Pesticide Use in Cannabis Cultivation Threatens California Spotted Owls

Recreational cannabis was legalized in California in November 2016. Although 17 other states have legalized recreational marijuana to date, California leads in the amount of cannabis produced, with about 60% of the cannabis grown in the US coming from the Golden State.

Widespread cannabis cultivation can lead to numerous environmental impacts, including groundwater and surface water depletion, soil erosion, habitat loss and fragmentation, and pesticide pollution. In this article, we focus on a secondary impact of cannabis cultivation—the poisoning of endangered and threatened species.

Cannabis and Environmental Regulation

The harmful effects of pesticide exposure in cannabis cultivation are augmented by its historically illicit nature. Since cannabis is still federally illegal, the United States Environmental Protection Agency (EPA) does not recognize it as a crop and has no approved pesticide products specifically designated for cannabis. 

The State of California Department of Pesticide Regulation (DPR) only permits the application of biorational pesticides – relatively non-toxic and low in environmental impact – like citronella and food-grade essential oils.

Trespass grows – illegal cannabis growing sites on private or public land – have a well-documented history of using illicit pesticide substances. Unregulated pesticide use is extremely harmful for wildlife, especially in ecologically sensitive areas. Illegal cannabis growing operations tend to exist near upper watershed streams and in remote forests. California’s remote forests are the habitat of California Spotted Owls (Strix occidentalis occidentalis), a declining wildlife species which provides important ecosystem services.

Anticoagulant rodenticides (ARs) are used to prevent damage to plants and irrigation equipment from rodent pest populations. ARs kill rodents by inhibiting vitamin K synthesis, which delays coagulation and leads to hemorrhaging and death. Through secondary exposure, ARs can kill nontarget wildlife species that prey on rodents – like owls. 

Dusky-footed woodrats, a main food source for Northern Spotted Owls, eat cannabis plant material and use the stalks to build nests. One study found AR compounds in 70% of Northern Spotted Owl carcasses found on remote forested lands.

The Northern Spotted Owl (Strix occidentalis caurina) is a federally listed endangered species and a close relative of the California Spotted Owl, a California Department of Fish and Wildlife (CDFW) species of special concern. California Spotted Owls can be found right here in Nevada County. Owls provide natural pest control by preying on rodents and vermin.

Unfortunately, California Spotted Owl populations are declining, partially due to AR contamination mortalities. A 2019 United States Fish and Wildlife Service assessment of California Spotted Owls discovered severe population declines in 4 out of 5 of their study areas.

Despite their findings, the Wildlife Service failed to list the California Spotted Owl as endangered or threatened under The Endangered Species Act. For more information about this decision, please visit the Sierra Forest Legacy website.

If you’re concerned about pesticides, please support SYRCL’s Growing Green for the Yuba initiative, which encourages cannabis cultivators to adopt watershed-friendly practices for the health of our land, community, and the California Spotted Owls who live here, by getting involved or donating.