Clematis are susceptible to many insect pests and diseases. However, rarely will they kill a well maintained plant. Some common leaf spot diseases include Cercospora spp, Cylindrosporium spp, Phyllosticta clematidina, Ramularia clematidis, and Septoria clematidis. Clematis may also get rust species of Puccinia, blight, and a few root rots like Phytophthora and Rhizoctonia.
One of the greatest attributes of clematis is the mass of blooms on such a delicate looking frame. This can at times also be its downfall. If the plant is not securely attached to its host, the stems can be damaged. The resulting wounds provide a target for a wide range of fungi to attack. The plant then severely wilts or collapses. This malady happens most often when the plant is young. “Clematis wilt” is the catch phrase that has developed to describe this occurrence.
Phoma clematidina (formerly known as Ascochyta clematidina) is the most common fungus to cause clematis wilt, but it is not always the culprit. Other pathogens such as Phytophthora cactorum have been shown to cause wilt. Clematis wilt can occur at any time, however it usually happens just as the flower buds begin to open. The whole plant can be affected or as most often happens, only one or two of the stems collapse. If clematis wilt occurs, it is important to remove and destroy the affected stems. The fungus will remain in the healthy looking part of the stem, so it’s also imperative that about one inch(2.5 cm) of the stem below the infection be removed. New shoots will soon appear at or below the soil line. At worst this therapeutic pruning will delay your flower display. Its very seldom that clematis wilt destroys a whole plant. P. clematidina is capable or growing and reproducing on dead plant material including some common weeds so cleaning up leaf litter can significantly reduce the source of inoculum. If the problem persists the use of the fungicide benomyl will help.
Clematis wilt rarely affects smaller flowered species such as, alpina, cirrosa, macropetela, montana and viticella. Also hybrids that have resulted from viticella crosses such as Madame Julia Correvon and Etoile Violette have proved to be very resistant to the various fungi that cause this problem.
Another fungus that might affect your clematis is mildew. It is seldom a problem until late in the season and not a problem at all if there is good air circulation. If mildew is noticed in its early stages it can be easily controlled by many different fungicides readily available. Your local garden center or nursery will be happy to make an appropriate recommendation here.
Earwigs and slugs are the most common pest problems clematis have. Slugs are the most troublesome. As they will always be with us, it’s a matter of control not elimination. Slugs prefer to attack young shoots, thus slug bait early in the spring gives the best results. Earwigs usually attack in mid summer and can turn the bloom of a late flowering clematis into a lace work over night. There are many good pesticides and traps available to control earwigs.
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