Clematis vines are a popular choice for ornamental home gardens. Large flowered, early blooming varieties are particularly popular. These show stopping, head turning vines both amaze and delight all who cross paths with them. A fairly common disease of clematis to be on the look out for is clematis wilt (Phoma clematidina). You will sometimes hear it referred to as clematis leaf and stem spot. It is a serious fungal disease, formerly called Ascochyta clematidina. This disease is characterized by the rapid wilting and blackening of the clematis vines. Affected vines appear to almost die over night. The good news is the disease is manageable.

What is Clematis Wilt?

Clematis wilt is caused by a fungus known by the name of Phoma clematidina. The fungal spores over winter in the soil and in diseased plant debris. In late spring/early summer, about the time early blooming clematis varieties are in full bud, the fungal spores become active. The fungus typically infects a wound in the plant, near the soil line, causing a lesion that shuts down the flow of nutrients and water in that stem. Infection can however also occur on leaves and on leaf petioles even without a wound, but wounding is usually required. Damp humid weather favours it’s growth. The root system is often not killed and young shoots frequently regenerate from or below ground level. The disease is not immediately fatal, but infected susceptible cultivars typically do die eventually. There is no cure only management.

What Does the Disease Look Like?

Even though the disease appears to happen almost over night, the period from infection to wilting can take from 10 to 40 days (Smith G.R. 1987). The disease first appears as reddish lesions on the stems and dark brown to black Ascochyta leaf spots on the leaves. These spots develop a characteristic ring around the spot. The infection spreads from the leaf to the petiole causing it to turn black. The disease continues to spread to a leaf node on the main stem, this causing girdling (Pavlis R. n.d.). With water and nutrients now unable to reach this area the stems and leaves suddenly wilt and turn brown/black. Freshly affected stems show black discolouration of tissue when split open.

What Plants Are Susceptible To Clematis Wilt?

Clematis wilt can attack any type of clematis. The larger flowered varieties are most susceptible, while some of the smaller flowering varieties, like Clematis alpina and Clematis viticella, show better resistance (Iannotti M. 2020).

Particularly susceptible cultivars include: Clematis ‘Henryi’, ‘Vyvyan Pennell’, ‘Mrs N. Thompson’, ‘Duchess of Edinburgh’, ‘William Kennett’, ‘Marie Boisselot/Madame le Coultre’, ‘Ernest Markham’. Clematis ‘Comtesse de Bouchaud’; C. ‘Jackmanii’ and C. ‘Nelly Moser’ are also susceptible (RHS n.d).

How Do You Treat Clematis Wilt?

Prevention is always the first step. Make sure you are providing the proper growing environment; full sun for some varieties part sun for others, fertile, well-drained, evenly moist soil, and a sheltered site with a neutral pH. Take care when pruning or tying your clematis to supports, as the stems are very brittle. Don’t neglect your pruning duties though as clematis vines that are thick and tangled tend to remain wet well into the day and are at greater risk of being infected. Disinfect any tools that come into contact with clematis. Since plant debris can harbour the fungus cut back group 3 (type C) clematis in the fall and cleanup any fallen debris.

Prune back the affected stems to ground level at the first sign of withering or drying and disinfect your pruning tool after each cut to prevent spreading the disease. Burn or black bag the diseased debris. Clematis roots are not affected by the disease and they will send up new healthy growth.

Look Alike Injury and Diseases

• Wilting of stems is commonly caused by insect pests like slugs and snail who like to feed on clematis. Their feeding can girdle shoots.
• Rodent’s like vole, mice and chipmunks often severe shoots causing wilting and browning, as do rabbits.
• Physical damage (such as twisting of stems in strong winds). This includes accidental damage the gardener may cause when working in and around clematis vines, especially when they are pruning or tying shoots to supports.
• Clematis can also be affected by root diseases such as Phytophthora root rot and honey fungus. These diseases also lead to wilting.

Photo Credits: all photos taken by the author.

References:

Iannotti M. (2020), How to Identify Clematis Wilt, The Spruce. https://www.thespruce.com/how-to-deal-with-clematis-wilt-1402785

I.Cl.S. – Clematis Wilt, (n.d.). http://www.clematisinternational.com/wilt.html

Missouri Botanical Garden, (n.d.). Clematis Wilt. Clematis Wilt (missouribotanicalgarden.org)

Penn State Extension (rev. 2016). Clematis Diseases, https://extension.psu.edu/clematis-diseases

Pavlis R. (n.d). Does Clematis Wilt Really Exist. https://www.gardenmyths.com/clematis-wilt-really-exist/

RHS (n.d). Clematis Wilt. https://www.rhs.org.uk/advice/profile?PID=125

Smith G.R. (1987). University of Canterbury, ‘Leaf spot and wilt of Clematis caused by Phoma clematidina (Thurn.) Boerema’, https://core.ac.uk/download/pdf/35467455.pdf

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