This month you may have noticed shriveling of some stems on your clematis, while others of us have been so unlucky as to experience a dramatic demise of the entire plant shriveling and turning black in a week. These symptoms are typical of a disease called clematis wilt.
These dramatic symptoms most often manifest just as the plant is about to flower, typically striking the flower buds and new growth first. In my research, I have found 2 fungi credited with causing this theatrical demise, Phoma clematidina and Ascochyta clematidina. These pathogens enter the vine’s vascular system and clog the fluid-carrying tubes causing all parts of the plant above the clog to wilt as if it needs water.
Luckily, this disease does not attack the roots. Simply prune out the affected stems or trim the plant to the ground. New shoots will emerge and some cultivars will bloom again in the same season. Be sure to disinfect your tools after pruning the infected plants to avoid transmitting the disease to other plants.
Once the plant has established heavy, tough stems the problem appears to lessen. In other words, the plant can outgrow the disease. These symptoms have lead some gardeners to call the disease “juvenile wilt disease”.
These fungi appear to primarily attack early-season, large-flowering hybrids. If you would like to avoid the trauma of seeing your entire clematis shrivel up and die, plant small-flowered species like Clematis montana, C. macropetala, C. alpine, and C. viticella.