Easy solution, dig out those B58 9 megaton gravity (laydown fused) bombs and apply liberally to the affected area. Repeat as neccessary.
Fallout? Yep. OVER THEIR SOIL.... War is hell
Nice thing about nukes in the megaton range is they blow the fallout up so high into the atmosphere, by the time it comes down its cooled off quite a bit.
That would be B53, not B58....sorry. The old Titan 2 warhead, BTW.