Wondering how often you need to test, each harvest, once a year? 

I'm still thinking that rural "hubs" for testing could be the answer.  Maybe even partially subsidized by the state off the taxes collected. If Thomas can't sell his marijuana, he isn't collecting taxes on it to send to the state either. (or to the City of Nome, assuming they want to tax it too) The "black market" will continue to thrive as well...