Well,you won't like what I have to say. That looks like one of the forms of fusarium.If it is, the entire plant carries the infection. It is incurable and the entire plant,along with the bin and potting soil should be destroyed. It is also contagious so keep it well away from your other brugs until you can dispose of it. Google brugs + fusarium and read it and weep. Those of us who have grown brugs for a long time have all been there.
