Agriculture is a bug-filled industry that must put in work to remain clean. Soil fumigants are a major controversy in this regard. But, with outdoor cannabis cultivation license approvals now on the rise, Health Canada‘s Pesticide Management Regulatory Agency (PMRA) approved a fumigant for cannabis farms – chloropicrin (trichloronitromethane.)

Two fumigants are approved for Canada’s outdoor cannabis crops and are produced by Triest Ag Group Inc.

  • Chloropicrin 100 Liquid Soil Fumigant – 99% Chloropicrin
  • Pic Plus Fumigant – 85.1% Chloropicrin

Despite the PMRA’s recent approval of chloropicrin for cannabis farms, the fumigant is banned in other countries. The reason for its prohibited status in the EU, for example, is due to its risk for pulmonary injury alongside its environmental toxicity. (1) So, North America still appears to be opposing other countries that banned chloropicrin, which is in parallel with a study published in Biomed Central. (2) Therefore, certain American farmers avoid chloropicrin, sometimes preferring methyl bromide but that was phased out by the EPA. (3.)

Thankfully though, the two fumigants approved by Canada’s PMRA are injected into the soil strictly before any cannabis is planted on the farm. Chloropicrin can, however, still become trapped in the earth and can lead to respiratory damage. (4) This fumigant, specifically, caused over 1000 pesticide-related illnesses from 2000 to 2015 in California alone. (2)

The fumigant approved for cannabis farms, chloropicrin, can be applied by drip lines.
Photo courtesy of UC Davis.

Is soil better dead or alive for crops?

Chloropicrin can be used as a fumigant on cannabis farms to kill soil pathogens. Gassing the soil is simple and cost-efficient. Moreover, avoiding the hazards of chloropicrin is far less tedious compared to utilizing healthy soil microbes in the farm’s favour. And, this particular fumigant can help promote a healthy soil microbe known as Trichoderma spp. (5) So, there is a major cost advantage with chloropicrin.

This fumigant is most effective for soil diseases but it is not effective for nematodes or invasive plants. (6)

In contrast, cannabis connoisseurs and some of the more skilled cultivators prefer a soil bed that is very much alive, brimming with life. Living soil produces far better crops than dead dirt but the cost is far greater; then again, so is the reward. This is why good growers know how to tame the bugs in their plants and the first lesson occurs in the ground. Compost teas keep a soil bed active and healthy, but this completely opposes the practice of soil fumigation.

Living versus sterilized growing mediums

Not all producers are brazen enough to try and keep living soil beds since fumigants can provide crop protection at much lower costs. The question is, will lower-priced legal flower compete with high-quality black market cannabis if the former is fumigated? Perhaps, some will find success with chloropicrin. Admittedly, the cannabis industry is familiar with sterilized soil and hydroponic mediums, just not large outdoor farms that utilize an approved fumigant.  

So, it is hard to say if this practice will be drafted into any company’s Integrated Pest Management (IPM) plans. However, cheap weed does tend to tantalize. Convenience, but also viability is a good reason for farmers to ignore outspoken concerns from consumers, craft growers, and the planet. But can chloropicrin be considered the lesser of two evils in the face of harmful bacteria and other pests for the sake of financial viability?

Shank Injection of a soil fumigant. Photo courtesy of UC Davis.

Does Chloropicrin affect your lungs?

Only approved fumigation specialists can apply chloropicrin due to safety precautions. However, exposure to four parts-per-million of chloropicrin for a few short seconds can lead to some amount of incapacitation. And beyond this, very interim exposure to fifteen parts-per-million can cause respiratory tract injury. So, illness events have undoubtedly occurred due to the use of chloropicrin despite safety parameters. (7)

Unfortunately, it is unknown if chronic exposure to chloropicrin can cause developmental or reproductive damage according to the CDC. However, the fumigant is severely toxic to fish and birds and harmful to bees. This is why the soil must be covered with special plastic for at least ten days after a farm uses this fumigant before planting cannabis. (8)

Is chloropicrin sustainable compared to living soil?

In general, there is a lot of interest in moving away from soil fumigation and more towards sustainable practices according to releases in MDPI and Hindawi. (9, 10) Furthermore, a study conducted by the Institute of Plant Protection and the Chinese Academy of Agricultural Sciences in Beijing, China used PCR sequencing to detect the impact chloropicrin has on the soil. (11)

This test can measure life forms in any medium by detecting bits of DNA or RNA. Based on this study, chloropicrin has a significant negative impact on soil health surrounding the fumigation site. (12) Moreover, any negative impact caused by fumigants will be magnified in cannabis sales.

An alternative beyond living soil is to cover the ground with plastic and let the sun effectively cook the bad bugs in the dirt. This method is known as solarization and a similar technique is used to remediate soil contaminated with cadmium.

Let us know your thoughts now that a fumigant has been approved for cannabis farms in the comments. Do you prefer cannabis grown from dead or living soils? And stay for details on more pesticides approved for cannabis cultivation next week.

Title photo courtesy of the Government of Western Australia.


  1. European Food Safety Authority (EFSA), Anastassiadou, M., Arena, M., Auteri, D., Brancato, A., Bura, L., Carrasco Cabrera, L., Chaideftou, E., Chiusolo, A., Court Marques, D., Crivellente, F., De Lentdecker, C., Egsmose, M., Fait, G., Greco, L., Ippolito, A., Istace, F., Jarrah, S., Kardassi, D., Leuschner, R., … Villamar-Bouza, L. (2020). Peer review of the pesticide risk assessment of the active substance chloropicrin. EFSA journal. European Food Safety Authority18(3), e06028. doi/10.2903/j.efsa.2020.6028 
  2. Donley, N. The USA lags behind other agricultural nations in banning harmful pesticides. Environ Health 18, 44 (2019). doi/10.1186/s12940-019-0488-0
  3. Norman C. S. (2005). Potential impacts of imposing methyl bromide phaseout on US strawberry growers: a case study of a nomination for a critical use exemption under the Montreal Protocol. Journal of environmental management75(2), 167–176.
  4. Pesonen, M., Häkkinen, M., Rilla, K., Juvonen, R., Kuitunen, T., Pasanen, M., & Vähäkangas, K. (2014). Chloropicrin-induced toxic responses in human lung epithelial cells. Toxicology letters226(2), 236–244. doi/10.1016/j.toxlet.2014.02.006
  5. De los Santos, Berta & Barrau, Carmen & Arroyo, Francisco & Porras, Marcelo & Medina-M’inguez, Juan. (2003). Relationship between Trichoderma Soil Populations and Strawberry Fruit Production in Previously Fumigated Soils. HortScience: a publication of the American Society for Horticultural Science. 38. 10.21273/HORTSCI.38.7.1400.
  6. Sande, D., Mullen, J., Wetzstein, M., & Houston, J. (2011). Environmental impacts from pesticide use: a case study of soil fumigation in Florida tomato production. International journal of environmental research and public health8(12), 4649–4661. doi/10.3390/ijerph8124649
  7. Oriel, M., Edmiston, S., Beauvais, S., Barry, T., & O’Malley, M. (2009). Illnesses associated with chloropicrin use in California agriculture, 1992-2003. Reviews of environmental contamination and toxicology200, 1–31. doi/10.1007/978-1-4419-0028-9_1
  8. Ajwa H, Stanghellini M, Gao S, Sullivan D, Khan A, Ntow W, Qin R. 2013. Fumigant emission reductions with TIF warrant regulatory changes. Calif Agr 67(3):147-152. doi/10.3733/ca.v067n03p147.
  9. Hanschen, F.S.; Winkelmann, T. Biofumigation for Fighting Replant Disease- A Review. Agronomy 202010, 425. doi/10.3390/agronomy10030425
  10. Laura Ney, Dorcas Franklin, Kishan Mahmud, Miguel Cabrera, Dennis Hancock, Mussie Habteselassie, Quint Newcomer, Brendan Fatzinger, “Rebuilding Soil Ecosystems for Improved Productivity in Biosolarized Soils”, International Journal of Agronomy, vol. 2019, Article ID 5827585, 10 pages, 2019. doi/10.1155/2019/5827585
  11. Li, J., Huang, B., Wang, Q., Li, Y., Fang, W., Yan, D., Guo, M., & Cao, A. (2017). Effect of fumigation with chloropicrin on soil bacterial communities and genes encoding key enzymes involved in nitrogen cycling. Environmental pollution (Barking, Essex : 1987)227, 534–542. doi/10.1016/j.envpol.2017.03.076
  12. Zhang, S., Liu, X., Jiang, Q., Shen, G., & Ding, W. (2017). Legacy effects of continuous chloropicrin-fumigation for 3-years on soil microbial community composition and metabolic activity. AMB Express7(1), 178. doi/10.1186/s13568-017-0475-1
  13. US20180243786A1