clematis wilt is a fungal disease caused by the fungus Ascochyta clematidina which is soil borne and affects the plant right at ground level. He says, ‘In 1915 a Bulletin was published which dealt with Ascochyta clematidina, as this fatal disease is named. If those are the symptoms then the plant does indeed have clematis wilt. Healthy Clematis should not suffer from the wilt, however if you have a clematis that is of the large flowered kind ( eg Group 2 varieties ) that has all of a sudden drooped overnight ( or very quickly ) then water in a good quality fungicide Clematis wilt: Plants with dark brown to black Ascochyta leaf spots develop a stem canker that … It’s spread by water splash, and blocks the uptake of water in the stems, causing instant collapse. Control. Ensure good air circulation around clematis stems. Ernest Markham in his book Clematis, published by Country Life Ltd., even has a name for the fungus that is supposed to be the cause of the disease. Remove infected leaves as they are detected. Irrigate plants in a manner that keeps water off the foliage. Many theories have been advanced as to the cause of Clematis Wilt. Clematis wilt is caused by a fungus that enters the plant through a wound made by an insect or an abrasion, such as rubbing from a plant tie. Infected foliage must be disposed of immediately, as the fungus can survive on the plant if left lying on the ground. The best fungicide I have found to treat it is benomyl but i am not sure if that is still available. Clematis Wilt is a systemic condition that only really affects plants that are under sufferance. Affected stems should be cut down to ground level and the remaining stems and the surrounding soil sprayed with a fungicide such as Bio Systhane (active ingredient myclobutanil) or Supercarb Systemic Fungicide (carbendazim). Apply a fungicide to protect plants.