Answer: Based on your description I am not certain what happened to your clematis. This is not consistent with the dreaded clematis wilt or with mildew, for instance, which are occasional clematis problems. It sounds a bit like a rust infection but it is difficult to diagnose with any certainty long distance. If you see early signs of it again, I would suggest you immediately consult with your local county extension to try to get a specific diagnosis. Knowing that, together you will be able to determine how to proceed. If it is something that requires a chemical control, they will have the most up to date information on what to use and how/when is best to apply it to maximize results. In the meantime, avoid wetting the foliage if you have to water the plant, and put any fallen foliage or prunings from it in the trash to try to limit sources of reinfection. Also do a thorough clean up around the plant this fall for the same reason. I'm sorry I can't be more specific and I hope it doesn't reappear.
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