http://www.latimes.com/world/mexico-...230-story.html
"The loosening of marijuana laws across much of the United States has increased competition from growers north of the border, apparently enough to drive down prices paid to Mexican farmers. Small-scale growers here in the state of Sinaloa, one of the country's biggest production areas, said that over the last four years the amount they receive per kilogram has fallen from $100 to $30."
Its pretty much following oil and metals, and wheat - pretty much the entire commodity sector.
Deflation is grinding prices down.