The following photo is of a few Provider bush bean leaves I plucked off. To the best of my knowledge, it looks like sunburn, which doesn't really make a whole lot of sense given the situation. I've looked into other problems, but none seem to fit the bill.

http://tinypic.com/r/2w3azw9/7

If anyone has any idea whether this is genuine sunburn, or some sort of bacterial blight I need to dispose of, please let me know.