Despite its name, Hop latent viroid (HLVd) has become a material threat to both cannabis and hop growers worldwide. Although most HLVd-infected plants remain asymptomatic, research on hops has demonstrated a decrease in both the α-bitter acid and terpene content of hop cones, which affects their economic value. In Cannabis, HLVd-associated “dudding” or “duds” disease of cannabis was first reported in 2019 in California.

By 2023, disease has become widespread in cannabis-growing facilities across North America, and is estimated to have infected up to 90% of the commercial cannabis crop. A number of severe  yield loss associated with duds disease have been recorded highlighting the potential economic impact. Although, little effort has been made to understand the impact of this latent virus on consumer health despite it’s believed pervasiveness across California commercial crop. Like in hops, only a few cultivars of cannabis show HLVd-associated symptoms, implying that both symptom expression and disease severity are cultivar genotype dependent. Additionally, expression of HLVd-associated symptoms may be time dependent (with some phenotypes of grape exhibiting the curled leaves associated with “dudding” 5-7 years after infection). Before exploring the potential impact to consumer, a brief review of the RNA viroid itself. 

What is Hop Latent Viroid?

 Hop Latent Viroid (HpLVd) is known to infect hop plants (Humulus lupulus). The term “latent” in its name refers to the fact that infection with this viroid often doesn’t lead to visible symptoms in the host plant under normal conditions. In some cases, it may remain asymptomatic in the plant, causing no apparent harm.

Upon infecting cannabis plants, potential effects could include:

1. Symptomless Infection: As is the case with hop plants, cannabis plants infected with HpLVd might not show any noticeable symptoms. However, the viroid could still be present in the plant tissue and could be spread to other plants.
2. Reduced Yield: HpLVd could potentially reduce the yield of cannabis plants. In hop plants, HpLVd infection can lead to a smaller yield, and similar effects might be observed in cannabis plants.
3. Altered Plant Physiology: Though it’s speculative, HpLVd infection might alter the physiology of cannabis plants. For instance, it could potentially affect the production of cannabinoids, the compounds responsible for many of the medicinal properties of cannabis.
4. Disease Synergy: If cannabis plants are infected with other pathogens, HpLVd infection could potentially exacerbate the effects of these diseases.

As viroids don’t encode for proteins, their pathogenicity is believed to be due to their interactions with the host plant’s metabolic processes, including RNA silencing mechanisms. Some viroids can also induce changes in the expression of host genes, which can lead to disease symptoms. However, the specific mechanisms through which HpLVd interacts with hop plants at a molecular level remain an area of ongoing research.

How Does HPLvD affect Marijuana efficacy & safety?

True story… last year around this time (June / July) I developed Cannabis Hyperemesis after ingesting (via smoking flower) ascend wellness marijuana  from New Jersey. The weed was tightly packed, decent nug structure aesthetically, and made vomit continuously for nearly 60 hours. THC did not explain it, I’d been consuming excessively for some time, but this tested weed was different. It made me terrifyingly sick. Well, it took an additional year, but it appears we finally identified the driver. In fact, in “Fool’s gold: diseased marijuana and cannabis hyperemesis syndrome” Oscar Armando Dorantes brings up the obvious point that originally eluded much of the academic community. That no reported cases of hyperemesis have involved testing for pathogens on the underlying weed.

As a latent virus, HPLvD only reveals itself in certain phenotypes or when combined with another pathogen to achieve disease synergy. That said, research indicates that the disease impacts terpenes, trichomes, and ultimately THC. Additionally, there are likely less easily measured impacts of smoking an infected plant. In fact,  we believe it this RNA viroid is the likely culprit behind the degradation on marijuana quality in both New York’s significant gray / black market and nascent licensed model. For example, in February we tested two high end pounds that were quite literally dirt despite high marks on smell, overall nug structure, and coloration. Feedback included a lack of effectiveness, nausea, itchy throat, and headache. The flower came from San Bernadino Valley from high end, reputable boutique growers. It turns out the HPLvD viroid emerged in 2019 in the same vicinity. So, although we cannot verifiably state that both hyperemesis and other unpleasant experiences hitting the weed market are direct result of  HPLvD we certainly have our suspicions.

Are there tests for Hop Latent Virus? Or is this weed Armageddon?

 Yes, there are tests. Except growers are not required to perform these pathogen tests and dispensaries don’t report them. Pathogen tests may be performed by providing tissue samples of mother plants (which assures against an infected batch on the assumption cloning occurs under fully sterile conditions), and on site tests are offered to test at the root level. One could argue that commercially licensed THC content and overall Terpene profile could provide some indication, but this information was published on the container on the marijuana that got me sick (despite being a well-educated consumer who pays attention). Additionally, extract based products such as vape & edibles likely are not impacted in the same way.

 Despite availability of testing, and presumed safety in extract based products we still fear that HpLV has the potential to further contribute to diaspora in the weed market by providing consumers an unreliable experience without explanation. Additionally, “media” covering the viroid appears to be paid content for both testing and growers claiming to produce viroid resistant “purple weed”. We fully believe that an informed consumer is the cornerstone to a healthy market, but ‘dud’ resistant strains leave tremendous amount of unknowns in terms of consumer safety. A latent virus often does not reveal itself (much like COVID amongst certain individuals). Additionally, adopting distribution models such as vertical “micro business” licenses will benefit the industry by providing enhanced diversification by relying on fresh genetics and direct sourcing for the industry to thrive. Let’s hope New York adopts that route.