Clematis wilt is a disease of clematis caused by the fungus Phoma clematidina (formerly Ascochyta clematidina). Many of the large-flowered hybrid cultivars are very susceptible, but the smaller flowered species appear to be much more resistant.
Wilting has long been recognised as a serious problem in clematis. And although it is known that the fungus Phoma clematidina causes clematis wilt, there are cases of wilting when the fungus is not present. Research has clarified two important points:
- Wilting in large-flowered hybrid cultivars may be caused by Phoma clematidina
- Wilting in resistant hybrids and species clematis is very unlikely to be P. clematidina, and is probably caused by environmental problems
So, although all wilting in clematis is often blamed on fungal infection, it is most likely to be caused by environmental problems, (unless it is wilting of the more susceptible large-flowered hybrids).
Clematis is a plant which, in the natural environment, prefers a deep and fertile soil in a moist and shaded habitat. However, in gardens, clematis are often planted in shallow dry soils in exposed sites, often close to buildings. In such circumstances they suffer from root stress which contributes to poor growth and what is loosely described as wilt. Overall, infection by P. clematidina is a problem for the nursery trade and specialist growers, but relatively uncommon in gardens.