We have been fighting this menace for over five years but I don't think that works, we had two to three hundred tilapia and maybe twenty catfish, plus palai and turtles also Koi in there before the drought this year, never even touched them.
Glyphosate sounds a good idea, now there is no fish or anything else living at all in the pond as it dried right up and killed everything except these darn lillies, the seeds are like hard small black golf balls but cant see them in the mud.
A few years back we gave some lillies to a friend, two weeks later they had all gone, he said snails ate them, I have no idea what kind of snail or where to find them though.