What is clematis wilt?
Clematis wilt is a disease of clematis caused by the fungus Calophoma clematidina (syn Phoma clematidina, Ascochyta clematidina). Several 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. Although it is known that Calophoma clematidina causes clematis wilt, there are many cases of wilting symptoms in clematis recorded where the fungus is not present. Research has clarified two important points:
- Wilting in large-flowered hybrid cultivars may be caused by Calophoma clematidina, in which case it should be possible to find some of the symptoms described below
- Wilting in resistant hybrids and species clematis is very unlikely to be C. clematidina, and is probably caused by cultural problems, other diseases, or pests. These other problems are equally common on the large-flowered hybrids
So, although wilting in clematis plants is often blamed on C. clematidina, unless it affects one of the more susceptible large-flowered hybrids it is most likely to be caused by something else. On any clematis, wilting of shoots is often the result of problems such as grazing of the stems by pests (e.g. slugs and snails) or simply physical damage (such as twisting of stems in strong winds). Both hybrid and species clematis can also be affected by root diseases such as Phytophthora root rot and honey fungus, and because the root system is unable to function properly wilting will result.
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 severe stress which contributes to poor growth and what is loosely described as wilt. Overall, infection by C. clematidina is an occasional problem for the nursery trade and specialist growers, but relatively uncommon in gardens.