japanese maple

Two of my acers that I have started off growing in pots have hit problems. They are different varieties, not kept together, but both started to grow new leave & before they could fully unfurl, they started to shrivel & one was blackened.The other sign of something ominous is a web like structure covering one of them, although I have not seen what is making the web. I have grown acers successfully for over 20 years but have not encountered this problem before, both were bought at the same outlet.