Hay germination

[Grizbi]

@Carl, I have exactly the same shoots, however, not in the hay but in the straw that I spread in the fall (not in the vegetable patch). Same seed, same germination in the straw too. I have not yet allowed to set up because having a small area I systematically weed.
For once I confirm that my mulching (straw) was not done in sufficient thickness. I just mulched the same straw with the same straw at the front of the house because I was no longer doing well with weeding. To see if this stroke here the thickness will be sufficient to prevent this germination.
Same case as you, I have an intermediary so it is not possible to identify the source / origin of the straw.
So I will follow this post carefully.