Earlier this summer, the team at Dark Heart Nursery announced the findings of a formal survey of cannabis growers across California: After some 200,000 tissue tests, 90% of California facilities researched were testing positive for hop latent viroid (HpLVD).
All told, the presence of that pathogen—to that degree—could account for a $4-billion loss in cannabis crops, according to the Dark Heart team.
The tests ran across more than 100 licensed cannabis facilities, from August 2018 to July 2021. This endeavor began during the research phase that saw Dark Heart connect HpLVd to a suite of worrying symptoms known as “dudders” or “dudding” at the time. This included stunted plants, low trichome production, weak stems and so on.
“Very early on, we knew there was this problem in the industry where plants wouldn't produce: low yields, low trichomes. We took the time to do the science, to do some RNA sequencing and figure out what was the actual cause of that. Hop latent viroid was only in the infected [plants], not in the healthy ones.” But simply identifying the pathogen was not enough. Once it was found, the Dark Heart team removed the pathogen, isolated it in a pure culture and then infected an otherwise healthy plant with it. Quickly, they noticed the familiar symptoms.
From there, the question became: How widespread is this issue? Cannabis forums were already lighting up with anecdotal stories of dudding plants.
Warren took the scientific approach used to connect HpLVd with the disease and began to tour licensed cannabis facilities in California, going to the places where reports of 20% crop loss were coming through loud and clear. The work focused on nursery stock that would eventually become a business’s mother plants and involved PCR (polymerase chain reaction)testing in a clean environment to detect the presence of the virus. (PCR testing will sound familiar to anyone who’s been exposed to the COVID-19 virus in the past year or so.)
Once the present of HpLVd is confirmed (or even before then), what’s a grower to do?
“You’ve got to get team buy-in,” Warren says. “There are growers who have their own mother blocks, and they run their own genetics. No. 1 for everything for this viroid is sanitation. It’s spread by people, usually pruners, cutting an infected plant and then taking [scissors] to a healthy plant, infecting it.” (Warren said that Dark Heart has forthcoming research that will get into the infection rate with more specificity, as well as differences in infection rates among varying grow environments.)
From there, ongoing testing of mother plants is critical. Three to four tests per nursery plant is key, Warren says, due to the aforementioned latent nature of the virus.
“What these tests have showed us is, if you get in and do the test, after a month and a half, which is what this three- or four-test timeframe [requires], you can go from 40% infected in your grow to between 0% and 1%,” Warren says, pointing out that infected plants are thrown away immediately. “That yield, the money we’re talking about there, is realizable very quickly.”
As for the $4-billion figure, the Dark Heart team is tabulating a possible 33% loss on the $11.9 billion in total cannabis sales thus far in 2021 (according to New Frontier Data).
Crop yield is the backbone of the cannabis supply chain, of course. What grower doesn’t want to increase yield? Identifying this gap between projections and actual yield is the place where this HpLVd research can come in handy. It remains a significant issue for the industry.
Dark Heart’s testing research continues—and Warren points out that this is not a problem confined to California. He says the work serves the dual purpose of ringing an alarm bell for nursery owners and growers in other parts of the world.