On CBC radio in Alberta yesterday Catherine was having trouble with her clematis. Parts of the plant were wilting and then browning - or browning and then wilting- I am not too sure. I immediately declared she had trouble with a bacterial wilt. Ooops!
The wilt of clematis is caused by a fungus so I am self-correcting here for all to read. If there is a single stem wilting on a clematis that becomes a few brown wilted leaves or a whole stem of wilted leaves you may in fact have fungal wilt caused by Phoma clematidina. Cutting through a node just below the damage you can see if the stem is blackened and filled with fungus. This is causing the wilting and all damaged material must be cut off (I did tell Catherine to cut off the damage).
If the cut reveals the plant is not black, there is a chance Catherine's clematis was simply wind whipped by all the crazy Alberta weather we've had lately. In that case, the cure is the same: remove the damaged portion anyway.
For further details about this and other organisms causing rot in clematis check out the excellent paper out of England on the same subject: