Cultivating cannabis on a commercial scale can mean many things: higher yields, more revenue, and greater return on investment to name a few. However, one thing for which many large-scale growers aren’t prepared is the frequency and severity of cannabis pathogens.

In many cases, growers don’t realize they’ve had an outbreak until it’s too late. To protect their plants, people and bottom line, cultivators need a comprehensive disease management program that includes intervention and prevention strategies.

Why Do Pathogens Matter to Cultivators?

Because even the best designed facilities have them. The question is, have you invested in robust mechanical solutions that can limit their impact on your financial performance, and do you know how to use those tools to create action plans to reduce risks and solve problems when they occur? 

Certificates of analysis (COAs) tell us the percentage of cannabinoids and terpenes, but they also tell if products are safe to sell and consume. If they are not, they need to go through remediation (which often destroys the price per pound) or destroyed all together. In other words, pathogens not only impact your plant yield, morphology, and phenotypic expression, but the profitability of your entire business. 

When Do Pathogens Form?

A better question might be, when do they not form? If you cultivate cannabis long enough, you will cultivate pathogens. The study “Pathogens and Molds Affecting Production and Quality of Cannabis sativa L.” reminds us why. Every time you touch, cut, transplant, or trim a plant it becomes more vulnerable to infection. Not only are there many ways in which an infection can spread, but there are also many sources from which pathogens can develop, including decaying plant material, substrate (such as coco fiber), water, mechanical equipment, hand tools, parking lots, the feet of insect pests, and people.

Knowing the Enemy: Common Cannabis Pathogens

So how do you design a facility that minimizes the risk of pathogens and allows you to stay on the path of success? You need to know your enemy, how they grow, and where they grow.

During their study, Punja et al. sought to identify and understand fungi affecting cannabis roots, foliage, and flowers grown in indoor, greenhouse, and field environments. And a handful of key culprits were discovered. 

Pythium will take your moms . . .

. . . and infect all plants moving forward. Pythium is usually spread through water, making it a particularly high risk when substrates become anaerobic. The symptoms of infection include browned roots, discolored crowns, and even plant death. 

Fusarium will take your roots and stems . . . 

A root-infecting pathogen, Fusarium species typically live in your substrates and, like Pythium, can cause root rot and crown rot.

Botrytis will take your fruits during curing . . .

Spread through the air and through vegetative propagation, Botrytis is a necrotrophic pathogen that causes brown spots on inflorescences and can lead to major losses during curing and storage. 

Penicillium will take your fruits during trimming . . .

Penicillium species often cause bud rot or decay during trimming and defoliation process, which opens up “wounds” through which the pathogen can enter the plant.   

Powdery mildew will take your sanity . . .

Characterized by its white powdery appearance, powdery mildew appears is prevalent in cannabis foliage and, in fact, most cannabis grow operations as a whole. 

And HPLV and other endophytic fungi will take your whole facility, and you might not even know it until it’s too late. Pathogens are not always visible, so even the healthiest looking plants can still be infected.

Managing Your Pathogen Risk

Once you know which pathogens you’re up against, it’s time to implement mitigation strategies. While further research still needs to be done on strain-specific disease management, here are nine things to consider for commercial cannabis cultivation when managing pathogen risks.

​​Ensure proper drainage. Your cultivation trays should have an appropriate slope (around 1 inch) so that water doesn’t pool and choke your substrate. The water needs to drain fully without any drain blockages.

Measure volumetric water content in your media. From there, adjust fertigation appropriately. This helps to maintain an air to water balance, prevent conditions where pathogens thrive and give you accurate drybacks for crop steering.

Eliminate stagnant air. Collisions of air, improper velocity, lack of air balancing, and poor supply/return configurations all lead to “dead” spaces in the room where microclimates persist and pathogens thrive. Investing in appropriate airflow solutions — especially in multi-tier in-rack airflow — helps facilitate full air exchanges in the space, homogenize leaf temperatures and produce consistent growth. Often, a simple anemometer can help assess the effectiveness of airflow in your cultivation environment, help correct issues and justify investments in supplemental airflow solutions.

Invest in air filtration. Every cultivator knows the value of airflow, but clean air is key. If you are bringing in outside air, you need to pursue the right level of filtration to make sure you eliminate any threats. Even if you don’t bring in outside air, the ductwork or HVAC system that delivers conditioned air to the space can be the culprit. Filtration solutions like photocatalytic oxidation (PCO) or other technology help you ensure the air delivered to the plants is free of pathogens. Additionally, while pathogen counts might rise in a facility over time, these solutions ensure they will never break the economic impact threshold.

Clean rooms between runs. This one seems obvious, but its importance can’t be overstated. Clean the cultivation space, the floor, the walls, the floor drains and even the tools you are using to clean. Take it a step further if you want to get ahead of pathogens. Clean the fan blades and guards, the coils on your dehumidifier, hand tools, the drain pans, hallways and connecting spaces just as diligently as the cultivation room.

Test your grow media. Send a sample of your cultivation substrate to a lab for testing to receive valuable insights regarding the presence and population of pathogens. You should also be testing the root zone temperature — one of  the cardinal parameters of plant growth and a critical indicator of whether you’ve created an environment that lets pathogens, rather than roots, thrive.

Test mother stock regularly. Remember cannabis is an annual crop, and if you have mother plants that are a few years old they might be harboring dangerous secrets. We can fight powdery mildew and pathogens we see on mother plants, but it is important to know what potential pathogens you might be breeding with every cutting. It all starts with your moms, so send a sample off for testing on a regular basis so you can develop the appropriate action plan to future-proof your production.

Invest in environmental control. Adherence to setpoint is important for plant vitality, controlling leaf temperature and consistent production, and it is a major factor that influences pathogen growth and spread. One example is avoiding massive delta in vapor pressure deficit (VPD) from lights on to lights off. If these spikes occur every time the lights turn off, you will inevitably find yourself cultivating plants in conditions perfect for developing powdery mildew or Botrytis. Managing your environmental itinerary from day to night and week to week can prevent pathogens from ever gaining the upper hand.

Invest in your people. Your people can be the source of many pathogens, but they don’t have to be. With detailed standard operating procedures (SOPs), employees can save crops, identify issues and make your facility scalable. They should know, for example, how to cut with clean scissors at the right time in the right way and how to trim appropriately with the right personal protective equipment (PPE). Plants don’t grow themselves, people do. Empower you people with the tools and training so they are not the pathogen vector but instead the pathogen solution.

​​Pathogens are all around us. They are in the bathroom, parking lot, drains, ductwork and the hands of every employee. Understanding this and putting together fundamental SOPs and corrective and preventive action (CAPA) plans will make sure your facility avoids outbreaks that destroy your crop, your profitability and your brand.