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Hop Latent Viroid Plagues Cannabis Crops: Dr. Jeremy Warren of Dark Heart Industries Delivers a Solution

Interview with Jeremy Warren, Ph.D., of Dark Heart Industries

By Lance Griffin


Hop latent viroid (HpLVd) looms among the largest threats to cannabis cultivation. Growers know it as dudding. Affected cannabis plants suffer stunting, low yields, poor potency, brittle stems, and reduced vigor. HpLVd causes massive crop losses; according to Dark Heart Industries, it affects more than 30% of legal cannabis and costs U.S. cultivators about $4 billion per year.

Dark Heart Industries would know: they identified HpLVd as the cause of dudding in 2017. Led by Jeremy Warren, Ph.D., Director of Plant Science and Laboratory Director, the company then launched a four-year investigation spanning over 100 cannabis cultivators in California. They developed a clean-up solution that effectively destroys HpLVd.

“We have a cannabis specific, plant pathogen diagnostics lab that growers can send in samples for cannabis diseases including HpLVd,” Dr. Warren explained. “These data were generated specifically from customers who sent in plant material to be tested for HpLVd. So, it’s fairly representative of the most common cannabis grow types.”

The Dark Heart lab employs a probe-based real-time quantitative polymerase chain reaction (RT-qPCR) for diagnosis of the viroid. “This is the most sensitive, high throughput diagnostic test out there and is the same test they use for COVID testing,” Dr. Warren continued. The RT-qPCR machine allows the Dark Heart team to easily interpret results. They set thresholds for positives and negatives and return these simple positive or negative test results to clients.

The demand for such testing has exploded in recent years.

“The most surprising thing is how widespread the viroid is,” Dr. Warren admitted. “We get calls from growers all over the United States, Canada, and Europe. This pathogen is definitely causing major losses worldwide. An initial infection rate can be upwards of 60-70% in some grows.”

Cannabis growers may already know this. In recent years, the mysterious dudding disease proved far more lethal than other known pathogens with known treatments.

Thankfully, Dr. Warren and his team devised a patent-pending cleanup treatment for plants infected with HpLVd.

“After Dark Heart discovered the cause of cannabis dudding disease—hop latent viroid—we performed numerous curing experiments. After about a year of trying methods, we found one that is extremely effective at eliminating the viroid.”

Dr. Warren revealed that “the process combines meristem tissue culture techniques with specific plant pretreatments to create viroid free plants.” The details of this process are protected due to patent-pending status. That said, Bhat & Rao [1] describe meristem tissue culture as “one of the most widely used methods for virus elimination from infected plants and production of virus-free plants.” Generally, pre-treatments may include high temperatures and anti-viral agents. [1] After the clean-up, Dark Heart relies on RT-qPCR to verify disease-free status.

Finding a way to defeat HpLVd was not as simple as it sounds.

“I think one of the biggest challenges is due to the latent nature of the viroid,” Dr. Warren said. “Sometimes the viroid can hang around in the plant at extremely low undetectable levels. So initially when we thought we had a good curing system in place, the viroid would unexpectedly pop back up a few months down the road. It took a lot of trial and error.”

Two plants (same cultivar) growing in the same greenhouse; they are the same age and are actually right next to each other in the greenhouse. The plant on the left is healthy; the plant on the right is infected with HpLVd (also the header image). Note the pronounced difference in trichomes. Although some yellowing is evident in the infected plant, this symptom can be misleading as many pathogens cause yellowing.


HpLVd can spread through contact (e.g., contaminated pruning tools) as well as through infected seeds. Plants are commonly asymptomatic.

Dark Heart Industries produces cannabis flower and pre-rolls with “original varietals that have achieved legendary status.” They also deliver clones and, thus, know the struggle firsthand. “Noticing unproductive plants in our garden and others was one of the triggers for us to undertake the research,” Dr. Warren confessed. “From our study, it turns out that over 90% of nurseries and growers have had to deal with HpLVd.”

HpLVd was discovered in hop plants (note the name). It’s reasonable to believe that Dark Heart’s solution also applies to hops. This may prove a beacon of hope for cannabis and hops cultivators struggling with dudding plants.

Interestingly, OG cultivars seem more susceptible to the disease. Resistant cultivars have not yet been discovered. Dr. Warren sees proper sanitation, clean plants, and ongoing diagnostic testing as a three-pronged strategy to control HpLVd. Single infected plants can be diagnosed and destroyed. Curing an infected crop, however, requires the aforementioned patent-pending method.

“One of the most common misconceptions we hear,” Dr. Warren explained, “is that you can cure plants of the viroid if you do X, Y, or Z. Unfortunately, the only known way to cure plants of the viroid once infected is to do a pretreatment and meristem tissue culture process. X, Y, Z are usually just snake oil-type cures.”

Consumers may wonder if HpLVd poses a health risk. Fortunately, this is not the case— consuming cannabis infected with HpLVd appears harmless.

Today, Dr. Warren continues his cutting-edge research at Dark Heart Industries. “I think one of the biggest challenges in the cannabis industry is the ability of the growers to dramatically scale production to meet consumer demand over the next five years. Specifically, having access to the right genetics enables those growers to achieve that scale.”

He envisions stable hybrid seed as the single most profound innovation facing cannabis. Certified seeds have already transformed the hemp industry.

“We are lucky in that we can look back at 80 years of agricultural innovation in crops like corn, take those lessons learned, and apply them to cannabis,” Dr. Warren concluded. “Since the blueprint for success has already been written, we can follow the work of previous scientists. But the best part is it won’t take us 80 years to get there. We will start seeing these advances in as little as 3-5 years. We think this is a huge opportunity for the cannabis space and is one of the reasons we have focused on these blueprints in developing our own cannabis R&D and breeding program over the last two years.”


Dr. Jeremy Warren, a pioneering cannabis researcher and scientist, leads the plant science division of Dark Heart Industries. He has more than 20 years of experience in the field of plant pathology and was one of the first scientists to discover hop latent viroid in cannabis. He received his B.S. degree in biochemistry from the University of California at Davis in 2000 and his Ph.D. in Plant Pathology from the University of California at Davis in 2015. He pursued postdoctoral research at the University of California at Davis.




  1. Bhat AI, Rao GP. Virus elimination by meristem-tip culture. In: Characterization of Plant Viruses. Springer Protocols Handbooks. Humana; New York, NY.: 2020. https://doi.org/10.1007/978-1-0716-0334-5_47. [Times Cited: 9 (Semantic Scholar)]

About the author

Jeremy Warren, Ph.D., Dark Heart Nursery

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