Sorry...nothing to be done. It may continue to grow or it may not. Shoots abort all the time, even on mature plants.

Here are some photos if it helps any.

This is the either dead, or just not growing shoot
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This is the new culm that was a shoot about a week ago and came up after the "dead" shoot.

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Both

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Although it is probably not possible, if you have a way to help me save this shoot, please let me know. This is the only Ph. Nigra I have left.

It looks alright to me. Just keep it watered, and it'll probably be fine.
I've been really impressed by my Nigra, which was planted at the end of February.
Many, many shoots are sprouting...even from the culm-less rhizome cuttings. So,
I'd say have faith. Two of my shooting culms seemed to have died earlier in the
season, but now they've simply "bushed" out around the stunted central culm.
A few culms shot up in the last three days even.

Josh

looks fine to me, just leave it alone , ive noticed on my nigra, that sometimes it stops growing for a few days or so, or even a week, using its enengry for an other culms . my vivax grew a shoot 2ft tall, then stoped, after a week, it sprang another foot..... be calm..

Death has occured... It died. It is outting up a few more, hopefully they wont do the same thing. :/

Leave it there, you might get a bush out of it.