Using hay from an area that was sprayed the previous year

I was offered cut grass/weeds from my neighbor today. He sprays his area every year. He usually lets his grass grow quite big, then cuts it and sprays afterwards. He said that the hay/grass he's giving me isn't treated yet.

Do you think it would be safe to use this kind of hay to mulch around plants? Or is it likely that the plants will "suck up" the chemicals from the previous year? If not around plants, do you think it would be okay to use it for walking paths (but still close to some plants)? If not would it be at least OK to use around trees?

I guess it's not a very strong product though, as his yard is full of weeds each year and there are multiple species (for example dandelions, nettle etc.).

Thanks in advance for any replies!

I think it's important to know exactly what chemicals have been sprayed.

Also, are there any broadleaf plants/trees in the grass/weeds that were cut? If the answer is yes, that's a good sign.

I mostly read about straw being used to mulch around plants because the seeds have been removed.

Have you thought about growing mushrooms to counteract against the spraying?

3year old hay used as mulch screwed me over just the other day. I wouldnt

Here is my experience and you can come to your own conclusion based on my experience.  Years ago one of my neighbors offered all of the horse manure I could take.  I took several trailer loads of it.  I put it in my garden and for years the sectors of my garden that had the horse manure would not grow  broadleaf plants.  I did a bit of research and after doing so I found many people had had the same experience.  It turns out that even after digestion the chemicals can retain their effectiveness.  I was tempted by the free manure.  Can you imagine what it was like to lose a large sector of my garden?  I hope this experience can help guide you in your decision making process.

I have seen several threads here on the forum which talk about hay and chemical burn.

Here is one:

Joe said, "It’s the hay. I was mistaken by something hay guy said to me before and assumed he only used fertilizer based on his response. Neighbors tomatoes are doing it now. So I confirmed with hay guy. He uses the worst of the worst

https://permies.com/t/216367/Potatoe-leaves-curling#1828431

Denis Schwarcz wrote:...  his yard is full of weeds each year and there are multiple species (for example dandelions, nettle etc.).

I think this tells us pretty clearly that it's not a super-persistent chemical that kills everything broadleaf for years and years.

Personally, I would give it a look and maybe compost it in a back corner that I didn't care about. Before I used it on gardens or fruit trees, though, I would make some tea from it and apply to peas and beans in pots. If they grow funny, there is too much chemical residue.