year, that would probably be just before dawn, and then you can save the plants by watering just before dawn … the water that is 15 above freezing is enough to warm the plant and prevent the plant freezing
That is, the only reason to water is to warm the plant up.
Was the book Laura Ingalls Wilder’s Farmer Boy? I remember that scene.
I’ve grown a bit of corn, I am surrounded by cornfields, and can’t think of any reason to do this. I guess it might warm up the plant. I can’t see how the sunlight would kill the plant.
In some orchards here and in Florida, they spray the trees with water, when a frost is predicted. More so in Florida.
Beat me to it Bubba. 
Water is sprayed in orchards when fruit is budding and frosts still occurring. The water freezes around the fruit and insulates from temperatures below Zero degrees Celcius (32 Fahrenheit).
It sounds counterintuitive but apparently it works.
It seems that the idea of the sun burning holes in leaves holding water droplets due to a prism effect is bunk (I have never seen it in all my years of gardening). And I suspect that ice crystals wouldn’t do it either.
Any burn related to frost should be from minute ice crystals formed within plant cells and not from exterior frost, or else Florida orange growers would lose their crops after spraying them with water during cold snaps.
I do as well. Puzzled me as a child.