Routine scouting for disease symptoms is a critical part of any plant pathogen testing program.
You know you can’t reliably spot a viroid spreading in your grow room.
You’ve determined whether on-site plant pathogen testing equipment is right for your facility.
Now you want to know: how do you start a testing program? The right testing strategy can save you money and reduce plant damage.
Your cannabis plant pathogen testing strategy should cover two main components: how to test and what to test.
How to test cannabis plants for pathogens
First off, your team should be trained on how to use your testing equipment and test kits. When you purchase testing equipment, make sure your team is trained in the machine and test kits. If your testing machine provider does not offer free initial training, consider using a different vendor.
Use a systematic testing approach
Be systematic with your sampling and keep good records.
- Pre-label your sample extraction bags with plant identifiers and sample location information.
- Collect samples and put them in the appropriate sample extraction bag.
- Track each container from sample extraction to diluent tube to the final reaction tube. Enter that ID information into the testing machine. The machine will generate a report of test results with the ID information provided.
Use sterile sampling techniques
Team members working in your grow room should understand your crop and how to safely take samples.
- Use sterile sampling equipment. Sap on equipment and sap on your gloves can be a vector of transmission for viroids.
- Train your team on proper sterilization techniques for tools, equipment and surfaces.
- Avoid excessive damage to well-established roots.
Determine whether to combine samples
For the highest accuracy, test each sample separately. If cost savings is your priority, you can combine 3-5 samples together.
However, when you combine, there is a risk of diluting the viroid. If one of your samples is positive and the rest are negative, you might dilute the viroid to an undetectable amount. Additionally, samples are combined, if a sample tests positive additional testing may be needed to locate the location of the infected tissue.
Every test result depends on the quality of the sample you collect.
Which cannabis plants to test — and how often
Figure 1. Prioritize testing on new clones, mother plants and vegetative plants while continuing random sampling throughout the grow cycle.
How often you test and how many samples you take depends on your budget. It also depends on the prevalence of viroids in your area. For example, viroids like Hop latent viroid (HLVd) are currently highly prevalent in North America. Testing can help you eliminate viroids before they spread in your grow room, but if your testing regularly finds no viroids and your crops appear healthy, you may consider reducing the number of tests because your risk appears low.
We recommend prioritizing testing on early-stage growth plants. This is because testing early-growth plants will prevent you from pouring money into lighting, nutrients, and caring for plants that may ultimately need to be destroyed.
Following is a breakdown of our recommended testing schedule by growth stage.
Plants that show symptoms of infection
Be vigilant about testing any plants that don’t look like they should. Are they too short? Test. Do they have curly leaves? Test. Plants that show symptoms of infection should be tested no matter what stage of growth they are in.
If plants test positive, consider destroying the infected plant. Also consider testing neighboring plants or plants that share recirculating water with the viroid-positive plant.
New genetics, strains, or clones from another provider.
Many growers receive cuttings with new genetic material from other providers. Always buy from reliable sources and test as soon as roots are available.
- If the cuttings are unrooted, put the clone in a soil block with water and soil. In early-stage growth, viroids like HLVd are typically first detectable in root samples and may not show up in leaf samples. As soon as enough root material is available, take a root sample and test it.
- If you buy pre-rooted cuttings, test the roots right away.
We suggest testing all new plant material that enters your facility.
Young mother plants that are actively growing
For young mother plants that are actively growing, consider prioritizing root samples over samples from other parts of the plant. Early-stage infection can be difficult to detect in above-ground tissue, but the roots tend to harbor higher concentrations of Hop latent viroid. Any plants that are younger than six weeks old should prioritize root samples.
For rapidly growing mother plants, consider a two-week schedule for testing.
Established mother plants
The tests you perform on mother plants will provide the most value. Mother plants provide cuttings for plants down the line, so it’s essential that they are healthy and viroid-free. We recommend testing every mother plant when taking cuttings, or at least every two to four weeks.
Figure 2. Four recommended sample locations from a mature mother plant. If the mother plant is more than 2 months old, take special care with root samples or consider omitting root samples.
For an established mother plant, a good protocol is to take around four samples per plant per testing event.
- One or two samples of petiole or basal leaf tissue from old growth
- One to two samples of petiole or basal leaf tissue from new growth
- One to two root samples
On mother plants two months and older, take special care not to damage the root system by digging too deeply or disturbing well-established roots. Consider eliminating root sampling from older or more valuable mother plants.
Consider a monthly testing schedule for an established mother plant.
Vegetative stage
We recommend less testing at this stage. You could test on the same schedule as you test your mother plants (every two to four weeks) but take fewer random samples.
Similar to the mother plant testing, we recommend taking samples from various parts of the plant, including the petiole, new leaf growth, old leaf growth, and the roots.
By prioritizing testing at earlier stages of growth and implementing good hygiene practices, you should have reduced the likelihood that plants in later stages of growth will be impacted by HLVd.
Consider a two-week testing schedule for plants in the vegetative stage.
Flowering stage
Typically, growers do not perform scheduled testing when cannabis plants are in flower. However, if a plant or group of plants is showing symptoms, those should be tested.
If plants test positive, your team should work to discover how pathogens entered the grow room by asking questions like:
- Are your plant hygiene practices in place?
- Were plants missed in earlier stages of testing?
- Could you have an infected mother plant?
The goal is to find out how HLVd entered your grow room and work to prevent the spread and eliminate future problems.
What if a sample tests positive
If a sample tests positive for HLVd or other viroids, consider destroying the impacted plant to prevent spread. There are some biological and chemical treatment options for fungal pathogens such as Fusarium oxysporum. But if you are sampling early and often, ideally you will catch pathogens early in the growth cycle, when destroying impacted plants may be the most cost-effective option.
If you want to protect a mother plant of a rare or valuable genetic strain, you may attempt to find uninfected areas of the plant to take cuttings from. Plants grown from tissue culture or cuttings from infected plants should undergo a rigorous testing program.
However, in most cases, if you have a plant or clone that tests positive, we recommend destroying the plant.
“Nothing needs to leave the building. Everything can be plucked right off the plant and tested almost immediately,” says Nick Denney, Director of Cultivation, Holistic Industries
Contact us
We’re proud to introduce the new Amplifire® Pro machine (coming soon!) for plant pathogen testing with PCR-level accuracy. The machine is modular and can be configured to test up to 32 samples and 4 pathogens in less than 30 minutes, all in a machine that fits in a suitcase.
Amplifire® Pro is the testing machine. Buy AmplifyRP® test kits for a wide range of pathogens.
We’d love to talk with you about how we help you grow a healthy and profitable cannabis crop by empowering you to find and remove plants impacted by Hop latent viroid, Fusarium oxysporum, or other cannabis plant pathogens.
