Looks like more than one just a light misting should be used, bet if I sprayed it twice those few bits of grass would have died as well.
Caution: This will kill anything, not just weeds, so if you want to keep your roses, don't use this on them.
UPDATE: I left them dead and didn't pluck them, not sure if they came back or more grew but some greenery can be seen in the area a few weeks later, but it did better than last year's attempt with Roundup. After using Roundup, my area looked more beautifully green with weeds several weeks later than before I used the Roundup; it was like I fertilized the area for them. I am assuming I am supposed to pick the weeds, but just haven't the time.