It is likely going dormant and should grow again in about three months. All the major gardens recommend that the tuber not be watered during the dormany period.

Thanks exotic...so should I move it to a dry substrate before everything falls off?

Once the petiole dies you can remove the tuber from the soil and wrap it in damp burlap until it becomes active again. I just leave it in the pot and keep it where it can't get water until it emerges from dormancy.

Most gardens use a lot of sand in their soil mix to make sure the tuber does not rot. Look up the species on the Berlin Botanical Garden site and they offer great information on a good soil mix as well as common problems with the plant.

I tried to find the link on the Bonn Garden site but it appears to have been taken down. The same page can be seen on the International Aroid Society website.

Here is a link that might be useful: Amorphophallus titanum

So do not wait until everything..the petols, the stem fall off. treat it as if it were dormant now?

Once the petiole wilts then it is dormant. If it is already on its way down you will do no harm by taking it out of the soil mix.