Depends on the exact kind you have it seems, poison.works according to tx a n m but there is a big potential for fish loss due to oxygen depletion from all the dying spike rush.

Hydroraking is more time consuming and laborious, but seems the safer bet

Here’s the article from Tamu , you might have the kind one species of carp will eat

There’s not just one spike rush

https://aquaplant.tamu.edu/management-options/spike-rush/

CD