Microscopic bugs and mildew can destroy a marijuana operation faster than any police raid. And because the crop has been illegal for so long, neither growers nor scientists have any reliable research to help fight the infestations.

As legal marijuana moves from basements and backwoods to warehouses and commercial fields, the mold and spider mites that once ruined only a few plants at a time can now quickly create a multimillion-dollar crisis for growers. Some are turning to industrial-strength chemicals, raising concerns about safety. MORE