The following is a summary of a presentation put together by Michael Brownbridge, the Biological Program Manager at Bioworks, for the 2022 Canadian Greenhouse Conference. The focus of his talk looks at dealing with disease management using cultural practices and microbial fungicides. For a full copy of the slide deck, check out the 2022 CGC Presentation archives posted.
Cultural practices for disease reduction/prevention:
Cultural practices are day-to-day preventative measures that can be taken that, when properly implemented and adhered to, can collectively reduce the amount of disease introduced/spread through a production space. With a limited number of registered active ingredients in cannabis, it is important to use every tool possible to maintain crop productivity and quality. Some examples of cultural practices to reduce the probability of disease include:
- Strict cleaning protocols (room sterilization, use of clean tools etc)
- Ensure mother plants/ cuttings are disease free by purchasing Verified Clean Stock
- Monitor and maintain suitable growing conditions in each production space
- Consider ‘order of entry’ when moving through the facility in a day – highly sensitive spaces (propagation rooms, for example) should be entered early in the day while workers are ‘clean’ as opposed to the end of a day working with other plants
- When receiving plants from outside of the facility, a quarantine is highly recommended
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While this is valuable from a disease
perspective, it also comes in handy to reduce invasive insect populations as
well. Broad mites, two-spotted spider mite, hemp russet mite, western flower
thrips, and aphids (both rice root and cannabis aphid) are common hitch hikers
on imported materials. All of these are hard to detect and have rapid life cycles.
While they may not be noticeable upon arrival, a few days of quarantine may
reveal populations of tiny insects feasting on the new plant material.
One of the best ways to keep a facility clean is to invest in regular scouting missions and disease screens, especially within the mother room. Diseases caused by Pythium and Fusarium are not always going to show symptoms, which leaves you vulnerable to passing the disease agents into the next round of cuttings. While it is commonly practiced taking cuttings from the top of the plant ‘because the disease isn’t there yet’, recent data from the University of Kentucky shows that although titers may be lower in top parts of the plant, disease is still present. The best way to protect the viability of your future cuttings/crops is to submit plant tissue samples for disease analysis. Taking a subsampling of tissue from different parts of the plant should give an accurate depiction of what may be brewing beneath the surface.
I Have Diseases Developing in the Crop – Now What?
In addition to his work on powdery mildew (as seen in the previous blog post), Zamir Punja of Simon Fraser University conducted some biofungicide efficacy trials against Fusarium oxysporum. Check out his findings below:
The water control is intended to show the level of disease present without a formal introduction of F. oxysporum. The second treatment from the left, referred to as 'Fusarium (+)', shows that the disease isolate used was effective at causing symptoms, and the level of disease that observed throughout the trial when there was no intervention provided.
Now that the two control measures have been addressed, its time to compare product performance. Prestop showed to be the most effective at reducing disease in the inoculated plants. The 'a' on top of the bar here denotes that the level of disease after regular treatment with Prestop is not statistically different than the control treatment. Next up, we see that Rootshield, Asperello and Stargus had significantly less disease compared to the 'Fusarium (+)' treatment. This shows us that these are effective products for reducing symptom development despite the presence of the pathogen. While they may not have reduced disease to the same degree as Prestop, their proper application should lessen the impacts caused by F. oxysporum. Finally we see that Rhapsody and Regalia did not perform very well in this particular trial. Neither product was able to offer any reduction in disease severity compared to the inoculated control.
Dr. Punja conducted similar work for product efficacy against Pythium spp. Looking at the graph above, we can see that 14 days post inoculation with P. myriotylum, plants that were treated with Rootshield and Prestop showed significantly less disease compared to plants that received no treatment. There is no significant difference in the level of disease suppression between these two products against this particular pathogen, based on the findings of this study, which gives growers a bit more flexibility when selecting products for disease suppression.
When in doubt, integrated pest management is the best strategy for reducing the impacts of disease and insect pressure in indoor cannabis production!