Pesticides: Their Role in Medical Cannabis Cultivation


Pesticides and insecticides have featured prominently in the national and Maryland local news lately, and the general public has taken notice. One recent news story focused on claims that consumer beverage company LaCroix used an insecticide to flavor beverages. The alleged insecticide is linalool, one of the substances that gives lavender its smell and one of the many naturally occurring terpenes found in cannabis. While linalool can function as an insecticide, it is also being studied for its efficacy in treating a number of serious medical conditions, including Alzheimer’s disease. Other recent stories investigated the case of a Maryland medical cannabis cultivator that has been placed on probation by the Maryland Medical Cannabis Commission (MMCC) for allegations that the company used pesticides on its crop.

However, headlines often leave out some very important details, especially when they pertain to scientific topics. Pesticides, which are regulated by the Environmental Protection Agency (EPA), cover a broad range of compounds and have varying degrees of safety. The EPA requires that all pesticides be registered (except 25(b), more on that below) and that extensive studies be conducted to investigate environmental impact and health effects for both handlers and consumers of products impacted. Once approved, these pesticides must have labels that specify how they may be used. The EPA periodically reviews the registrations in order to consider new information for a particular active ingredient. While there is a misperception that all pesticides and insecticides are harsh, toxic chemicals, the reality is that—similar to the LaCroix linalool case—pesticides and insecticides can simply be defined as “any agent that can control or eliminate pests or insects.” From harsh agents that require protective gear and routine safety monitoring to protect against toxicity to harmless substances, a pesticide is just something that controls pests.

In May of this year, Maryland Governor Hogan signed House Bill 2 into law, which in part allowed for the use of crop protection agents, another name for pesticides, in the cultivation of medical cannabis. This inclusion has been a cause for concern for some. The crop protection agents included in the language of House Bill 2 fall under three categories of pesticides. The first category is “EPA-exempted from registration”. Also referred to as “minimum risk pesticides” or “25(b)”, these compounds must meet specific conditions outlined by the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and have been determined to pose little to no risk to human health. Some examples of pesticides on the 25(b) list include cinnamon, white pepper, and potassium sorbate. The Maryland Department of Agriculture (MDA) has not approved any 25(b) pesticides for use on medical cannabis to date. Bonide Mite X Ready to Use is a 25(b) insecticide approved by the MDA for use on medical cannabis. The active ingredients are Cottonseed Oil, Clove Oil, and Garlic Oil.

The second category is “exempt from tolerance”, a category that applies to pesticides which, after extensive independent research and when used according to specific guidelines, have been determined not to pose health risks. Here, tolerance refers to the allowed amount of pesticide residue that could remain on a crop. Given the minimal health risk of these agents, the EPA does not require these residues to be monitored. It is important to note that the pesticide must be used as stated on the label, which helps to limit the potential exposure. An example of these types of pesticides permitted by MDA for use on cannabis are specific products based on neem oil, an extract of Indian lilac seeds.

The third category of pesticides included in the bill are agents that are permitted for use in organic agriculture. The U.S. Department of Agriculture determines which pesticides are suitable for use on certified organic products. An example of an organic pesticide permitted by MDA uses mineral oil as the active ingredient.

Another point to consider is pesticide half-life. The half-life is the time it takes for half of the ingredient to degrade, and generally continues at the same rate over time. The half-life of neem oil on plants, for example, is 24 to 60 hours. Over eight half-lives, or approximately 3 weeks, it could be expected that less than 1% of the ingredient would remain on the plant. The dry and cure process for cannabis is many weeks, at which point an ingredient with a short half-life, would have dissipated to undetectable levels. Often, pesticides are applied early in the plant’s life, meaning that several months may pass before it is ready for sale.

There are two things to keep in mind with all of this. One is that the pesticides in the bill are not automatically permitted but must be reviewed and approved for use on cannabis. The other is that MDA is working closely with the MMCC to identify suitable pesticides.

The key here is that, just as we know that linalool can serve dual functions as an insecticide and a potential medicine, many other compounds we encounter in our daily lives can be used as pesticides in cannabis cultivation. Indeed, many compounds that have pesticide effects can be used safely and without exposing consumers to undue side effects. And of course, from a scientific perspective, more study is warranted for all of these agents.

Shannon Hoffman is Regional Director of Operations and Certifying Chemist at Steep Hill.

Previous articleAdvocating for the Science Behind Medical Cannabis: Interview with Josh Crossney
Next articleAn Absolute Lifesaver