I sprayed the Atrazine as directed and it didnt kill the Pennywort. I waited a week and a half and sprayed some areas again and also some new areas.
After another 2 weeks and a couple of rains I noticed some of the Pennywort was dead, but much of the grass around the sprayed areas was dead as well.
In general, it killed more grass than Pennywort.
I have used other brands of Atrazine with mixed results. The good thing about this is that it doesn't hurt my centipede grass, azaleas, day lilies, phlox, etc. However, after three treatments, the weeds are doing great! The only thing that seems to work is Hi-Yield sethoxydim. I am going to treat with the Atrazine once more before I give up on it. My wife is giving me hell...