That’s the diatomaceous earth. I kind of spread it everywhere as I wanted the gnats gone and anything else that might of been lingering. So I covered leaves top to bottom and soil. I have been using sprays which has washed most of it off but there is still residue from it. It’s a white powder formI am unsure to what caused the white mildew though, and it worries me, and I would suggest dealing with it before anything. I’m so sorry your dealing with all of these problems. I wish your experience was going smoother for you.