We garden as organically as possible and endeavor to avoid persistent herbicides and pesticides in the compost we add to our gardens. I make most of our compost, but we have access to a large amount of spent mushroom substrate. I am concerned, though, that being a straw substrate, and knowing wheat is typically sprayed with glyphosate prior to harvest that there may be large amounts of residual glyphosate in the compost.
Do you know if mushrooms will break down glyphosate? I know they are masters of soil remediation!
If it is likely that the substrate does contain a large amount of glyphosate would it be remediated by processing it through my worm bins? If so, would I then have glyphosate laced worms that would get it back into the compost when they died and broke down? I rarely let my chickens eat my composting worms, but I would also want to know if I would need to avoid that entirely to maintain organic eggs.
I can have the material tested, but that is rather costly, so I would like to know, prior to testing, if it is likely we will have a positive outcome or if we should just decline the free compost.
Glyphosate (Roundup) is not considered a persistent herbicide. Depending on rainfall and temperature, glyphosate is considered to be ineffective after 6 weeks.
Perhaps you are thinking of clopyralid. Washington State University has a comprehensive website about clopyralid. Drs. Cogger and Bary compiled and wrote the content on that website. I have co-authored a number of publications with them, and consider them very trustworthy. Here is a document they prepared about testing compost for clopyralid.
That paper provides an easy and low-cost test you can conduct yourself if you have concerns about the compost to which you have access (lucky you!). I used a similar test as a method for my masters work on municipal-scale compost about 20 years ago. I recommend it.
I, too, have gardened organically for more than 30 years, in Benton County. I appreciate the rigor you apply to your gardening and composting practices. I would not hesitate to use the mushroom substrate. Still, out of respect for your concerns, I recommend the test devised by Drs. Cogger and Bary.