As most of us know, pesticides are commonly used in the agricultural production of most consumable crops, whether it be vegetables, fruits, hops, tobacco, or Cannabis. In Oregon, Cannabis producers must have all Cannabis flower and extracts tested for a panel of approximately 60 pesticides, each pesticide with its own “action limit.” If a test reveals that the material contains a pesticide over the action limit, it is said to have “failed” and is arranged for either retesting or destruction.
In light of growing pesticide concerns in other states where Cannabis is legal such as Washington and Colorado, Oregon adopted a fairly rigorous pesticide testing law which only recently went into effect on October 1 of 2016. This change in testing requirements has been alarming to some organic Cannabis cultivators that are finding that batches are now testing positive for components of some OMRI approved pesticides, such as Spinosad, whereas these pesticides were not typically tested for in prior years.
So What Pesticides Are Good To Use On Cannabis?
It could be argued that a goal of cultivation should be to minimize or entirely eliminate pesticide use through well structured integrated pest management plans. However, many cultivators still value pesticides, whether organic or not, as an essential tool in their arsenal for ensuring a successful harvest.The question then becomes, “So what pesticides are good to use?”
Ultimately this is a question that cannot be answered by anyone but the cultivator, but there are a number of factors to consider when evaluating pesticides for use. Most Cannabis testing laboratories do not have a certified toxicologist on staff to answer questions about the potential health effects of pesticides, and it would generally be ethically and legally irresponsible for a company to make any claims about the suitability of pesticide use in the first place. Instead, cultivators are left with two options: avoid pesticide use altogether or perform independent research to make informed decisions about what products to use and when to apply them.
So let’s assume you plan to use pesticides and you are ready to do your research. What should you be looking for?
Assuming that researching the toxicity of a product you intend to use is a given, one of the first characteristics of a pesticide that a cultivator should understand is the pesticide’s mobility, or the likelihood that it will move from the site of application. This is primarily related to water solubility, because if the pesticide is soluble in water, it will mix with rain and irrigation applications and subsequently travel with the water run-off. To avoid unintentional non-point pollution, pesticides with a low mobility rating should be used.
The second characteristic to take note of is pesticide persistence, which is a measure of how resilient the compound is to breaking down when exposed to water, light, and oxygen. The reason that the use of the pesticide DDT became so alarming in the 1970s is that it was found to have an extremely high persistence rating, taking years and in some cases decades to breakdown to non-detectable levels in an environment where it was applied.
After the 1980s or so, there became a focus on producing pesticides that had a very low persistence to combat large-scale environmental pollution. Today many of the common pesticides available in stores have relatively low persistence ratings. However there is little information about whether these low persistence compounds actually break down quickly into nontoxic components, or whether they simply oxidize or otherwise convert to some other compound with a greater persistence and potentially a similar toxicity rating than the original pesticide compound.
Different Modes of Action: Contact, Translaminar, and Systemic
Beyond pesticide mobility and persistence, not all pesticides have the same method of action. The differences in a compounds method of action will affect whether or not the pesticide will leave residues long after its application. Some pesticides kill insects directly upon contact, while some pesticides soak into leaf tissues, while others still are absorbed and circulated throughout the plant for very long periods of time to ensure action against any insect that happens to nibble on the plant.
Pesticides that kill insects directly upon contact are called, aptly enough, Contact Pesticides. Examples of common contact pesticides include things like Bifenazate, Bifenthrin, Carbaryl, and Pyrethrins. These pesticides often have low persistence ratings (though not always) and are thought to degrade quickly. The activity of contact pesticides is sometimes extended, though, by the addition of synergistic compounds like piperonyl butoxide. If a synergist is present alongside a contact pesticide, it is safe to assume that the persistence of that compound will be longer than if the compound were applied by itself.
Translaminar Pesticides, on the other hand, will soak into leaf tissues forming a reservoir of pesticides that linger within the tissue. Common examples of translaminar pesticides used in the Cannabis industry are things like Spinosad, Chlorfenapyr, Abamectin, and Acephate. These types of pesticides present particular problems for leafy parts of the Cannabis plant, like “trim”, which is commonly used to produce extracts and other Cannabis products.
Theoretically the chances of failing a pesticide test for translaminar pesticides may be reduced by removing as much leafy material as possible from the final product. Translaminar pesticides present unique health risks to consumers that juice raw Cannabis leaves.
Some of the most long lasting pesticides in a plant are Systemic Pesticides, which actually get absorbed into the plant’s vascular system and become recirculated throughout the plant repeatedly for up to months after application. Common systemic pesticides used in the Cannabis industry are things like Imidacloprid, Azadirachtin, and Myclobutanil, a commonly used fungicide.
Because these pesticides will linger in the plant for very long periods of time, care must be especially taken to the time of application when using these pesticides. If desiring to use a systemic pesticide in an application regime, it may be worthwhile to partner with a testing lab for a series of research and development experiments to determine how long the compounds tend to linger
There are a variety of excellent resources available for free on the web for learning more about any particular pesticide product you may be considering. I highly recommend first checking out the Pesticide Properties Database (http://sitem.herts.ac.uk/aeru/ppdb/en/) and the BioPesticide Properties Database (http://sitem.herts.ac.uk/aeru/bpdb/index.htm) as well as looking up the unique Material Safety Data Sheet for any product you may be using. To do this, just simply navigate to your favorite web search engine and type the name of your product followed by “MSDS” or “Material Safety Data Sheet”. This will tell you the listed active ingredients that the manufacturer is required to reveal. However, keep in mind, that it may be possible to have unlisted active ingredients in a product as well. Some pesticide laboratories may be willing to test a particular pesticide product for unlisted ingredients if you request it.
Interested in learning how to cultivate crops without the use of pesticides? It ultimately boils down to properly managing the ecology of your cultivation site through proper soil management, use of cover crops and companion plants, and managing the biodiversity of the cultivation area. There are a variety of sustainable cultivation certifications available to Cannabis cultivators. As well there are a number of cultivators currently exhibiting "eco-dynamic" methods of cultivation, setting examples of how Cannabis can be grown with the use of minimal inputs and no chemical pesticides.
A great place to begin learning about sustainable or regenerative cultivation techniques is the Natural Resource Conservation Service’s article about the soil food web written by renowned soil biologist, Dr. Elaine Ingham (https://www.nrcs.usda.gov/wps/portal/nrcs/detailfull/soils/health/biology/?cid=nrcs142p2_053868).
Learn more about integrated pest management by visiting the EPA’s website. (https://www.epa.gov/managing-pests-schools/introduction-integrated-pest-management)
Have another resource you have found helpful in performing your own research? Please share and let us know!
Jason Wilson, MS
Chief Quality Officer and Technologist