I have a 'rusty leafed' running bamboo in a container and separated from my in ground clumping bamboos to prevent contagion. However, taking a leaf to the nurseries has stumped them and no one knows what it is. They suggested I chop it back and the new growth would be free, but the new tender shoots already have it. I suspect it is some sort of fungi but don't know how to deal with it. Thank you for any help.