African Daisy

I came home from work and went straight to planting the flowers I bought on Friday. 2 Icelandic poppies, 2 cosmos, and two African daisies. After they were planted, I started weeding the flower bed in the back yard. In this bed I get a weed that is very difficult to get rid of, it looks like a this blade of grass and the roots are long. I think the mulch that was put in this bed had seeds of this weed in there because I don’t get this anywhere else and it takes over the whole bed. Does anyone know how to get rid of it? I don’t mind the occasional dandelion, but this is relentless.