(Phoma clematidina – or physical damage)
Clematis wilt disease causes clematis plants to wilt rapidly. However, most suspected cases of wilt are actually caused by physical damage to the stems.
- Leaves and leaf stalks turn black – not brown
- Leaf veins take on characteristic purple colour
- Affected stems wilt rapidly – literally overnight
- Infection can also start through the stems, which have a black internal discolouration
What is clematis wilt?
Clematis wilt disease causes clematis plants to wilt rapidly – in a matter of hours. The leaves and leaf stalks turning black (not brown) is the main symptom. When the leaves turn brown, this is more characteristic of clematis powdery mildew disease or physical damage to the stems.
Clematis wilt disease mainly attacks large-flowered, summer-flowering varieties. Early- and late-flowering species and their varieties are rarely affected.
Most suspected cases of wilt disease are actually caused by physical damage to the stems. Clematis stems are very brittle and easily damaged. Once this damage occurs, water can’t be carried from the roots to the top of the plant, which then wilts.
Another cause of wilting is infection from the bacterial disease clematis slime flux.
Whether wilting is caused by the disease or by stem damage, providing the plant is otherwise strong, new shoots should be produced from the base of the plant or from below ground level. Repeated attacks from the disease will weaken the plant and may eventually kill it.
What does it affect?
- Clematis – mainly large-flowered, summer-flowering varieties
What is clematis wilt caused by?
The causal fungus of clematis wilt disease, Phoma clematidina, survives in the soil on dead clematis leaves and stems. In spring and summer, infection occurs when its spores are carried to the leaves and young stems, including when splashed upwards by rain or water droplets. The infection spreads rapidly to the stems and leaves.
The roots are usually unaffected, and otherwise strong, healthy plants usually produce new growth from below ground level.
How to control clematis wilt
Control depends on whether it is the disease that has caused the wilting or physical damage to the stems.
If physical damage to the stems is the cause of wilting, then try to reduce or remove the causes. This wilting can be caused by:
- The stems of clematis are brittle and easily damaged. They can twist and shatter in windy conditions. So ensure they are strongly secured to their support. Plastic mesh (sometimes sold as clematis netting) is the best, as there are lots of places for the clematis tendrils to grab on to, resulting in a strong hold and no movement or twisting in the wind.
- Slugs and snails and even earwigs or caterpillars will often chew through stems, or even just remove the outer layer of the stem, again resulting in damage that leads to wilting.
- Careless hoeing or weeding around the base of the plants can make wounds that will lead to wilting. Place stem protectors, or even sections of plastic pipe or a cut-up lemonade bottle at the base of the plant (sliding it over the stems to make a collar) to protect the stems from a careless hoe or weeding fork.
Providing the clematis was planted deep enough (always plant large-flowered varieties around 15cm/6in deeper than they were growing in the pot), there should be plenty of underground buds to produce new stems.
Clematis wilt disease is always worse on plants under stress, so always plant them in good soil (slightly alkaline, well-drained with lots of added bulky organic matter) and keep the soil moist during periods of dry weather; when in growth, clematis need a minimum of 9-litres (2 gallons) of water per week. Heavy clay soils are the worst for clematis, so thoroughly dig over an area of at least 1sq m (1sq yd) and thoroughly improve it with organic matter before planting.
Adding a 5-7.5cm (2-3in) deep mulch on the soil around the stems will help conserve soil moisture. Placing large stones will have a similar effect and help shade the base of the plant, which is beneficial for clematis.
Prune out affected stems, cutting them down to ground level or down to below where wilting has occurred. Dispose of all diseased growth by either burning it or putting it in the council’s green waste bin. Don’t compost it.
Carefully pick up or rake up affected fallen leaves – especially in autumn – to try and reduce carry-over through the winter.
It may be possible to protect plants from attack by spraying in spring and early summer with a fungicide, such as Bayer Garden Fungus Fighter or Scotts FungusClear Ultra.
Use plant protection products safely. Always read the label and product information before use. Plants in flower should not be sprayed due to possible danger to pollinating insects. Either spray early in the morning or late in the evening when pollinating insects are less likely to be active.
It is difficult to protect plants from clematis wilt disease – but a lot easier from physical damage. To prevent the disease occurring in the first place, grow the small-flowered species and their varieties, such as Clematis alpina, C. armandii, C. cirrhosa, C. macropetala, C. montana, C. orientalis and C. tangutica.
- Stem protectors
- Mesh supports and clematis netting
- Slug controls