Just a thought, If it's just a hard frost and you have a few trees you can put a sprinkler on them overnight and turn it off when the morning sun melts the frost on the ground.
I'm in southern Wisconsin. ( Sounds like a oxymoron) but have 100+ apple tree orchard. Last two years we have had a late enough frost to kill the flowers/ovaries. I've only ever seen this 2 times in 40 years and it was the last two. Looks like it may be a 3rd in a row. Seriously considering cutting them down and turning it into pasture. What's the point of 100 trees to get a dozen apples. This global warming thing really sucks. :bang: