I understand any of the Roundup chemicals mentioned here work best just as the plants die off in the fall (or whenever they die off in Texas). When they are dying back in the fall the nutrients return to the roots for next year's growth, just like most perennials do. Spraying as this happens causes the plant to pull the toxin into the roots, killing the plant. I only had cattais one time, and by chance sprayed they in the fall. That was 10 years ago and they never came back. I certainly wouldn't let them grow all year and just wait until fall, but treating them at that time probably gets the best results.
Bing
