Pest management for medical cannabis crops in Canada

Understanding what pesticide and pest management options are for Canada's regulated, commercial medical cannabis producers.

The legalization of medical cannabis has come with the need to reform and even create many policies and regulations in order to provide a safe framework for its production and consumption. One important issue up for contention is the use of pesticides on cannabis plants.

The word pesticide is inherently scary sounding. The suffix -cide invokes death as in genocide or homicide. However unfortunate this may be, pesticides are an integral part of the agriculture industry. In general, pesticides or pest control products are chemical or biological agents that discourage the presence of fungi or insects and stop them from destroying the plant and spreading disease.

According to Tom Ulanowski, quality assurance manager at Canna Farms Ltd., “a large and important part of cannabis cultivation is pest control, which ensures optimum plant health throughout the lifetime of the crop.” Pesticide use is regulated by the Health Canada Pest Management Regulatory Agency (PMRA) in accordance to the Pest Control Products Act (PCPA). This governing body examines peer-reviewed scientific research in order to establish appropriate guidelines for use of the pesticides and maximum residue limit (MRL) so as to not pose any health concerns in humans.

Cannabis is currently regulated under the Marihuana for Medical Purposes Regulations (MMPR) where there are stipulations regarding the use of registered pest control products under the PCPA. Cannabis plants are not to be treated at any stage of growth with a pest control product that has not been registered under the PCPA. Microbial and chemical residuals must be within generally accepted levels for human consumption as established by various international publications including the U.S. Pharmacopoeia and the European Pharmacopoeia.

A previous version of the MMPR stipulated under section 54 that an MRL must be adhered to for pest control products under the PCPA. A later redaction removed this stipulation, as none of the approved pesticides for cannabis use have an established MRL as set by the PMRA. These products are in fact considered safe as no significant adverse effects have been reported in toxicity and pathogenicity studies as reviewed by the PMRA.

There are currently 10 registered brands of pesticides approved for use on cannabis. Many consist of the same active ingredients and as such there are only 13 registered pesticides with unique active ingredients.

 Bioprotec CAF

Larva, Lepidoptera, Worm, Armyworm, Soy
Larva, Lepidoptera on a Soy leaf. Image via Pixbay
  • Aqueous biological insecticide
  • Active ingredient: Bacillus thuringiensis strain EVB113-19
  • Selectively toxic to some species of lepidopteran larvae
  • Treats cabbage looper pest in Cannabis
  • Pre-harvest interval (PHI; time between last application and harvest) of 0 days
  • Poses little threat to human health
  • Biodegrades quickly in the environment

RootShield HC

  • Biological fungicide wettable powder
  • Active ingredient: Trichoderma harzianum Rifai strain KRL-AG2
  • Suppression of root or foliar diseases
  • Protects roots against Pythium, Rhizoctonia and Fusarium
  • Suppresses gray mold (Botrytis cinerea) in foliage
  • No signs of toxicity or pathogenicity in rats via oral or intravenous routes

Actinovate SP

  • Biological fungicide soluble powder
  • Active ingredient: Streptomyces lydicus strain WYEC 108
  • Suppression of powdery mildew (Sphaerotheca macularis) and gray mold (Botrytis cinerea)
  • Commonly found in soil
  • No adverse health effects have been attributed to dietary exposure in humans

Botanigard ES Whitefly

  • Emulsifiable Suspension Mycoinsecticide
  • Active ingredient: Beauveria bassiana strain GHA
  • Control of whiteflies, aphids and thrips in Cannabis
  • PHI of 0 days
  • Dietary and environmental risks are not of concern

Neudosan Commercial/Opal/KOPA Insecticidal Soap

  • Insecticidal soap
  • Active ingredient: Potassium salts of fatty acids
  • For control of aphids, spider mites and whiteflies in Cannabis
  • PHI of 0 days
  • Soap salts
  • Used as multi-purpose food additives classified by FDA as generally recognized as safe
  • Very low toxicity when ingested or exposed to skin
  • High doses in humans may cause stomach upset and vomiting in humans
powdery mildew
powdery mildew

MilStop 

  • Foliar fungicide
  • Active ingredient: Potassium bicarbonate
  • Suppression of powdery mildew
  • PHI of 0 days
  • No evidence of human carcinogenicity or adverse effects of overexposure
  • Food additive generally recognized as safe

Agrotek

  • Vaporized sulphur powder
  • Active ingredient: Sulphur
  • Control of powdery mildew (Sphaerotheca macularis)

Botanigard 22 WP 

  • Same active ingredient (Beauvaria bassiana) as previous product (Botanigard ES) except instead of an emulsifiable suspension, this rendition comes in a wettable powder format.

Rootshield WP

  • Updated version of Rootshield HC. Same active ingredient (Trichoderma harzianum Rifai strain KRL-AG2). New product offers easier mixing and 0 hour REI (restricted-entry interval) compared to 4 hours for Rootshield HC.

Vegol Crop Oil 

  • The active ingredient is canola oil.
  • Controls a variety of insects and mites and suppresses powdery mildew growth.
  • Canola oil can act as an insecticide through the act of suffocation and as a fungicide by creating a physical barrier preventing the plant infection by fungi.
  • Health risks from residues are of low concern since canola oil is of low toxicity and has a long history of dietary use.

Bioprotec Plus 

  • Higher concentration of the active ingredient Bacillus thuringiensis subspecies kurstaki, strain EVB113-19 compared to Bioprotec CAF.
  • 14.60% active ingredient compared to a minimum of 8.12% in Bioprotec CAF. 

Health Canada’s PMRA registers a pesticide only after it is scientifically reviewed and found to be both effective and safe for use with minimal risk to human health and the environment. Bioprotec CAF for example, contains Bacillus thuringiensis strain EVB113-19 as the active ingredient and is only active under alkaline conditions found in certain insects’ digestive systems and therefore the acidic stomachs of humans and animals cannot activate this toxin. Studies have shown that even if the spores are ingested or inhaled, they are eliminated without any adverse health effects. A full report can be found for each of the strains on Health Canada’s website (links at the bottom).

Detection methods generally depend on the nature of the pesticides and follow published protocols from the U.S. or European Pharmacopoeias. For bio-pesticides or microbial pest control agents that contain microorganisms as active ingredients, isozyme analysis is used to evaluate the starter cultures prior to production. Isozymes are enzymes that catalyze the same reaction but contain different amino acid sequences. For example, the particular strain of Trichoderma used in RootShield is differentiated by comparing 17 isozyme patterns to known profiles. This is accomplished using a gel electrophoresis technique.

Another method used to differentiate various strains of microorganisms is by observing the morphology of the colonies when grown on a selective medium. Strain specific identification can also be achieved by DNA fingerprinting methods. In some cases, strain specific DNA probes are available and can be used to amplify a specific region of a DNA strand through a process known as polymerase chain reaction or PCR. Microbial pest control agents approved for use on cannabis by the PMRA show no adverse effects in toxicity and pathogenicity studies and there are no data available to suggest they are capable of producing any secondary metabolites of potential health concern. As a result, no methods are needed to quantify residues in the plant.

Other pesticides approved for use on cannabis include potassium salts of fatty acids, potassium bicarbonate and sulphur. They have all shown no evidence of adverse effects in humans and produce residues not expected to exceed levels that occur naturally or levels found in foods. These pesticides therefore also do not require a set MRL. The presence of these compounds can be identified and quantified using either gas-chromatograph (GC) or high performance liquid chromatography (HPLC) methods.

In the event of non-compliance, Health Canada requires the destruction of the cannabis plants or dried cannabis and a full recall may be ordered if the product has already been sold. Depending on the severity of the offence, enforcement measures can stem from verbal education and enforcement letters to suspension of their MMPR license, monetary penalty of up to $4000 and even prosecution. Licensed producers are inspected on a regular basis and are audited for records of cannabis produced and approved for sale.

The likelihood of Health Canada uncovering illegal use of pesticide is “quite high” according to Ulanowski. “All Licensed Producers are required to keep retention samples of any cannabis sold for at least one year after the final date of sale, and documents related to the lot for a minimum of two years.

Similarly, security camera footage must be kept for a minimum of 2 years. In the event Health Canada inspectors suspect illegal use of pesticides, they can commission independent testing to be done by analytical laboratories where GC and HPLC is employed to test for THC and CBD levels as well as an exhaustive list of 150 known pesticides not regulated for use on cannabis. This is all done in accordance with U.S. Pharmacopeial Convention. According to Tom, the stringent testing combined with penalties is believed to be enough to deter producers from using unapproved pesticides, “I suspect that risking loss of their highly-coveted MMPR License, or perhaps negative press, is enough to prevent the vast majority from even thinking about doing so.”

Canna Farms Ltd. ensures compliance with Health Canada by using predatory bugs such as Orius insidiosus “which aggressively hunts for pests like thrips, spider mites, insect eggs, and aphids.” These biocontrols have a slower response time compared to chemical pesticides, but they are very effective. Says Ulanowski “the use of biocontrols, combined with strict sanitation protocols and environmental monitoring/control, ensures our grow rooms remain free of any pest-related issues.” 

This article has been updated to note new approved pesticides.


Bacillus thuringiensis strain EVB113-19: http://www.hc-sc.gc.ca/cps-spc/alt_formats/pdf/pubs/pest/_fact-fiche/btk-eng.pdf

Trichoderma harzianum Rifai strain KRL-AG2: http://publications.gc.ca/collections/Collection/H113-7-2002-1E.pdf

Streptomyces lydicus strain WYEC 108: http://publications.gc.ca/collections/collection_2007/pmra-arla/H113-9-2007-10E.pdf

Beauveria bassiana strain GHA: http://publications.gc.ca/collections/collection_2010/arla-pmra/H113-9-2009-3-eng.pdf

Potassium salts of fatty acids: http://npic.orst.edu/factsheets/psfagen.pdf

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