White "stu8ff" on a soils surface usually is a mold of some kind and the presence of that usually indicates atoo wet soil, and that too wet soil not the mold itself is probably what is killing your Tuberose. Of course "white stuff" in a soils surface could also be salts which may then indicate a soil that is too alkaline as well as too wet, but the problem with your plant is soil related so you need to dig into that soil and determine what is the problem.

Or it could be perlite.

What are the size and shape of the white stuff?
And does it move?
How is it killing your plant? Chewing or what?

Can you post an image?

Greetings Kimmsr and Jean001,
It is very small (like pin heads, no it is not moving and it is softening the stem and leaves are just falling apart and the plant is dying..

Although difficult to tell that does kind of look like perlite on the soil. What is the moisture level in that soil. If the soil is too wet, constantly, your Tuberose will rot.