I want to know how to kill them off.
Sedum Rock Plants
Certified GKH Gardening Expert
Remove small infestations manually by digging up the roots.
For larger infestations you will likely need to use a herbicide that contains 2 4-D.
Follow all packaging directions.
If you use a herbicide that contains glyphoste, it will kill everything around it, as it is not a selective herbicide.
You may need to add a surfactant to the soluction. A surfactant is recommended for killing weeds with a shiny or waxy surface.
Repeat the application in a week if the plants still appear green.