Certain species of wild grass are classified as weeds and can be quite difficult to kill. Perennial species of wild grass may send down extensive and deep networks of rhizomes that keep them coming back year after year even when their blades have been repeatedly cut back. Annual and biennial species put down prolific amounts of seed that may sprout for several seasons after their parent plants have been eradicated. To kill wild grass for good, repeated applications of herbicide may be necessary.
Treat yards or fields with wild grass and no other desirable grasses with a post-emergent broad-spectrum glyphosate herbicide. Spray or scatter the herbicide over the grass according to the manufacturer's instructions, but be careful not to get it on any desirable plants. A broad-spectrum herbicide will kill any plant with which it comes into contact.
Kill wild grass growing among desirable lawn grass or garden plants by treating it with a grass-specific pre- and/or post-emergent herbicide specified for use on the species of grassy weed you are trying to kill. Treat areas affected by annual and biennial grassy weeds with a pre-emergent herbicide two to three weeks before that species' seed is scheduled to germinate (if you want to kill this year's grass as well, use a combination pre- and post-emergent herbicide). Treat perennial grasses that regenerate through underground rhizomes with a post-emergent herbicide when they are actively growing.
Re-treat the wild grass as necessary at the intervals recommended by the herbicide's manufacturer.