Keep removing those webs. I remove yellowing leaves constantly and often will cut off damaged leaves, removing the brown part. It does not harm the plumeria to do so. In fact, when rooting a cutting, you want to cut those larger leaves off, leaving only the tiny, terminal leaves. That directs energy into rooting rather than into those large leaves.
Black Kow is out in the garden centers here, outside with all the other large bags of potting/garden media.
