The damaging fungi are frequently found on the leaves of clematis and may even make lesions on the leaves. However, lethal damage is only done when the fungi penetrate the stem through the nodes; this is especially prone to happen if the stem has been damaged. Young green clematis stems in conditions of humidity and at a temperature between 20-25ºC are unable to summon defence mechanisms to counter the invasion by the fungi. A characteristic lesion is then formed at the node (See plate - later). For a distance of about 1.5-2ins (4-6cms) near the node the tissue is destroyed. The damaged area at the node becomes a characteristic black colour. As the area around the node dries the tissue falls out as a dry black powder. The area above the node turns greeny-brown, then brown and brittle and dies. The stem below the affected node remains green. The lesion extends right across the stem; this is why the action is so damaging as no sap can pass the node. Thus the stem above the node wilts as if the stem had been physically severed.

The selected node in my experience is invariably close to the ground in the bottom four nodes. It can however start at an upper node or even a node on a branch stem. In the past there were many speculations on the nature of clematis 'wilt'; had the stems been cut open the obvious and incontrovertible cause of the stem death would have been seen. See: Howells, J. 1996. The Lesion of Stem Rot. The Clematis. P.54.

This photograph illuminates the fungal 'stem rot' (wilt) in clematis. Two clematis nodes (marked with an arrow) are seen here. The right node has healthy green tissue above and below it (the flow from the roots upwards is indicated by red arrows). The left node has healthy green tissue below it but at the node itself this tissue has been destroyed by fungus leaving a black mass for about 2in. (5cm). Above the left node the tissue is cut off from nourishment by the fungal infection and the tissue turns brown as it dies. See: Howells, J. 1996. The Rose and the Clematis as Good Companions. U.K. Antique Collector's Club. P.170

When a stem 'wilts' it should be severed across the green part of the stem below the dead area of the stem. This is invariably low down on the stem. Thus cut the stem just above soil level if the whole stem is involved. The end of the stem left in the ground will show its green face to you and you will know that the lesion is above this level. The lesion can be identified using one of two ways after placing the stem lengthways on a table:

1. Chip away with a sharp knife at each node starting at the bottom node of the stem. If wilt is present you will quickly see the black area in one node. Below that node the stem is green, at the affected node it is black and the stem is brown above.

2. With care and using a sharp knife or razor blade knife it is possible to start at the bottom of the stem and slice up the middle of the stem dividing it into two parts. Sharp scissors will also do this work. As you start up the stem you will be in green tissue, at the affected area this gives way to the characteristic black lesion and above is the brown dying stem.

If you do not find the black area then your clematis has not died from `stem rot' but from one of the other causes of wilting.

Your next action is crucial. Stem rot rarely kills clematis. The gardener is the killer. The inexperienced assume the clematis is dead and give it no further care. Thus it dies. The correct action is to gently explore the top half inch of soil around the stem. Frequently you will find that the roots are already sending up shoots. So often does this happen that it is tempting to speculate that the roots have already re-acted to the fungal pruning of the stem by throwing up shoots. To find the shoots will confirm your belief that the plant is alive and needs your care. If no shoots are apparent then keep up your usual care, especially watering, of the plant and shoots will soon appear.

Additionally, of course, fungicides should be employed for preventive puposes but the long term solution to stem rot is to remove C. lanuginosa and its progeny from the hybridising programme. See: Howells, J. 1996. The Lesion of Stem Rot. The Clematis. P.55.