It is noted that Ernest Markham Clematis won awards in part due to its resilience and resistance to pests and diseases.
Clematis in general have no known serious issues.
Most plants can be prone to common, ornamental (non-lethal) issues caused by various environmental conditions. Clematis may be susceptible to wilt/stem rot (potentially fatal), powdery mildew, leaf spots, rust, and viruses. Potential insect pests include aphids, vine weevils, slugs, snails, scale, and earwigs. Watch for spider mites. Alleviate these common issues with over-the-counter insecticides or pesticides.