Farmers who grow marijuana for Colorado's legal market are running into problems as they try to control mildew and pests. Because of the plant's illegal status at the federal level, a main source of agricultural guidance isn't available to pot farmers.

Attempts to regulate marijuana production often hit another problem, as the plant's wide range of uses sets it apart from many traditional food crops.

"You don't smoke tomatoes, you don't smoke grapes," John Scott of Colorado's Department of Agriculture tells the AP. "You don't extract those into oil products that'll be either used through dermal products, through lotions, or infused into other foods."

Last month, The Oregonian reported that "a combination of lax state rules, inconsistent lab practices and inaccurate test results has allowed pesticide-laced products to enter the medical marijuana market."

After commissioning independent testing of 10 marijuana concentrates bought at dispensaries, the newspaper reported that nearly all of them contained pesticides. The Oregonian said 14 chemicals were found, including a half-dozen the federal government has classified as having possible or probable links to cancer."

This spring, Colorado farmers who were suspected of using toxic pesticides had thousands of plants placed in quarantine; some plants were later destroyed. And the uncertainties also extend to some regional extension agents, who routinely provide ground-level advice and guidance to farmers around America.

"In the absence of any direction, the subject of pesticide use on the crop has just devolved to just whatever people think is working or whatever they think is appropriate," one extension agent, Colorado State University entomologist Whitney Cranshaw, told member station KUNC in May.

To try to fill that void, Colorado has published a guide to using pesticides in marijuana production, along with a chart that lists commercial products, their active ingredients, and any safety concerns. Reflecting the change that's inherent in the marijuana industry, the guide includes a chart that the state updates with new information.

Guidance can vary depending on whether the growers are commercial or private — and whether the finished product will be eaten or smoked.

As The Week reports:

"Recent investigations in Oregon and Colorado found unapproved pesticides on commercial marijuana buds and in other byproducts, or pesticide residue above legal limits. One fungicide commonly used on cannabis plants, Eagle 20 EW, is regularly used on crops like grapes and hops, but it is considered toxic when burned and is banned in tobacco, for example."

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