I have to say, one of my best field-edge tree stands is in a group of Ailanthus ("tree of heaven")!! But other than that, I agree that its a useless and prolific invasive species. Since they're either dormant or headed that way now, I'd hold off on doing anything with them at this time. In the Spring, when they start pushing, do a circumferential basal spraying of the trunk with the herbicide, Pathfinder-II. I don't think its Restricted. I've used it and it works very well for permanent removal of Ailanthus.
I know grasses/weeds are storing nutrients in roots this time of year but not sure if that holds true for trees or not. Anyway, I found a Penn State fact sheet addressing Ailanthus. They say the timing for basal spraying is critical and best done is between mid-June to mid-September. Here's the link if anyone's interested: http://vm.cas.psu.edu/Publications/FS_3_AILAL_v2.pdf