Growing marijuana takes vigilance, even when it’s legal. Like any crop, cannabis plants are prone to pests and disease—from tiny leaf-sucking spider mites, which can spawn a new generation in less than a week, to powdery mildew, a fungus that forms a talcum-like coating on leaves and spreads rapidly through greenhouses. For every other agricultural product, there is a relatively clear solution: Find a pesticide labeled for the specific plant or setting, and apply it according to the instructions.
Not so with pot. Discrepancies between state and federal laws have left cannabis farmers without any pesticides approved for use on their crops—and as a result, some growers have taken the matter into their own hands, treating their plants with alarmingly high levels of pesticides intended for other uses.
Although recreational marijuana is now legal in four states and the District of Columbia, and medical use is allowed in 19 more, the drug is still illegal at the federal level: The Drug Enforcement Agency classifies it as a Schedule I substance, considered the most dangerous, along with ecstasy, heroin, LSD, methaqualone (Quaaludes), and peyote. As for pesticides, the Environmental Protection Agency is responsible for registering the labels that guide use across the country. These labels, which explicitly state how and where to use the products to minimize health risks, are legal contracts—states can’t allow the use of pesticides that aren’t approved at the federal level. Because of its Schedule I status, though, no label for marijuana exists, meaning cannabis farmers are left in agricultural limbo.
“The issue with marijuana is there is no federal oversight provided. EPA is not saying which products should be used and shouldn’t be used, which you get with every other agricultural crop that’s out there,” says Randy Simmons, the deputy director of the Washington State Liquor and Cannabis Board. “So a lot of it right now is just trying to go down this dark alley to figure what works, what doesn’t work, what’s best for the consumer.”
Without that oversight, some states are creating their own lists of approved marijuana pesticides. For example, the departments of agriculture in Colorado and Washington, both of which have legalized recreational and medical marijuana, offer information on pesticides that may skirt the legal issues. Most of the products they name contain active ingredients that have low toxicity and are considered minimal risk, like petroleum oil, soap, and sulfur, making them exempt from EPA rules on pesticide residues.
The trouble is, the low toxicity of these products means most of them aren’t powerful enough to protect plants from spider mites, powdery mildew, or other problems marijuana growers commonly face. “Some of the tolerance-exempt pesticides have some efficacy, but if you have a severe infestation or outbreak these aren’t necessarily the products you would use,” says Erik Johansen, a policy assistant for registration services at the Washington State Department of Agriculture.
Since more effective pesticides aren’t legally available, some growers have been sneaking in the use of stronger—and potentially harmful—chemicals. An investigation by The Oregonian in June found medical-marijuana products on dispensary shelves that had allegedly tested clean for pesticides actually contained residues from household roach killer and other materials that shouldn’t be used on consumable crops.
Also in June, a white paper published by the Cannabis Safety Institute (an advisory group that provides research to the legal marijuana industry) revealed that many cannabis products contained pesticides at levels higher than what’s typically allowed for edible or smokable products. Of particular concern were the concentrates used to make candies, baked goods, and other edibles. Examples include concentrate samples with levels of carbaryl—a chemical typically used on fruits, vegetables, and ornamental plants—as high as 415 parts per million (by comparison, the tolerance for carbaryl on blueberries is three parts per million). Myclobutanil, a fungicide used to fight powdery mildew on vegetables, fruits, and leafy greens, was found at eight parts per million in pot flowers, and between 44 and 392 parts per million in concentrates (levels allowed on food items usually range from 0.1 to 10 parts per million). The paper also found residues for pesticides that aren’t allowed on any food crops.
“When I saw a hundred-plus parts per million, I definitely thought it was problematic,” says Rodger Voelker, an analytical chemist, the lab director at OG Analytical (a private company that does cannabis-pesticide testing), and a co-author of the white paper. “Even if there are no direct obvious health consequences, which we don’t know, the bottom line is that levels like that are considered unacceptable for normal agriculture simply because when you see levels like that, that’s an indication of misuse.”
Whether there are direct health consequences to growers and consumers is unknown because there is virtually no research on how pesticides may affect people working with or consuming marijuana. Usually, companies that make pesticides will contract with third-party labs to test their pesticides’ toxicity, and then hand the labs’ data to the EPA to get their labels approved. Because of cannabis’ federal drug scheduling, going through that process with marijuana-specific pesticides would be a non-starter.
But so far, many universities have been hesitant to get involved in research surrounding marijuana cultivation, including pesticide research. For example, Washington State University’s extension program, which provides scientific education in farming communities throughout the state, has forbidden its employees to work with cannabis growers “until there is reconciliation of both state and federal law on the legality of this crop.”
“The university has given us instructions that we cannot work with a grower or an association in terms for giving them pest management advice or cultivation advice, or anything to do with crop production,” says Catherine Daniels, the pesticide coordinator and director at of Washington State’s Pest-Management Resource Service. “We can’t help them.”
According to Dave Stone, a pesticide toxicologist at Oregon State University and director of the National Pesticide Information Center, the toxicity of a pesticide depends both on its residue levels and how it is ingested. With pot, the high levels of pesticides in edible products could pose health problems, he says, but at least with ingested materials, the liver provides some protection.
Inhalation is another story, and the scant research on pesticide residues on similar crops, like tobacco, provides few clues as to how inhaled pesticides may affect the body. “Toxicologically, inhalation can pose some risks that are definitely different [than oral consumption] and we frankly have not done our homework to get at what those risks are,” Stone says. “We punted with tobacco as far as I can tell.”
“I’m used to dealing with uncertainty as a toxicologist,” he adds. “But this is a level of uncertainty that is making me quite uncomfortable.”
But forgoing pesticides completely could pose other health problems. While pests like spider mites are mostly a threat for economic reasons, molds and bacteria can contaminate cannabis plants, too, and those microbes can be harmful to consumers. This is especially the case for medical-marijuana patients with compromised immune systems, who could get secondary infections by inhaling pathogens. “If we’re going to have medical-marijuana programs, mold and mildew and microbes need to be part of that discussion,” Stone says.
As more states move towards legalization—Ohio will vote on the issue in November, and 11 more states may have marijuana measures on the ballot on 2016—the lack of oversight on cannabis pesticides will likely affect a growing number of consumers. But so long as federal laws deter industry and academia from working with marijuana, the problem will likely remain one without a solution.
“We need more scientific research,” Simmons says. “And because it is federally illegal, it is hard for the individual states—even though we’re working together and talking—to figure all this out without that research being done.”
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