The Potential of Biocontrol in Cannabis

Robert Starnes, University of California Davis
Robert Starnes, University of California Davis

The accelerating legalization of cannabis around the U.S. is providing new opportunity in the form of an alternative crop, and just as much uncertainty about what kind of crop protection can be used to grow it. We asked Robert Starnes, Senior Superintendent of Agriculture at the University of California, Davis (UC Davis) in the Department of Entomology and President of Shale Peak Horticulture, for his thoughts on where biocontrol fits for cannabis growers.

Q: What’s the current situation with available pest control materials in cannabis crops?
Starnes: Cannabis is in a gray area regarding chemical pest management in states where it is legal as a medicinal or recreational crop. As growers receive state and/or county permits to grow cannabis, they must also register with their county ag commissioners. Many growers don’t realize all the rules and regulations that accompany this. In California, spray applicators need a Qualified Applicator License/Qualified Applicator Certification from the Department of Pesticide Regulation. Any grower spraying a commercial crop with a registered insecticide, biopesticide, fungicide, or herbicide must have one of these licenses. Growers must also submit a monthly use report, where inappropriate pesticides would be questioned.

There are, however, a few exceptions in California. Cannabis growers are allowed to spray pesticides that contain an active ingredient exempt from residue-tolerance requirements, and are registered and labeled for a use that is broad enough to include use on cannabis (unspecified green plants) or exempt from registration requirements as a minimum risk pesticide under FIFRA.

Q: Why are biocontrols important tools to add to that mix?
Starnes: The best pest management option for cannabis is biological control. Using predatory mites and insects to control pests doesn’t require permits or monthly use reporting. Also, insects will never develop resistance to being eaten or parasitized.

Spraying a plant with any pesticide or biopesticide will leave a residue, and it’s becoming common practice to test the final cannabis product for residues. If these products test positive they can be rejected from dispensaries. Some dispensaries set their own rules for residues, but the government may soon regulate which products are acceptable. Even if a product is generally regarded as safe but banned in cannabis use, residues will be discovered and the product rejected for sale. Biocontrol leaves no residue and isn’t regulated in terms of final sale.

Our strategy at Shale Peak Horticulture is to design a preventative biocontrol release program to build a standing army of predators. We feed our predatory mites an artificial diet of Ephestia sp. eggs mixed with Artemia sp. cysts (eggs) in the cannabis crop. This keeps the predatory mites in the crop, ready for the pests to arrive.

Q: What’s the current legal status of biopesticides with regard to use in cannabis crops?
Starnes: It is the same as conventional pesticides for cannabis use: there are no registered products specifically for use directly on cannabis. Some states have a list of legal products they allow, while most haven’t produced much information for cannabis growers. Basically, all registered pesticides and biopesticides are illegal to use on cannabis unless exempted by your state. Your state regulations can be found easily online.

Q: How can cannabis growers learn to use biocontrols?
Starnes: Work with your county ag commissioner. They can help you understand which products are legal or illegal to use.

Integrated Pest Management is a complex system. Seek out a biocontrol specialist for advice and help on understanding which organisms will work in your location. Some biocontrols work better at higher temperatures, others at lower temperatures. The same applies to relative humidity. Most biocontrol companies have staff to advise you on which products to use based on the pest pressure you’re experiencing. There are also consultants you can hire to help scout your crop for pests and make recommendations on which biocontrol agent will work for you.

Robert Starnes (bob@sphort.com) is a Senior Superintendent of Agriculture at UC Davis in the Department of Entomology, where he conducts research on integrated pest management and remote sensing in agriculture, and President of Shale Peak Horticulture, which offers biocontrol pest management solutions to cannabis growers.