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. When most marijuana was grown in basements and backwoods, mold and spider mites could ruin only a few plants at a time. But as legal pot moves to warehouses and commercial fields, pests can quickly create costly problems for growers. Some are turning to chemicals, raising concerns about safety. Pesticides and herbicides are regulated by the federal government, which still regards almost all marijuana as an illicit crop. So there’s no roadmap to help pot farmers. Chemists and horticulturalists can’t offer much assistance either. They sometimes disagree about how to combat the problem.