As others have said, it is extremely unlikely that all these plants would be affected by the same fungal disease. It's also unlikely they would be affected by the same pest. The second picture has some white things on the leaf, any idea what that is?
I would say either there are several different things going on in the way of pests and/or diseases, or the problem is environmental. Is it possible, without compromising your privacy, to show us a picture of the whole garden?
Has the garden had sufficient moisture in the past while, the soil looks a little dry in one of the pictures? Can you also post pictures of the whole plant where there's a problem, in addition to the close-ups above, just so we can get an idea of the extent of the problem. For example I could (when we have leaves here
) go out and find yellow leaves and brown spots on things but that aren't a significant problem. Older leaves will often yellow and fall off.
Is there any pattern to this, for example is it mostly in one area of the yard or are the affected plants scattered about? Are there plants that are not affected? Is there any source of possible pollution (a factory nearby, a gas line, a gas station etc.)
I hope we can help ease your mind but unfortunately sorting out mysterious plant problems requires a lot of questions initially. Another option, as Elaine suggested, is to call the county extension service as they may be aware of local plant problems.
