"We have an industry that's been illegal for so many years that there's no research. There's no guidelines. There's nothing," Frank Conrad, lab director for Colorado Green Lab, a pot-testing lab in Denver, told the Associated Press.
And while there have been no reports of human illnesses caused by chemicals used on marijuana, people remain concerned.
This spring, Denver quarantined tens of thousands of marijuana plants at multiple growing facilities over concerns about use of unauthorized pesticides. Tests revealed the pot was safe, but two producers voluntarily destroyed their plants and eight others still have some plants in quarantine, the AP reported.
In Oregon, a June investigation by the Oregonian newspaper found illegal amounts of pesticides on products ranging from marijuana buds to concentrated marijuana oils. Other pesticides detected on the marijuana are not regulated by Oregon's newly formed marijuana laws.
Pesticides and herbicides are regulated by the US Environmental Protection Agency, which still considers almost all marijuana as an illegal crop.
"There is no federal agency that will recognize this as a legitimate crop," said Whitney Cranshaw, a Colorado State University entomologist and pesticide expert. "Regulators just bury their heads, and as a result, pest-management information regarding this crop devolves to Internet chats and hearsay."
There is not much more help from chemists and horticulturalists either, who sometimes disagree on possible solutions, because the plant is used in different ways: smoked, eaten and even rubbed on the skin.
States that have legalized marijuana are just starting to draft legislation outlining safe levels of chemicals. However, California, which is the country’s largest marijuana producer, has zero regulations for growing legal pot.
That means some marijuana growers are simply guessing when it comes to pesticides.