Good God, I am literally sick to my stomach. This has been by far the worst thing I've ever experienced as a cannabis grower.
Since my first post in this thread, whatever viral vector infected my plants spread like wildfire, no matter what I tried. Plants that were perfectly healthy one day were clawing and going yellow just a few hours later. I've sought help from everyone available, including the local extension office - who said they would not touch or advise on ​​​​​cannabis.
I still have no discrete answer in terms of what virus (or even if it is a virus) infected this grow, how it started, what the transmission vectors are, or what any possible effective treatment would have been.
I had to make the awful decision today to burn everything and start over. I just filled up an 8 cubic yard dumpster with about 2,500 plants that were almost all perfectly healthy just a week ago.
I first noticed these symptoms in a few plants about 6 weeks ago. At the time I didn't think much of it. Anyone who has grown large quantities of cannabis knows that sometimes you get a few plants that just have weird growth patterns. That's what this seemed like to me at first, and for the first week or two I tried to nurse those effected plants along. So a word to the wise: if you have something you don't know what it is, chuck the plant.
Once I realized that whatever it is was spreading, I spent another week attempting a cure (see elsewhere in this thread for the range of things I tried.)
Perhaps if I had just jumped directly to triage once I identified that it was spreading I could have saved a bunch of them. At this point I'll never know.
Things progressed very slowly up until a week ago, and I had plants that mostly all looked healthy. I had quarantined those affected and started to dispose of them, but about a week ago everything went to hell.
It's kind of surreal having to do what amounts to a mass grave due to viral infection while the entire world is simultaneously dealing with a viral pandemic of its own.