Clematis wilt is often the culprit behind a dying clematis plant. According to Gardening Know How, clematis wilt is caused by fungus infestation. Clematis wilt affects the top of the plant and spreads downward until the entire plant dies.
Typically, clematis wilt occurs when the plant has been damaged. For example, insect attacks can cause damaged leaves, which create a vulnerable area on the plant. When clematis wilt occurs, it is best to cut back the plant to remove the affected areas, according to Gardeners' World. Removing the infected areas of the plant generally prevents the disease from spreading to healthy parts of the clematis.