New growths are black on my Den. Bracteosum

[solstice]

Hi everyone,

I have a Den. Bracteosum that's pushing out new growths with leaves that emerge black from the top of the growing stem/cane (I hope the attached pictures illustrate). This means that all new growths stop growing after their first two or three weeks because the bit from which new leaves emerge is essentially dead even if the rest of the cane is alive.

Some of the more mature leaves also have black tips and I also have some leaves turn yellow and fall off. I know that this is not in itself anything out of the ordinary but they yellow out from a black spot (again, I hope the attached picture illustrates what I mean) and I suspect this is related to the new growth emerging black.

I have already started treating with Physan 20 about once every two to three weeks and the situation seems to have improved in that the blackening is not as severe and confined mainly to leaf tips, giving new growths a better chance to mature.

Any tips/suggestions/ideas would be most appreciated as I am so looking forward to this flowering and I hope the plant can make it to that stage in one piece.