I agree that vendors selling treated seed usually say so explicitly. It lets them charge more to most commercial growers, though organic growers won't buy it at all. And they will say something like "Do not eat this or feed it to livestock, or at least don't sue us if you do".
I always copy "Treated", and what it was treated with, onto my labels, if the vendor said so or the seed is obviously off-color. The only pelleted seed I've swapped was pelleted with OMRI-approved material, and i think I put that in the comment and pkt label.)
When I buy from a place that mainly sells to market growers, like Tainong Seeds, they treat over half of their seed and always say so.
Also, their treated seed is typically neon-green or other bright color so it is obviously treated . To market growers, the anti-fungal treatment like Thiram is an extra-cost option that they prefer.
If only people read such things, remembered them, and complied with them, I would urge Dave to add something like that to the all-swaps rules: "If you know it is treated with an anti-fungal or other 'cide, you must label each pkt legibly as "Treated" and include that in the Swap List comment." But who reads and remembers all of the rules?
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When someone in the Beta swap said they ONLY wanted organically grown seeds, I went back to check. Some of the packaging said "ORGANIC" in large print on the pre-printed generic envelopes, though they typically did not mention that in the fine print printed for each separate variety packed in that generic kind of envelope.
Since it only said "organic" and not "certified organic by XYZ agency", I wonder how much that means. If it were Burpee or Parks, I might guess cynically that they "accidentally"-deliberately use generic packaging so they can make everything look organic, but I trust Johnnies and Territorial to not deliberately mislead.
Edited to change "anti-fun gal" to anti-fungal. If we have any gal's here who are anti-fun, I don't wanna know about it!