Branches Question

[dmallia]

I got my first american green tree frog so I built my first vivarium with plantation soil, vine, silk plants, a piece of cork bark and a grapevine branch. After 1 week the grape vine begin to have white mold on it and I thought that the substrate was to watery, so I heated the substrate to dry it a bit. I washed the grapevine branch and left it in front of the fireplace to get warm and remove any water in the branch. I cleaned the vivarium and set it up again but the same thing happens. Do you think that I need to do anything else or change to another type of wood? If so, what would you suggest?

This is a picture of the vivarium right now. I still need to add more plants and hiding places but for now I need to solve this mold problem.