I used Wipe Out, which isn't sold now, and put the tiniest drop on the centre of the plants. The grass all around the plants turned yellow, but the plants are still green and growing!
I'm leery of using these sprays because the two cats go outside whenever they feel like it. The plants obviously don't spread by seed, because I haven't let them bloom in two years.
On the other hand, the pond is looking good, and the water lily pads just reached the surface. Fish are still alive, even though the little cat drinks from their home. And the hosta's are looking good. So not everything is bad.