Hi folks.

I scattered some runner beans along a fence and they started out well, but now they've developed something which looks like a disease to me, but could be anything as far as I know. At first it looks like discolored spots on the top which then turn more towards white and spread until the leaf is pretty much destroyed. I'm including one picture here of what it looks like when it gets really bad, in the hope that someone could help me identify it. I can post more pictures if it'd be helpful. I thought maybe it's halo blight, but it didn't look quite like pictures I'd seen online.

Thanks!

Image link: