Clematis can get a Puccinia rust here in Colorado. This disease is best managed by good sanitation. Remove all evidence of rust in the fall. The rust overwinters on infected parts of the plant that are not removed before growth begins the following spring. You can also prune out affected parts of the plant during the growing season if desired as long as excessive amounts of the aboveground portions of the plant are not removed. Improve air circulation in the area of the clematis by selectively pruning trees or shrubs that may be shading it. Clematis grows best with the aboveground portions warm and the roots cool. Rust on clematis is bright orange in color. If you are not finding pustules of bright-orange material, it may be some other problem, most likely environmental. Clematis generally have few disease problems.

Contact your local Extension office and inquire about their plant diagnostic services.