These are leaf spot diseases caused by different fungi. Leaf spots are very common on these and many other perennials, shrubs, and trees this time of year. Despite the eyesore they can create when the symptoms are extensive, such infections do not generally threaten the long-term health of the plant, and they should regrow normally next year.

Fungicide is not able to cure existing disease, and while it may help as a preventative measure in a future year, applications would need to be made several times a year, every year, to maintain protection. Aside from the hassle and cost of that process, fungicide residues might harm pollinators or other organisms, so we rarely recommend their use when the life of the plant is not at stake.

Instead, you can rake up and remove the shed leaves from these plants later this fall, after they've withered from frost. You can put them in a compost pile if you maintain a "hot" active pile (that is, not a passive cold pile), otherwise the debris can be thrown out or sent away with yard waste pickup (as municipal landfills would hot-compost the material). That won't guarantee that infections won't recur the next year, but it can reduce the abundance of spores overwintering around the base of the plant.

Plant disease spread and severity can be greatly influenced by weather, so years with drier spring or early summer conditions may have less incidence of diseases like leaf spots. If you irrigate the plants during drought, try to either avoid getting the leaves wet, or water early enough in the day so that they can dry off by nightfall. Some cultivars of Black-eyed Susan are more resistant to leaf spot diseases than others, and the same may be true for hydrangeas.

For now, just monitor the plants for watering needs, since many areas are still in drought or near-drought conditions that can stress roots.

Miri

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