When I first started planting this spring, I thought the 1-mm-ish black spots appearing on my plants were alive. I.e. fungus or other biological agent of destruction for my young seedlings. However, although they continue to appear on plants young and old, they do not grow. I also notice them now on unliving objects, such as my hose (in photo). Conclusion: atmospheric fallout. Of what? From where?
To be continued…
UPDATE: If you read the comments, I am correctly informed that the insidious ‘black spot’ syndrome is actually biological. Specifically, it is fly poop! And we did have a lot of flies that summer from the chicken poop dotting the yard – a problem we later dealt with by expanding the chicken run.
Sustainable Scientist 
It looks like flecks of… motor oil, maybe? What happens if you lick your finger, then rub the spots?
Just tried this. Not much. The spots are hard and kinda shiny. They flake off if I apply enough pressure at the edge. My current theory is nastiness from the metal smelter located 2 miles from here.
Try calling the Master Gardener or WAZZU extension for ideas on what this could be.I've been dealing with the attacks of the impossibly green (and thus, hard to see) cabbage moth larva. Must be why my cabbage looks like lace. At least the chickens will eat the caterpillers once I find & remove the ravenous green things!
Great idea. I contacted a local NGO (Puget Sound Clean Air Agency) who were remarkably unhelpful – their only comment when I asked for leads on what it might be or who I might talk with was to say the yellow pages have many local private companies who would come and assess it for me. I watch the beautiful cabbage moths dance over (and only over) my cabbage family plot, laying their eggs. Last week I brought in my salad greens and a big fattie was left lying in my basket. Wonder how many I've inadvertently eaten??
Jen,I have these too, I think it might be fly poop. Not sure, but for some reason we are having a bit of a fly problem right now. Every where we have flys we have these spots. Gross, but I guess its better than some sort of pollution.Alison (from the garden tour)
OMG you are so right! Difficult to find online references for images of fly poop, but fecal spots of musca domestica they appear to be! Thank you for solving this problem. Chicken poop all over the yard = robust fly population. Makes sense. Now, how to keep the little beasties down!?