I actually had a very similar situation happen with a clematis vine. And it smelled horrible!!! I literally poured H2O2 (3%) all over the top of the soil after draining the putrid standing water out of the container it was in. I had no hope, but do you know the hydrogen peroxide worked. I have that vine still to this day. I also had a disease attack the trunk of a Brugmansias too. I squirted H2O2 directly on the diseased part of the trunk. Another plant that I thought was a goner. I did that treatment twice. I even treated the soil above the roots in a desperate attempt to save this favorite plant. It took a few weeks after that, but eventually the trunk healed. I also still have that plant as well. They now are very healthy and continue to grow and bloom for me over the past several years since treating them. To me, H2O2 is a miracle product.
