My 1 acre pond filled up in early Winter after being completed in late Summer, so it's not a direct comparison. FWIW I have just pulled the small cattails (as much of them as I could get out) as they have appeared and this approach has been successful at keeping me cattail-free.

There is a smaller (maybe 1/3 acre) pond 1/2 mile away that has a very small watershed (and, I strongly suspect, a seeping dam) which took much longer to fill up. IIRC it was about a year and a half. The owner has never done anything to control the cattails, from what I can see. The cattails that started growing first are still there, now maybe 20 feet away from the shore, looking very healthy. They have been joined by more that cover the area from there to the shore. NOTE: I do not think the original cattails are in anywhere near 12 feet of water.

I would hit the cattails ASAP now that they have appeared. Even if the ones ending up in 12 feet of water end up dying, I think they will "colonize" the edge of the pond as it moves away from them, causing faster cattail growth as the pond fills than if you remove them now.

If you don't have a lot of them and you can check and remove them from the pond regularly, I don't think spraying would be necessary. But if you have a lot or cannot pull them out regularly, spraying would probably be preferrable. Either way, show no mercy.

"Live like you'll die tomorrow, but manage your grass like you'll live forever."
-S. M. Stirling
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