Wonderful article cutworm!
I moved it up to the trading forum for you.
i have used irrigation to protect my citrus trees several times. here is what i do. if i know it is going to be about 30 degrees overnight, i will just run some water thru a hose. the tree has a slight well (so the water stays around the tree about 6 inches deep. the water coming out of the ground is about 55 degrees. so the warmth of the water rises and keeps the tree from freezing. here in the tucson area, it rarely gets much colder than that.
if i think it will get down to about 20, then i put a couple large candles under the tree. some people use a flood lamp. a candle or a flood lamp puts out enough heat to prevent frost damage. (if you only have a couple trees to protect).
it is only a problem for people down in the low spots. cold air sinks. if you are half way up a slope, then this is less of a problem.
i may have to do this 12 or 15 times each winter.