When Should You Test for HLVd? Early Clone Screening Is Best

Hop latent viroid (HLVd) is one of the most damaging and widespread pathogens currently threatening cannabis cultivation. What makes HLVd particularly difficult is its ability to spread silently. Early infections are often asymptomatic, allowing the viroid to move undetected through entire facilities. By the time symptoms become visible, the economic damage is already done, with reduced yields and significant drops in THC and CBC content. 

Preventing the introduction and spread of HLVd requires strict adherence to sanitation protocols, quarantine and testing of new genetics, and routine screening of mother plants to detect and remove infections before they spread. Yet despite the importance of testing, best practices around what tissues to test, and when, are not always well defined.

Emerging research consistently points to root tissue as the most reliable sample type for HLVd detection. But that raises important questions: When during the plant’s growth cycle should you test? What stage gives you the best chance of catching infections early, before the pathogen has time to spread?

TUMI Genomics + Statehouse Holdings: A Data-Driven Collaboration

To help answer these questions, TUMI Genomics partnered with Statehouse Holdings to conduct a rigorous, time-course study of HLVd infection dynamics. In this experiment, 180 freshly cut clones across 12 cannabis strains were artificially inoculated with hop latent viroid. These plants were then tested at regular intervals using our triplex, TaqMan qRT-PCR, with results normalized to a cannabis housekeeping gene to allow viroid levels to be compared across different growth stages.

The goal: understand how viroid levels change over time and pinpoint the most effective window for early detection.

Key Findings: HLVd is Highest in Clones and Flower

• At 3 weeks post-cloning, freshly rooted clones consistently showed high levels of HLVd. This makes early clone testing an ideal opportunity to identify infected plants before they enter production.

• Surprisingly, viroid levels dropped significantly during the vegetative phase. By 6 to 9 weeks post-cloning, many infected plants had undetectable levels of HLVd

• Once plants entered the flowering phase, viroid levels spiked rapidly, reaching their highest concentrations by harvest.
  

Shows normalized HLVd levels in inoculated plants through various growth stages. Note the sharp decline in viroid load at the end of vegetative growth.  Error bars = Standard Error of the Mean.

What This Means for Cultivators

The data clearly show that testing early, particularly at the freshly rooted clone stage, offers the best chance of detecting HLVd. This is especially critical if clones were inadvertently sourced from a positive mother or could have been exposed during propagation.

While it may be tempting to wait until plants are further along before testing, the vegetative dip in viroid titer means you’re more likely to miss infections at that stage. Testing freshly rooted clones allows for simple integration of root testing during transplanting and ensures valuable resources are not wasted growing infected plants.

Best Practices for HLVd Detection

• Test freshly rooted clones (2–3 weeks post-planting), using root tissue, which provides the most reliable viroid signal.

• Quarantine and test all incoming genetics; never assume a plant is clean without confirmation.

• Routinely test mother plants, and always test immediately before cutting clones. This helps to identify any plants that may have been exposed after propagation.

Work with TUMI for Reliable HLVd Testing & Prevention

Understanding when to test is just as important as knowing what to test. With robust, time-course data in hand, cultivators can now make more informed decisions about the best way to integrate viroid testing into their production. 

If you’re a cannabis cultivator concerned about HLVd, contact TUMI Genomics—our proprietary TumiGlow Diagnostic Device is specifically built for HLVd and offers unparalleled protection for your yield.