After discovering knotweed in one of my customers garden I did some research on this much maligned plant to discover it is potentially rather good for you due to its high resveratrol content. Infact all the reveratrol suppliments seem to be made from this and not grape vines like the marketing would suggest.
As I had been making other weed sprays and typically they were usually medicinal too. I searched for the potential of this plant too and eventually found the following:
Knotweed extract "induces phytoalexins which infer resistance to powdery mildew and other diseases such as Botrytis". In other words, the extract helps the crop or ornamental plant fight the mold rather than attacking the mold directly. If the extract were made with organic alcohol, the fungicide should be considered organic.
https://www.treehugger.com/lawn-garden/giant-knotweed-extract-an-organic-fungicide.html