HpLVd: the viroid that silently threatens cannabis crops

The HpLVd (Hop latent viroid, or latent hop viroid) is now considered the most serious health threat to the North American cannabis industry - and is beginning to worry European growers. Discreet, asymptomatic for weeks at a time, and capable of halving the production of THC and terpenes, It has earned some industry experts the nickname «the Covid of cannabis».

What is a viroid?

Before you can understand HpLVd, you need to understand what a viroid because many people confuse it with a virus, whereas these are two radically different entities.

A viroid is a plant pathogen composed solely of one of the following single-stranded circular RNA molecule, no protein, no envelope, no capsid. It is the smallest known infectious agent: HpLVd is only 256 nucleotides. Where a virus has at least one surface protein to penetrate cells, the viroid has nothing, and is entirely dependent on the host plant's cellular metabolism to replicate.

Paradoxically, this extreme simplicity makes it very difficult to eliminate: no target protein for treatment, no structure to destabilize. Only the destruction of the RNA itself works.

Origins and discoveries about cannabis

HpLVd has been known since 1988 as a pathogen of hops (Humulus lupulus), a plant in the same botanical family as cannabis (Cannabaceae). On hops, its effects remain relatively limited - moderate reduction in bitter acids and cone terpenes.

His switch to cannabis was first documented in 2019 in California, confirmed simultaneously by two independent teams via high-throughput sequencing. In retrospect, growers had begun discussing unexplained symptoms on their plants online as early as 2014, called «duds» or «dudding disease», without being able to identify the cause.

Since then, progress has been lightning-fast. A Dark Heart Nursery Research study of 200,000 tissue tests estimated that 90% production facilities in California were contaminated, with losses estimated at 4 billion dollars a year for the American industry. In Canada, a Simon Fraser University study found that 40% of cannabis flowers sold in dispensaries tested positive for HpLVd.

Symptoms: dud disease«

The most dangerous feature of HpLVd is its frequently asymptomatic, an infected plant can appear perfectly healthy throughout its vegetative phase, while actively spreading the viroid to its surroundings.

When symptoms appear, it's usually in bloom, stage when the concentration of detectable viroid in tissues is at its highest:

• Stunted smaller plants, reduced internodes, shorter stems
• Underdeveloped trichomes smaller trichome heads, «deflated» appearance under the microscope
• Smaller, less dense flowers poorly formed calyxes, poor flowering
• Deformed leaves chlorosis, slight curling, yellowing near flowering sites
• Reduced odor and aroma significant loss of volatile terpenes
• Brittle, brittle stems in cases of severe infection

The economic impact is direct: studies document up to 50% discount THC and terpene content of infected flowers, and a reduction in fresh weight of inflorescences from 12 to 42%.

Transmission modes

HpLVd is remarkably contagious and spreads by several simultaneous routes:

Mechanical transmission This is the main vector in cultivation. Any non-disinfected tool (scissors, scalpels, stakes) that has been in contact with an infected plant can transmit the viroid to the next one. Simple contact between leaves may suffice if the epidermis is damaged.

Via the clones If the mother plant is infected (even asymptomatically), 100% of the cuttings taken will be infected. This is the main vector for large-scale propagation in professional facilities.

Via seeds HpLVd was detected in the pollen and seeds of infected plants, with seedling infection rates ranging from 58 to 80% depending on the study.

Via nutrient solution in hydroponics The viroid was detected in the recirculated nutrient solutions of the multiplication tables and in the nozzles of the systems. aeroponics, This makes it a particularly formidable vector for soil-less cultivation.

Survival in the environment HpLVd is remarkably stable: it survives 5 days on gloves at room temperature, and up to 4 weeks on dried leaves. It withstands exposure to 70°C and UV-C, two conventional disinfection methods that are insufficient on their own.

What works to eliminate it

Bleach 5-10% (NaOCl 0.825%): the only chemical disinfection that has been shown to effectively degrade viral RNA. Use to decontaminate tools, surfaces and equipment.

Hypochlorous acid at 1000 ppm Less corrosive alternative to bleach, also effective in degrading HpLVd.

Meristem tissue culture apical meristem cultivation can be used to produce viroid-free clones from infected plants, but this is a time-consuming, technical and costly process, reserved for genetically valuable cultivars.

Systematic elimination of positive plants The most well-documented approach is regular RT-PCR testing and elimination of positive plants. Dr. Zamir Punja's team (Simon Fraser University) reduced the infection rate of a plant from 35% to 7% in 7 months by applying this protocol.

What doesn't work Temperatures up to 70°C, UV-C alone, and most common disinfectants (Virkon, Zerotol) do not reliably eliminate HpLVd according to available data.

Prevention: best practices

In the absence of curative treatment, prevention is the only effective strategy:

Testing mother plants This is the most important control point in the entire production chain.

Systematic disinfection all cutting tools with diluted bleach between each plant, without exception.

Quarantine any new plant material introduced into the growing area, even if purchased from a trusted source.

Never share tools between separate growing areas without complete disinfection.

Isolating nutrient solutions at hydroponics, It's important not to recirculate a common solution between multiplication tables and culture.

Setting sticky traps and control aphids (Phorodon cannabis, Rhopalosiphum rufiabdominale), a 2025 study confirmed that certain aphid species can acquire and transmit HpLVd from an infected plant to a healthy one.

Situation in Europe and France

HpLVd has been officially present in Europe, notably in hop fields in Germany, the Czech Republic and Slovenia, for decades. Its presence in European cannabis cultivation is less well documented than in North America, due to a more restrictive legal framework that limits large-scale studies.

However, the growth of legal medical cannabis in Europe (including France, with its current experiment) and the exchange of plant material make the introduction and spread of HpLVd inevitable in the long term. Legal producers and experienced growers would do well to integrate testing and disinfection protocols into their practices now, before the problem reaches North American proportions.