Powdery mildew and/or spider mites are first to come to mind as common on zinnia. But it could be something else - fungal, perhaps.

Al

I agree with Al, with emphasis on the mildew. If it is one of the mildews, you can try drenching the plants with a 'home-brew' of 1 tablespoon milk and 1 teaspoon baking soda mixed into 1 quart of water. Repeat after every rain. Sometimes it helps, sometimes not. Nothing will recover the portions which are dead, but the living plant/s might improve enough to provide you a show of blossoms in a couple weeks.

Another thought is whether or not the saved seed came from hybrid parents -- which do *not* pass the exact hybridized traits into their seeds but instead often revert to one of the grandparents genetics. "Strains", which are not quite hybrids, pass their general characteristics through the seeds - State Fair zinnia is considered to be one such strain. I mention this because I have found saved seed from State Fair does seem to have a great weakness for mildews (shouldn't, but it's happened several times) with the saved-seed-plants often being sickly, small flowered, and mildew-prone. I no longer bother saving that seed.

One of several fungal leaf spot diseases might also be the issue in your part of the country. Bacterial leaf spot could also be a problem. Heat and humidity help create the perfect conditions for the onset of these common zinnia problems. You should see some of mine!

I'm going to cull the offending plants today, and dispose of them. No more zinnias can be planted in those locations (or other disease prone plants). I will never purchase that variety again, either.

I'm going to devote plenty of annual space next year for more of the Profusion zinnias, and of course, Z. angustifolia. Though not the best for cutting, they are tireless bloomers, drought and heat tolerant, and practically disease proof!

If you are interested in a good commercial seed source, let me know.

Sure, rhizo, I'm always interested in obtaining good seeds. As far as the plants that I currently have, I guess I'll pull some of the worst and spray the ret with the recipe Meldy provided. I hate not having my usual zinnias...they normally draw so many wonderful creatures to my yard...and this year it's been lonely out there compared to last :(

Mrs_Emily,

"...They ARE second-generation, grown from seeds I collected last year..."

Do you happen to recall the name of the seed parent?

MM