I would turn it into
biochar.
If you use anything that has had fungicide used on it you run the risk of killing off the very organisms you are wanting to promote to grow.
While many herbicides advertise their half life, the studies usually figure this only for usefulness at surface level, not for when the sprayed items are dug into the ground or even were they to be used as mulch.
Roundup is such a herbicide, the half life is reported as short and yet we can find it for months after the plant material has been dug into a field as a "manure". This means the half life is only relevant for it doing the job it was developed to do, not persistence of the compound.
In the end it is all up to the individual. I personally, will not use anything that I find (through testing in my lab) that has even the slightest amount of any "cide" being used on it.
My straw and hay comes from a farm where they practice no spray organic horticulture. It is free of any pesticides, herbicides and fungi/ bacteriacides. It is the only place I will by straw and hay from.
For me this makes the best sense for my hogs and my gardens / orchards.