Hop Latent Viroid (HLVd) is a dangerous infectious pathogen that poses a significant threat to the global cannabis and hop industry. First discovered in 2018, this viroid has quickly spread beyond North America, prompting cultivation experts to label it the “biggest concern for cannabis and hop growers worldwide.

The viroid is transmitted from plant to plant through a variety of ways, including contaminated tools, human touch, and pests, is most commonly spread through the use of trimming tools used for vegetative propagation and grafting. It moves quickly throughout the plant, from root to the leaves to the flower in just two to three weeks.

Infected plants often struggle to grow normally, leading to shorter stature and underdeveloped trichomes, causing THC and CBD levels to drop significantly.

The viroid is most noticeable during the flowering stage, where it can become even more virulent due to the stress caused by lighting change.

Since its initial detection in 2019 in California, the “duds” disease of cannabis has become the most devastating plant disease for the cannabis industry.

A survey conducted in 2021 by Dark Heart Nursery Research utilized 200,000 tissue tests and concluded that 90% of cannabis-growing facilities in California were contaminated with HLVd. Researchers noted that since HLVd infection could significantly affect the plants’ vigor and yield the viroid could have catastrophic implications on the value and results of cannabis crops.

It is estimated that annual losses to the cannabis industry, directly caused by HLVd could exceed $4 billion.

For operators, an infection can be debilitating.

Cultivators can take preventive measures to curb the spread of the viroid, such as having their plants regularly tested, but there are no guarantees.

Researchers suggest that HLVd is likely present in most commercially licensed cannabis production facilities in the United States and Canada, with an estimated frequency of infected plants ranging from 25%-50% in both countries.

The most effective way to prevent infection is to ensure tools are sterilized between use.

Sterilization of cutting tools and equipment between each plant is critical for limiting spread within a facility, especially since infected plants can appear asymptomatic. However, some sterilization techniques are ineffective against viroids. Sterilization solutions often used and found effective against bacterial or fungal pathogens are ineffective against viroids including HLVd.

A 2015 study recommended several disinfectants, including 2% Virkon S, 10% Clorox regular bleach, and 20% nonfat dry milk, to greenhouse facilities for consideration to prevent general virus and viroid infection on tomato plants.

More recently, TUMI Genomics evaluated results of fifty-three different chemicals and treatments of viroid infections. Among these, five tested treatments showed 100% effectiveness at viroid deactivation. While most of these chemicals were shown to be effective against specific viroids, only household bleach (sodium hypochlorite – NaClO), demonstrated broad effectiveness across numerous studies, different plant species, and multiple viroids.

With HLVd also transmitted by pests, pest management is an integral part of ensuring crop safety.

Should an infection occur, there is no treatment for HLVd, but tissue culture techniques can be utilized to harvest uninfected material from HLVd-infected plants.

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