Unknowns abound in pesticide use for growing pot

Photo: A marijuana plant is in flower at a Denver cultivation facility in 2013. (Joe Amon, Denver Post file)

“There is no federal agency that will recognize this as a legitimate crop. … Pest-management information regarding this crop devolves to Internet chats and hearsay,” says Whitney Cranshaw, a Colorado State University entomologist and pesticide expert

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.

Herbicides and insecticides 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, largely because the plant is used in many different ways — smoked, eaten and sometimes rubbed on the skin.

“We have an industry that’s been illegal for so many years that there’s no research. There’s no guidelines. There’s nothing,” said Frank Conrad, lab director for Colorado Green Lab, a pot-testing lab in Denver.

In states that regulate marijuana, officials are just starting to draft rules governing safe levels of chemicals. So far, there have been no reports of any human illness traced to chemicals used on marijuana, but worries persist.