Black rust / mark on all leaves and stem of musa basjoo
 

What is this caused by?

Re: Black rust / mark on all leaves and stem of musa basjoo
 

Any help please??

Re: Black rust / mark on all leaves and stem of musa basjoo
 

I could be a number of things for you potted basjoo.

The leaves look like a symptoms of fertilizer burn, sunburn or just old age.
Overfertilization is very common for a container plant.
If it is fert burn your plant will sort itself out in a month or two.

Which one? Only you might know from your plants history.

The stems look normal ....under high humidity fungi spores,moss,will grow on the stems and discolor them. Also as the plant ages and old leaves deteriorate the discoloration and fungi growth will speed up until the leaf has reached end of life.

Leaves that loose their water repellency will do this also because more airborne "pathogens" stick to them.
Soon as the days grow shorter the plant will loose the lowest leaves as they turn yellow.
All normal in nature and in my backyard.

.
dead leaf removal by
Hostafarian,
on Flickr

Re: Black rust / mark on all leaves and stem of musa basjoo
 

These black marks are on nearly all the leaves apart from new ones. I have fertilised it and potentially over watered it. As there is a lot of Guttation in the leaves.

Re: Black rust / mark on all leaves and stem of musa basjoo
 

More info:

Soil mix is standard compost non dense mix for potting plants. Free Draining.

Recently upgraded from a 9 Litre to a 29 Litre/7.25 Gallon pot. I want to keep in a pot in case I have to move out.

Growing in a conservatory, with some sunlight and shade. Never been in full sunlight.

I have been occasionally feeding a synthetic fast acting fertilizer for banana plants.

The black marks are on old and newish leaves. Latest leaves do not have these marks but I expect that to change. Currently on 90% of the leaves.

There is a lot of Guttation from the plant which tells me I am overwatering it.

Back in July in 9 Litre pot:

Re: Black rust / mark on all leaves and stem of musa basjoo
 

Everything cincinnana said plus on your latest picture... pot is way to small and I recommend perlite in the soil mix, after moving to a new pot musa do take a while to settle in.

Edit!!! Reread your post, it will take a little time to settle in its new 29 litre pot.

Re: Black rust / mark on all leaves and stem of musa basjoo
 

too much water?