A very dangerous cannabis pathogen: the Hop Latent Viroid

Since Humankind started farming crops, the fight against the plethora of pests and pathogens has existed. Even when growers transitioned indoors or to a greenhouse, the pressure from pests continued to be present.

Cannabis growers have to deal with a number of pathogens. For them, however, this can be even more stressful because of the strict regulations they have to comply with. “As of now, there are two main issues in commercial cannabis production with minimal information in comparison to all the other IPM issues,” Anoo Solomon, Owner and Director of Operations and Education at CannaProtect IPM Solutions explains. “One is the Cannabis Aphid, but there is also another one that is exceptionally tricky: the Hop Latent Viroid, or HLVd. The availability of peer-reviewed published research on HLVd is very limited, or even non-existent. However, a lot of testing and research is happening currently, and all we need to do is to keep going and figure out how to deal with it.”

Viroids
Viroids are not the same as viruses. “A viroid is basically the smallest infection molecule that can infect the plant,” Anoo points out. “The viroid is only RNA. It has no protein code. It is a single strand – unlike DNA – which means that it is completely dependent on the host metabolism for replication.” Just as with aphids, spotting an HLVd infection is rather complicated. “With the viroid, you don’t get the physical scratching or yellowing,” Anoo continues. “It can be noticeable in the early vegetative phase, as it’s during this stage the most vigorous growth happens. The best and most accurate way to test for this is through PCR testing. Without the testing, you cannot  be sure that a plant is affected by HLVd.”

Look for signs
Yet, as Anoo points out: “The plant tells you if something is wrong. In commercial grow settings, everything is highly regulated and automated, leaving minimal room for error. If you look at the grow space, you see this gorgeous canopy, and then all of a sudden you see this plant that’s small and short with weird-shaped leaves. So, you go by exclusion: look at the irrigation lines, your nutrient feed schedule (is your pH, EC and PPM within range?) then inspect the environmental control. If all of that is on point, you need to look further. In this moment, you have to listen to what the plant is trying to tell you. Every cannabis grower knows that plants speak to us by showing when something is wrong.”

Thus, a cannabis plant affected by the HLVd looks ‘sad and weak’, and it’s fragile. “I have also encountered a situation where two specimens of the same strain were compared,” Anoo continues. “The THC content was actually almost 8% lower in the affected plant. There are theories according to some Growers that cannabinoid content is lower, as well, due to the HLVd. The oil production isn’t of that beautiful, vibrant color, but looks rather lifeless and dull. Another grower said they felt the trichome production was significantly reduced as well.” 

Reduction in yield and quality
Is HLVd a concern for human consumption? “There is no evidence of negative impact on humans,” Anoo points out. “But the real issue is that the crop will experience a reduction in terms of yield and quality.” As usual when it comes to stopping pathogens from spreading, prevention is the best way to go. “Prevention in everything is number one,” Anoo says. “Human vectoring via mechanical transmission is one of the main reasons why the HLVd spreads in cultivation: all equipment and surfaces that come into contact with plants needs to be thoroughly checked and sanitized because that might be the reason why the infection is spreading. If you are working with an infected mother plant, if you do not sanitize your snips and working surfaces, you will spread the infection to your clones. If you are unable to access clean plant material through a reputable meristem tissue culture lab, you can start your prevention plan right in your grow space with your most powerful resource: your team. Train your staff. They need to know what they are looking for. When something looks off, they can take action immediately. At least once a week, it is critical to scout the plants and do a full inspection, or else you are going to have issues. By teaching the staff how to understand what the plants are trying to communicate, you give your team the tools to recognize, treat and prevent further contamination.”

Whatever it takes
When Anoo is brought into a facility, she always goes in with the mindset to save the plant. However, this might prove to be tricky with HLVd. “As the research continues, I hope we get better options. For now, Good Production Practices (GPP) focused on sanitation and hygiene are our best defense,” she says. “As always, implementing strong cultural practices such as starting with clean seeds or cuttings from a reputable source is step number one. If this is not possible, the first recommendation, in any situation with HLVd is to destroy the plant. Any cross contamination via dirty snips can carry the infection through your crop.”

First discovered in hop plantations, the HLVd went from being a non-entity to a significantly problematic entity in the cannabis industry. “Now that we have the recognition and the testing availability, it is crucial to train the staff to understand when the plant is unhealthy, then we’ll be able to have this under control,” Anoo remarks. “Cross-breeding and phenotype hunting might lead to an HLVd -resistant cultivar. Until that time, your GPP comes into play. Start with clean seeds and clones, sanitize the snips and change the gloves and sanitize the area after each use. If you implement these practices in the sanitation protocols, you are greatly reducing the chance of transmission.

“In the meantime, the people that are doing the research love what they are doing and are putting their soul into that. We just have to be patient, stay clean, and wait for them to release their findings, and then we can mitigate the quality and yield loss we are seeing across the industry.”