I dont think there is an exact temperature at which you should stop - but as the fish become less active, you should feed less and less, as they are using up less and less energy. I think you can get winter food now which you can feed throughout winter months...but Ive never tried any myself - and I stop feeding from near the start of december I think until into febuary. And the fish are always fine afterwards. Alot of people turn pumps of over winter - certainly have it off when/if the pond freezes over - but keep it on as much as you can. You can also get pond heaters - which keep an area of ice on the surface open, but again I leave my ponds to just freeze over. Never crack the ice on top.
Hope this helps.
Thom.