if its straw it will be super for mulch
if its hay less super but i would probly use it anyway but it will have lots of grass seed in it

Agree - if straw it's 100% perfect. If hay, it's only 99% perfect. If you search 'hay straw mulch' you'll find many discussions on using both.

We mow and bale our own hay so we use it annually and apply it thickly (8" minimum) with excellent results. So if it's really hay rather than straw, crack the bales open first and let them dry well before applying and most any remaining seeds will winnow out. What few do survive to sprout can be easily pulled.

Dave

Any green growth you may be seeing in that straw will be from seeds left on the straw after harvest, the same grain the straw grew, Oats, Wheat, Rye, etc. That green growth will not be a problem.