Why my Fallopia is death?

I'm amazed - this plant (known as mile a minute vine) usually grows rampantly and is very difficult to kill off if you want to get rid of it and there are no particular diseases which it suffers from, its very resilient. First, is it growing in the open ground or do you have it contained, either in a pot or something that restricts its roots? Restriction at the roots might cause plant collapse as the summer progresses. Second, this plant does much better with plenty of water available to it, so have you been giving it plenty often enough? Otherwise, I can't think of anything else that might cause this problem. Hope that helps.

It is in open ground and I use an automatic irrigation system (water drop type). Near by my Fallopia there is an Hydrangea that is still there, so I do not think it suffered for luck of water.
I am thinking to a disease or a parasite but without any evident signal.

Sounds like it then, or a virus of some kind. Its also likely that you have diseases and insects over there that we don't have here which might have affected the plant. Sorry I can't be of more help.

Thank you anyway.