Hop Latent Viroid: The Hidden Threat To Cannabis Plants

For cannabis growers, infectious diseases result in significant losses of time, money, and labor. As a result, this has been a lively field of study and a hub of activity for plant scientists as they look for solutions to these devastating afflictions. Among these pathogens is the Hop Latent Viroid (HLVd), and it’s a doozy.

HLVd is an infectious disease that causes the stunted growth of the cannabis plant, resulting in a loss of vigor, reductions in potency and yield, and changes in genetic makeup. To add fuel to the fire, the disease can stay dormant and unnoticed for years without showing any symptoms and inadvertently infect other plants in proximity.

The most prevalent manner for HLVd to spread is via contaminated tools and equipment, so it is imperative that growers routinely disinfect their instruments before beginning work on a new plant. HLVd may also be transmitted via cloning when cuttings are obtained from an infected mother.

If left untreated, HLVd could significantly impair the potency and yield of a crop. More than that, other plants may fall victim to the disease leading to a domino effect that isn’t easy to rectify. Once the infection is introduced into a commercial cultivation, it could potentially cause a rapid deterioration of the harvest with an estimated 65% infection rate.

The Origin Story

In 2011, a stone fruit and walnut ranch in Sutter County submitted samples of stray hop plants discovered in a ditch bank for testing to ensure they were free from hop stunt viroid, a subviral pathogen that harms hop plants and produces a severe illness. The samples were found to be negative, but positive for the hop latent viroid (HpLVd).

By 2019, it was almost an epidemic. Bektaş et al. and Warren et al. both reported instances of HpLVd in California in separate studies. Both reports revealed a pathogen that wreaked havoc on commercial cannabis, detected through RT-PCR testing and high-throughput sequencing.

Today, it is a pervasive menace to plants and the efforts of cannabis growers, with little to no means of remediation other than eradication. 

Identifying The Signs

Though some infected plants show no signs of symptoms, the most commonly reported findings of HLVd-infected plants are:

• Reduced potency
• Quality loss 
• Yield loss
• Stunted growth
• Delay in trichome production
• Leaf and branch malformation
• Brittle stems
• Reduced rooting

Dr. Bryce Falk, Professor Emeritus at the University of California, puts it this way:

“Hop latent viroid is perhaps the greatest threat to the legal cannabis industry in the U.S.” 

How Do We Tackle The Problem?

What can you do, as a grower, to avoid the occurrence of this widespread threat to your harvest? How can you practice due diligence as an active participant in the cannabis industry with the responsibility to protect your grow and prevent the spread of HLVd?

It’s all about prevention, and you can take active steps to ensure the safety of your harvest in the following ways:

• To minimize potential cross-contamination, ensure that all scissors and trimming instruments are properly sterile before working on another plant.
• Clean and sterilize your environment regularly.
• Quarantine new clones until they can be tested for HLVd.
• Consistently submit samples for testing.

At MCR Labs, we conduct a Polymerase Chain Reaction (PCR) test to identify HLVd in submitted samples. With this method, we separate a material into its individual plant cells, which lets us extract the RNA and run it through a thermocycler.

In the event that HpLVd is present in the sample, it will replicate in the thermocycler, resulting in the production of hundreds, if not millions, of copies. These copies will be analyzed in order to estimate the amount and severity of the disease.

Do you suspect possible HpLVd contamination in your harvest? Reach out to us and submit your samples for confirmation.