Straw as mulch turning black?

[Grandma99]

I had a bale of straw seeding mulch with tack https://www.amazon.com/gp/product/B00GR ... UTF8&psc=1

It had been sitting outside in its original bag through the winter. I notice the bottom of it is turning black and, in fact, the 'black' is spreading a bit up the sides of it. Is that harmful to my plants if I use it as a mulch (top dressing)? Or is that 'black' just it decomposing because it got wet and it's not a problem? Is it a fungus or ?

[ACW]

I would say no problem,it will rot down nicely into a soil improver!

[rainbowgardener]

Probably mold or mildew from having the water held in. Once you spread it out in the sun, it will dry out and be fine. If you take it out of the bag before you let it sit, it is less likely to get mildewed. On the other hand, mice decided my straw bale made a nice winter home.....

[Grandma99]

Thank you very much! I set the straw in the sun and the black is disappearing; it must have been a mold.