Timothy Leach, partner, TechnIEQ, LLC

There are several potential opportunities for manufacturers of UV LED devices specifically targeting improved crop yield, product quality and product safety within the cannabis industry. To better identify these potential applications, one needs to understand what negatively impacts agricultural crops in general and cannabis crops specifically. Mold and bacteria attack and destroy plants and, in many cases, decimate entire crops. Microorganisms cause more crop loss than all other organisms combined.2 It is estimated there are more than 8,000 species of mold that affect plants.3

Cannabis crops are highly susceptible to damage caused by microorganisms. The most common losses are attributed to mold, with the most problematic species being Botrytis cinerea or “gray mold” and Sphaerotheca macularis or “powdery mildew.” Agricultural practices have historically used fungicides, such as demethlation inhibitors (DMI) and sterolbiosynthesis inhibiting (SI), to protect crops from pathogenic mold.

The negative impact from the use of chemicals, in addition to extra costs, can include plant stress, pathogen resistance to chemical treatments and interference with biocontrol of diseases that are kept in check by naturally occurring microflora. More importantly, they are not eco-friendly. There is a movement within the cannabis growing industry to develop more sustainable and eco-friendly agricultural practices, with the intention of becoming chemical-free. The combination of these two driving factors lends itself to potentially large market opportunities for UV LED device manufacturers who can fulfill both needs.

To design and apply successful and predictable solutions, suppliers need to become intimate with the cannabis growing process. Identifying solutions to the previously stated issues confronting cannabis growers should come from a systemic understanding. In his seminal work, The Fifth Discipline: The Art and Practice of the Learning Organization,1 renowned systems scientist Dr. Peter Senge discusses and explains the concepts of systems thinking. Senge states that too often people try to solve complex issues or problems in a linear fashion. This type of thinking often leads to seeking panaceas that rarely end with successful solutions. He goes on to explain that problems or issues are really made up of loops or circles that contain variables with cause and effect relationships.

Over the past number of years, this systemic thought process has been adopted and applied by organizations and institutions to find solutions to complex issues.

break-the-chain-of-infection-ad
Image 1. This infographic shows the chain of infection. Image courtesy of APIC.

A good example is the healthcare profession trying to better understand sources and modes of transmission of hospital-acquired infections (HAIs). Years of in-depth research addressing the variables – including influences from patients, staff, visitors, instruments and environment – led the Association for Professionals in Infection Control and Epidemiology (APIC) to develop what is described as the Chain of Infection (Image 1).17 The chain identifies not only the sources and modes of transmission but also recommended solutions at every critical point.

The principals of systemic thinking that produced the Chain of Infection model for healthcare professionals can be applied to the cannabis-growing industry in dealing with issues of crop yields and product safety. Like HAIs, the greatest risks to crop loss and product safety are mainly caused by pathogenic microorganisms made up of bacteria and mold/fungi.

cannabis-cycle
Image 2. Cannabis cycle from growing room to customer

As suppliers become more aware of the problems confronting the cannabis industry, they start to look at the links in the chain where these microorganisms are introduced. Once the chain is established, protocols and technology can be applied to break the chain of poor yields and unsafe product. For this, there are three points of critical process: the growing room, postharvest drying room and product storage facility (Image 2).

At each critical point in the process the suggested potential solutions are as follows:

1. Growing room

  • UV-C for growing room’s heating, ventilation and air conditioning (HVAC)
  • UV-B for direct exposure to cannabis plants

2. Postharvest cannabis bud
  drying rooms

  • UV-C for drying room’s heating, ventilation and air conditioning (HVAC)
  • UV-C for direct exposure of drying room’s surfaces and drying cannabis buds

3. Finished product storage

  • UV-C for storage room’s heating, ventilation and air conditioning (HVAC)

Growing rooms

cannabis-plants
Image 3. Typical growing room

Climatic conditions within cannabis growing rooms are ideal for the reproduction and spread of pathogenic mold and bacteria (Image 3). The humid conditions found in these environments helps proliferate the growth of pathogens on plants and surfaces. Once a plant becomes infected, the mold will release spores into the air where air movements from the ventilation/air conditioning systems can spread spores to other plants rapidly.

In addition to the spread of spores, the HVAC system further compounds the problem with the development of an internal biofilm that proliferates at the condensate cooling coils and filters. This, in turn, becomes a significant reservoir of mold. If left untreated, the ventilation system will continuously grow mold, spread its spores within the growing room and potentially infect and decimate the entire crop. Many of the microorganisms cultured from the HVAC systems of cannabis growing facilities are threats to their crops (Table 1 and Image 4).

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Table 1. Microorganisms cultured from HVACs at cannabis grow facility
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Image 4. Scanning electronic microscope photo of
microbial contamination

The suggested steps to reduce the growing room microbial pathogens are two-fold. The first deals with treating the air delivered by the room’s HVAC system with UV-C. The application of UV-C in HVAC has become an accepted and cost-effective technology for improving HVAC system hygiene and germicidal air treatment.10, 11, 12, 13, 14, 15, 16 Every UV-C system should be designed to meet the customer’s requirements and built to fit the configuration of the existing HVAC system. The UV-C energy field, or total amount of UV-C energy, is designed specifically

cannabis-HVAC-coils2
Image 5. UV-C treatment of HVAC coils, filters and air. Photo courtesy of Fresh-Aire UV, Inc.

to achieve a desired disinfection level of the HVAC cooling coils, filters and air (Image 5). When utilizing a UV-C system within the HVAC, the air being introduced to and recirculated within the room is continuously being disinfected by the UV-C, thus reducing the numbers and spread of pathogenic microorganisms.

The second suggested step in the growing room is a non-toxic treatment of the cannabis plants with UV-B. UV-B functions in two specific ways to protect plants against infection. The first is a biological response, by the plant, when exposed

cannabis-HVAC-coils
Image 6. UV-C treatment of HVAC coils, filters and air. Image courtesy of AgriCultra.

to UV-B energy. Though it is well understood that plants have a photoreceptor for visible light, a UV-B photoreceptor (UVR-8) only recently has been described at the molecular level (Image 6). The plant’s UV-B photoreceptor is linked to a specific molecular signaling pathway, allowing the plant to acclimate itself to UV-B.

As this happens, the plant cells are constantly adjusting to accommodate changing demands and environmental stresses, including becoming more resistant to infection by pathogens.8 UV-B also has germicidal properties. Studies have demonstrated significant reductions of powdery mildew on tomatoes, roses and grapes5, 6, 7 with short exposures to UV-B during the growing cycle. The short exposures were low enough not to be phytotoxic to the host plant but high enough to be germicidal to powdery mildew.

Postharvest product: Drying rooms and product storage

cannabis-storage2
Image 7. Cannabis buds in drying room baskets and trays

In many cases, cannabis products may not reach the consumer for months or, in some cases, years after harvest. This can lead to yield loss for growers and health issues for the consumer. The microorganisms posing postharvest problems can be categorized into two groups.

Group one is molds, such as gray mold, powdery mildew, cladosporium, fusarium and alternaria. These organisms infect the living plants and remain with the product postharvest.

Group two includes mold such as aspergillus, penicillium, rhizopus and mucor.4 These organisms are saprophytes and invade only dead plants, causing postharvest product loss in drying rooms and product storage. In addition to product loss, all mold can pose significant health risks. Individuals with upper respiratory problems, such as asthmatics and those who are immunocompromised, should never be exposed to mold-contaminated product.

Drying rooms

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Images 8 (top) and 9. UV-C used in a bud-drying room

Air drying generally is conducted in bud drying rooms where temperature and humidity are tightly controlled. The freshly harvested cannabis buds are placed in racks and suspended from the ceiling of the room (Image 7). Fans positioned on the ceilings and/or walls of the room perform the air dying of the buds.

Fans, in addition to drying the cannabis buds, in some cases, gently rotate the cylindrical racks. The solution in these areas requires installing UV-C lamps on the drying room ceilings and walls (Images 8 and 9).

The exact layout and number of UV-C devices is determined by the size and configuration of the room in addition to drying time and predetermined disinfection rates.

UVC-LED
Image 10. UV-C LED design for HVAC. Images courtesy of Fresh-Aire UV.

The UV-C devices will inactivate mold and bacteria that reside on the surfaces within the room, bud racks and buds. The UV-C devices also can inactivate spores that may be transported and recirculated around the room by the drying fans. Additionally, the HVAC system controlling the room’s temperature and relative humidity should be treated with UV-C as previously described in the second suggested step of the growing room protection (Image 10).

Finished product storage

Since finished product can remain in storage for months at a time, it is critical for the storage room environment to remain pathogen-free. As in both the growing and drying rooms the HVAC system can play a significant role in greatly reducing the exposure to pathogens. Proper design and installation of UV-C in HVAC systems can ensure the air used to control temperature and humidity can be disinfected with every pass through the room environment.

Conclusions

In summary, UV LED devices (Image 10) are a potential multifaceted solution for cannabis growers. Products can be designed to address pathogenic microorganisms at multiple critical points within the growing, harvesting and product storage cycles. These same products can assist the cannabis industry in taking significant steps in trying to achieve sustainable agricultural practices and bringing the industry closer to realizing chemical-free processes. A benefit to UV LED suppliers could mean exponentially higher sales volume, but, more importantly, this intimate and systemic understanding of the customer’s processes turns a supplier into a valued solution provider.

Contact: Timothy Leach, timothyjleach1@gmail.com

REFERENCES

  1. Senge, Peter. The Fifth Discipline: The Art and Practice of the Learning Organization. ISBN Publishing 1990.
  2. McPartland, J.M., Clarke, R.C., Watson, D.P. Hemp Disease and Pests – Biological Control. Chapter 1. CABI Publishing, 2000.
  3. Cook, R.J., Qualset, C.O. Appropriate Oversight for Plants with Inherited Traits for Resistance to Pests. Institute of Food Technologies. 1996
  4. McPartland, J.M., Clarke, R.C., Watson, D.P. Hemp Disease and Pests – Biological Control. Chapter 8. CABI Publishing, 2000.
  5. Daughtrey, M.L., Benson, D.M. 2005. Principals of Plant Health Management for Ornamental Plants, Annual Review Plant Phytopathology 82:243.
  6. Suthaparan, A. et al. Suppression of Powdery Mildew (Podasphaera pannosa) in Greenhouse Roses by Brief Exposure to Supplemental UV-B. Plant Diseases, November 2012
  7. Suthaparan, A. et al. Determination of UV action Spectra Affecting the Infection Process of Oidium neolycopersici, the Cause of Tomato Powdery Mildew. Journal of Photochemistry & Photobiology, B: Biology. January 2016.
  8. Heijde, R.Ulm., UV-B Photoreceptor-mediated Signaling in Plants. Trends Plant Science. 17 (2012) 230-237.
  9. Hugenholtz, P., Fuerst, J. Heterotrophic Bacteria in an Air-Handling System. Applied and Environmental Microbiology, Dec. 1992, P. 3914-3920
  10. Leach, T., Scheir, R. Ultra Violet Germicidal Irradiation (UVGI) in Hospital HVAC Decreases Ventilator Associated Pneumonia. ASHRAE, NY-14-C023
  11. Levetin, E., Shaughnessy, R., Rogers, C.A., Scheir, R. Effectiveness of Germicidal UV Radiation for Reducing Fungal Contamination within Air-Handling Units. Applied and Environmental Microbiology, Aug. 2001, p. 3712-3715
  12. Ryan, R.M., Wilding, G.E., Wynn, R.J., Holm, B.A., Leach, C.L. Effect of enhanced ultraviolet germicidal irradiation the heating ventilation and air conditioning system on ventilator-associated pneumonia in a neonatal intensive care unit. Journal of Perinatology. (2011), 1-8
  13. Leach, T., Taylor, G., Restoring Acceptable HVAC Performance with Ultraviolet Germicidal Irradiation (UVGI) Coil Treatment. ASHRAE, Winter Conference. January 2017.
  14. ASHRAE. 2013. ASHRAE Handbook—HVAC Design Manual for Hospitals and Clinics, Atlanta: ASHRAE.
  15. ASHRAE. 2015. ASHRAE Handbook—HVAC Applications, Atlanta: ASHRAE.ASHRAE. 2016. ASHRAE Handbook—HVAC Systems and Equipment, Atlanta: ASHRAE.
  16. ANSI/ASHRAE-SPC-185.2-2014. Method of Testing Ulratviolet Lamps for use in HVAC&R or Air Ducts to Inactivate Microorganisms on Irradiated Surfaces.
  17. www.apic.org/professionals