David Martinez, manager at 3D Cannabis Center in Denver, makes labels in the grow room in December 2013. (RJ Sangosti, Denver Post file)

Pot pesticides: What exactly are these chemicals, and why are they banned?

The five most common banned pesticides seen in pot recalls issued by Denver's Department of Environmental Health

The marijuana industry has a pesticide problem.

In the absence of federal guidance on pesticide application — the U.S. Environmental Protection Agency regulates the use of pesticides throughout the country, marijuana is still federally illegal, the EPA won’t allow cannabis on any pesticide’s label, yada yada — pot growers have long been using pesticides they shouldn’t have been.

As pesticide regulations are under scrutiny in Colorado, Oregon and elsewhere, some Cannabist readers have asked the question: “What are these pesticide chemicals, anyway, and what makes them so bad?”

So we wanted to list the five most common banned pesticides found in recalled marijuana products in Denver — and what the experts know about them. Mind you, research on pesticides and cannabis is lacking, given that whole federally illegal component of this situation. These pesticide chemicals are allowed on some food items, but given marijuana’s unique pattern of use — where the cured plant materials are exposed to high levels of heat and then inhaled or eaten — there’s nothing in traditional agriculture to compare it to.

You’ll notice that some of these pesticide chemicals are more toxic than others, yet they’re all banned by the Colorado Department of Agriculture for use on cannabis plants. The pesticides local growers can currently use have labels so broadly written that the state determined their use on marijuana is permissible. In October, state regulators proposed new rules that would further restrict which pesticides can be used to grow marijuana to those that are least harmful and already are allowed on crops intended for human consumption and tobacco.

So that’s how Colorado is coming up with its can-use and can’t-use lists. And below are the five most common state-banned pesticides seen in the marijuana recalls issued by Denver’s Department of Environmental Health in 2015 — and what pesticide experts know about them:

Myclobutanil: Fungicide. Active ingredient in Eagle 20 pesticide brand. Considered “slightly hazardous” by the World Health Organization, a “Bad Actor” by the Pesticide Action Network and its own label warns of nervous system problems and toxic fumes.

Imidacloprid: Insecticide. Found in Merit and Mallet pesticide brands. Considered “moderately hazardous” by the WHO, and the National Pesticide Information Center says it’s moderately toxic if ingested or inhaled.

Abamectin and the avermectin chemical family: Insecticide. Found in Avid and Lucid pesticide brands. PAN lists avermectin as a “Bad Actor,” and Avid labels say it’s “harmful if inhaled.”

Etoxazole: Insecticide. Found in TetraSan 5 WDG pesticide brand, which is primarily used on ornamental and landscape plants.

Spiromesifen: Insecticide. Found in Oberon, Judo and Forbid brand pesticides.

Get more information about pesticides that can be used on marijuana at the Colorado Department of Agriculture.