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 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. Here's how to identify this quick spreading disease and what you can do about it.
What Does Clematis Wilt Look Like?
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. 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 probably remained in the area on the debris of last year's vines, or possibly were blown in on the wind, from another nearby clematis plant. Like most fugal diseases, it is more prevalent in damp or humid weather. If your clematis vine is thick and tangled and remains wet well into the day, it will be even more prone to attack.
On older clematis plants, the woody portion near the ground is often the first area affected.
It 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.
What to Do for Affected Plants
The good news is that clematis plants can recover from wilt, because it does not attack their root system. However, the bad news is that you can lose the entire top growth of your vine, 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 somewhere other than the compost.
Since the roots were 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. Washington State University Extension’s fact sheet said “One resource on this subject states that renewed shoots can appear up to three years after the problem, so do not lose heart if this happens.”
After pruning back the diseased vine, keep the clematis roots watered, even if there is no top growth.
How to Help Prevent Clematis Wilt from Coming Back
To lessen 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 and somewhere other than your compost bin.
The fungus can easily over-winter in the dead foliage.
If you wish to use a preventative fungicide, sulfur is recommended. Spray in the spring, when new growth first appears.
Are All Clematis Susceptible to Clematis Wilt?
To some degree, yes, clematis wilt can attack any type of clematis. The larger flowered varieties are most prone, 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 better established a plant is, the less likely it is to become infected, but it's no guarantee. The best you can do is keep your plant in good health, prune your type of clematis when you should, and be on the alert.
- Clematis Leaf and Stem Spot (or Clematis Wilt), WSU Extension
- Growing Clematis, Ohio State University Fact Sheet HYG-1247-94