We are covered in these guys and dont get me wrong as i like a nice block of Ash in the stove but it will be great to see em slow down.. http://www.thewhig.com/2014/01/07/extreme-cold-could-kill-emerald-ash-borer-researcher
How cold is -30 C ? I think once all the ash is dead, the borer will die, and the trees can grow back.
I took alot of Ash down this year because of them and i bet there will be a whole whack coming down next year also.. I'm pushing 50 years and still gotta google this friggen metric firecracker -30ºC = -22.0ºF