Something is eating it. Start reading up the bugs and pests related threads to get an idea what.
Diatomaceous earth if you want to be organic. Sevin powder if not, to pretty much cure what ails. Hardware store, pest control shelves.
Or live with it, fertilize, and watch in awe, while the bine pretty much grows faster than the bugs can eat it. Provided they don't cut it off at ground level, anyways.