One day your clematis vine is thriving and ready to flower; the next day it’s withering before your eyes. What happened? Chances are, it’s been hit by a fairly common fungus that affects clematis plants, called clematis wilt. Clematis wilt can kill the entire top of your clematis vine, but the roots should still survive. If you identify the problem and act quickly you'll increase the chances of your plant recovering.
Identifying Clematis Wilt
Clematis wilt is a fungus disease (Ascochyta clematidina) that is also sometimes referred to as clematis leaf and stem spot. Clematis wilt causes the foliage and stems of your clematis vine to dry and whither, possibly even turning black. Initially, you may start to see reddish lesions along the stems, but the onset and spread of clematis wilt can be quick. That means you may not have any warning before an entire clematis vine turns brown. However, it’s not unheard of for only a few stems to be affected, so if you see sudden discoloring, take heed.
What Causes Clematis Wilt
Clematis wilt is spread by spores that likely remained in the area on the debris of last year's vines or possibly were carried by the wind from another nearby clematis plant. Like most fungal diseases, it is more prevalent during damp or humid weather. When clematis vines are thick and tangled and remain wet well into the day they are at increased risk for the disease.
On older clematis plants, the woody portion near the ground is often the first area affected. This may also be the area where the spores over-wintered.
Once affected, the plant begins to die back because the fungus cuts off its vascular, or circulatory, system and no water can be carried through the plant. Left untreated, clematis wilt will spread throughout the plant and can kill a heavily infested plant.
Treating Affected Plants
The good news is that clematis plants can recover from wilt because it does not attack their root system. The bad news is that you can lose the entire top growth of your vine, often during flowering time.
To give your clematis the best chance of surviving clematis wilt, at the first sign of withering or drying, cut the affected stems back to ground level. It sounds severe, but it can save your plant. Dispose of the cuttings rather than composting them.
Since the roots are not affected, new shoots should emerge from the base shortly after cutting. If your plant does not re-sprout within a few weeks, don't give up. Extension sources have reported plants growing new shoots up to three years after being cut back. Keep the clematis roots watered even if there is no top growth.
Preventing Clematis Wilt from Coming Back
To reduce the chance of clematis wilt re-infesting next year, remove all remaining vine and leaf growth in the fall and dispose of it outside of the garden—somewhere other than your compost bin. The fungus can easily overwinter in the dead foliage.
If you wish to use a preventative fungicide, sulfur is recommended. Treat the plants in the spring, when new growth first appears.
Which Plants Are Susceptible?
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. There is also some evidence that the older and more established a plant is the less likely it is to become infected, but there is no guarantee. The best you can do is keep your plant in good health, prune appropriately for your type of clematis, and be on the alert for any signs of the disease.