I have had this question from a number of gardeners lately. It is very discouraging as a healthy plant suddenly begins to die.
The condition is caused by the fungus, Calophoma clematidina, commonly known as ‘Clematis Wilt’. The fungus causes the plant to wilt quickly and can lead to killing the entire plant. The large flowered hybrid cultivars are the most susceptible.
What Does the Effected Plant Look Like?
When the fungal infection occurs, the leaves wilt and the leaf stalks turn black. Leaf infection is followed by rapid wilting of the stems. It looks like the plant is starving for water, but this isn’t the case.
You Can Do a Few Things to Control Clematis Wilt:
1. When y0u plant your clematis, ensure that it has deep and fertile soil in a moist and shaded environment. The planting hole should be 18 inches deep and 12 -15 inches wide. If you are planting two or three clematis together, enlarge the circumference of the hole by 3 inches for each plant . Soak the root ball and tease out the outer roots. The soil will be filled in 2 to 4 inches higher than the clematis was planted in the pot. For a Type 1 clematis, plant at the level of the soil in the pot. Place the clematis at a slight angle in the hole, angling the stem in the direction you want it to grow. Pinch off leaves on the stem that will be covered with soil. Water the plant well and trim off some top growth of the plant. Place mulch over the roots.
2. Keep young plants well watered. Use rose food, tomato fertilizer or 5-10-5 fertilizer to fertilize celmatis regularily.
3. Keep young plants stable. Tie up young shoots or provide a shelter to prevent young shoots from snapping. The opening will create a possible entry point for fungal spores.
4. When you see the wilt occurring, cut out all wilted stems back to healthy tissue and destroy all the affected material. New shoots will be formed at the ground level.
5. Disinfect pruning tools to prevent spreading the spores to a new area.
6. There are no chemicals available to treat clematis wilt.
7. My research suggested that using a solution of 1 tablespoon of cider vinegar mixed with one gallon of water to spray the root area of the effected clematis plant may be successful to control the fungus. I have not tried this method. When I noticed clematis wilt in my clematis, I cut it back to about 6 inches from the ground. It is now coming back with fresh growth.
Plant Resistant Cultivars
Avoid planting susceptible cultivars which include Clematis ‘Henryi’, ‘Vyvyan Pennel’, ‘Mrs. N. Thompson’,’Duchess of Edinburgh’, William Kennett’, ‘Marie Boisselot/Madame e Coultre’, ‘Ernest Markham’, Clematis ‘Comtesse de Bouchard’, C. Jackmanii’, C. ‘Nelly Moser’
Resistant cultivars and species include Clematis ‘Avant garde’, ‘Bonanza’, ‘Confetti’, C. alpina, C. montana, C. orientalis, C. viticella (which is tolerantant rather than resistant), C. integrifolia, C. macropetala, C. tangutica.