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Pot's Pesticide Problem

Since pesticides are regulated at the federal level (where pot is still illegal) legalized growers are at a loss for best practices when it comes to protecting their crop.

It goes without saying that growing weed is a little different from growing other kinds of crops. I mean, I don't suspect vegetable farmers lose much sleep worrying about mischievous teens sneaking into their fields at night to grab fistfuls of organic kale (maybe hipster teens). But there's one area where the difference between marijuana and other crops is particularly stark: pesticides, and it has both growers and consumers concerned.

For every other crop grown in the US, the chemicals used on them (like pesticides, herbicides, and fungicides) are carefully monitored and restricted by the Department of Agriculture and the Environmental Protection Agency. There are different limits set for what kind of pesticides can be used and what is an acceptable level of chemicals that can be left behind on a crop (crops we eat, like tomatoes, are treated differently than crops we use for other purposes, like cotton).

But because marijuana is still illegal at the federal level, there are no protocols for pesticides when it comes to growing weed. From the federal government's point of view, you shouldn't be using any pesticides on cannabis because you shouldn't be growing cannabis in the first place.

This has left growers with limited resources for trying to determine the best way to keep their crops healthy and their customers safe.

"Until very recently, it was the wild west: everyone was using whatever they wanted to, whatever they heard about on the internet," said Whitney Cranshaw, a professor of entomology at the University of Colorado who studies pest management for crops. "Some were appropriate, others were inappropriate, but there was no direction from the feds, no direction from the state, no direction from anybody. So they just did what they thought was right."

Recently, states where it's legal to grow and sell medical or recreational marijuana have started rolling out recommendations for growers. In May, Colorado's Department of Agriculture released a list of pesticides and fungicides that cannabis growers can use. Washington state followed suit earlier this month. But the lists are limited—they mostly focus on natural pesticides like cinnamon oil and garlic—and don't provide a lot of info about the potential long-term effects of synthetic pesticides on a crop that isn't just ingested, but inhaled.

"You can consume a large amount of pesticides from the plant by smoking it," said Jeffrey Raber, a chemistry PhD who has studied the effects of pesticides on cannabis with his lab The WercShop. In 2013, The WercShop published a peer-reviewed study on the effects of pesticides on marijuana and found that up to 70 percent of pesticide residues on pot could be ingested through smoking. Aside from the high rate, Raber pointed out that inhaling a chemical very different from eating it.

"Usually the safety limits for a chemical on an inhalable substance are about ten times greater because they feel it's that much more sensitive," Raber said. "You don't have stomach acid and your liver coming at things first. When you inhale things, it goes directly into your bloodstream. That's a very different beast."

The easy solution would seem to be looking to the pesticide restrictions on tobacco. People inhale tobacco the same way they inhale marijuana, so if a pesticide is safe to use on tobacco it must be safe for growing weed, right? Not quite, Raber said. Turns out the EPA has never been all that strict with tobacco regulations: research has shown the tobacco industry lobbies hard to keep its favored pesticides legal, and the list of pesticides commonly used on tobacco is fairly lengthy. Raber said at the end of the day, tobacco is getting mixed up with dozens of other nasty chemicals before it's rolled into a cigarette. If you're getting sick from a cigarette, it's probably not because of a little bit of residual pesticide on the tobacco leaf.

And besides, Raber pointed out that tobacco, though also smoked, is a pretty different product than marijuana. While pot is often prescribed for people going through cancer treatments like chemotherapy to help ease pain and curb nausea, cigarettes are pretty much universally considered a bad idea when you're going through chemo.

So if growers can't look to the government and they can't look to other crops as an example, what's a modern day grow-op to do? For at least one facility, sticking to those natural pesticides is a good solution. Denver Relief, one of the oldest medical cannabis growers in Colorado, uses almost entirely natural pest fighters, according to Nick Hice, the cultivation facility operator and a co-owner.

Along with products like cinnamon oil, lemon juice, and garlic, Denver Relief takes care to keep facilities clean and carefully monitors the environmental controls (like heat and humidity) to prevent the spread of common pot-grower plights like spider mites and mildew. Hice said they do use some synthetic pesticides when needed, too, but once the plants move from their vegetative cycle into their flowering cycle, all spraying stops.

"Even with organics, there's a chance of residual being left on the product," Hice said. "Even if it's not a dangerous residual, it could still affect the product. It might affect the product as far as taste and flavor."

Hice told me better guidelines from state governments (and maybe eventually the federal government) would help eliminate a lot of the guesswork for growers and consumers. He also said easing restrictions to allow growers to move outdoors could have a big impact. Right now, a lot of commercial marijuana growing facilities are forced indoors due to strict regulations, which exacerbates the risk of pests and disease. When plants are outdoors, the natural environment keeps these problems in check, according to Cranshaw: birds eat spider mites before they eat the plants, and mildew has less of an ideal environment in which to grow.

Clearer regulations would also make it easier to distinguish between growers that stick to natural pesticides and those who prefer to use synthetic sprays. Just like pesticide restrictions, the regulations surrounding organic labelling is done at the federal level. Since you can't grow marijuana legally, you can't grow organic marijuana either.

For now, growers and researchers like Raber and Cranshaw were pleased to see some attempts at guidelines from the state level and hope a federal change is on the horizon: either legalizing marijuana, or relaxing the rules so the EPA can at least weigh in on how the crop is grown.

Watch more Motherboard: The future of weed