Features Management Research
Research update on cannabis and rice root aphid management

Greenhouse Canada recently connected with researchers from Niagara College’s Horticultural & Environmental Sciences Innovation Centre (HESIC) to get an update on some of the research being carried out on managing aphids species that are wreaking havoc in some greenhouses. The following is a Q and A with HESIC’s Scott Golem and Sebastien Jacob.

Can you elaborate on the challenges that cannabis aphids and rice root aphids pose to cannabis crops?
Cannabis aphids (Phorodon cannabis) and rice root aphids pose significant challenges to cannabis crops, impacting yields, plant health, and ultimately, the bottom line for Canadian cannabis growers. The impact of these pests is multifaceted, affecting various growth parameters such as vigour, photosynthetic rate, and plant height, and they become particularly problematic when winged aphids get caught in the final product. The presence of honeydew and sooty mold, which are byproducts of aphid infestations, have been observed and continues to be a concern.

The impact of cannabis aphids on THC content, in one study conducted by Jason Lemay (2022), showed that there was no effect on THC concentration in one cannabis cultivar, indicating that the primary concern with cannabis aphids might not be on the cannabinoid levels but more on the growth and physical quality of the plants. However, this observation might not extend to all cultivars or to other aspects of plant development and health. On the other hand, a thesis from Eze Pojmann-Ezeonyilo (2022) indicated that Phorodon cannabis reduced hemp bud dry mass and THC and CBD content, highlighting a direct impact on yield and cannabinoid profiles in hemp, which suggests that the impact may vary between hemp and cannabis, or among different cultivars.

The industry has learned much about managing Phorodon cannabis since the legalization of cannabis, adopting strategies like starting with clean stock, quarantining new plants, and employing cultural and physical approaches, including heat treatment during greenhouse sanitation processes. Improved management practices, including the efficient use of biopesticides and the development of a more favourable environment for these products, have made the pest more manageable but it remains a common threat. The introduction of Hop-Latent Viroid (HLVd) free material from tissue culture has also contributed to better pest management.

The challenge with rice root aphids has similarly decreased, attributed to preventive and curative approaches, including the use of repetitive biopesticide drenches. There seems to be a buildup of beneficial fungi in the root zones, aiding in the overall reduction of these aphids in the industry. The endophytic capacity of these fungal biopesticides might be impacting the overall reduction of rice root aphids, though the challenge persists in both
cannabis and hemp in the U.S. and Canada, becoming a growing issue in nursery crops as well (pers. Comm. Jacob, 2024).

Some of your research has focused on managing these pests as traditional methods have proven ineffective. What have you and your team discovered about best practices for managing them?
Our research into managing cannabis aphids and rice root aphids, particularly in the context of Canadian cannabis production, has illuminated several key insights and best practices for dealing with these pests. Given the limited pest management options against these pests, for rice root aphids, we and our partners mainly focus on finding key novel products, aiming at achieving higher efficacy and faster results with fewer applications. Most importantly, we wanted to assess the phytotoxicity risk of various products, rates, and number of applications.

The findings from various studies highlight a nuanced approach to pest management that balances efficacy against potential phytotoxic effects. While repeated drench applications of biopesticides can be effective, their concentration and frequency of application need careful consideration to avoid negative impacts on plant growth and yields. New products tested for managing rice root aphids demonstrated more than 90 per cent efficacy in both propagation and vegetative plants. However, these products also exhibited phytotoxicity on the root zone, highlighting a common challenge in pest management: finding solutions that are both effective against pests and safe for the plants. 

Niagara College researcher Sebastien Jacob at a facility conducting research, in partnership with Koppert Canada, on the effect of humidity and wind on cannabis aphids. Photo: Koppert.

Aphidius matricariae emerging and Chrysopa on cannabis leaf. Photo: Koppert.

Rice root aphids in the soil and on clones. Photo S. Jacob

An article published in Greenhouse Canada last year, indicated precise environmental controls and careful cultivar selection are key to enhancing biological controls of pests like the cannabis aphid, can you elaborate?
The relationship between environmental controls, cultivar selection, and the efficacy of biological controls in managing pests like the cannabis aphid is complex and multifaceted. Our research, conducted in collaboration with Koppert Canada Ltd., assessed the impacts of various combinations of wind speed and relative humidity, on the efficacy of two beneficials, either alone or in combination (Aphidius matricariae and Chrysopa carnea) at reducing cannabis populations on two different cultivars (cultivars confidential as per the source).

Wind and humidity had a significant impact on the effectiveness of these biological control agents. Specifically, we discovered that the efficacy of beneficial insects was dramatically increased by maintaining lower wind speeds and keeping humidity levels consistent and at higher values. This insight underscores the importance of precise environmental control in greenhouse settings to maximize crop yields, aid in disease management and achieve the full potential of biological pest and disease control methods. For example, if the wind speed exceeds 2 m/s at the plant canopy and RH is lower than 45 to 50 per cent, this severely impacts the efficacy of these parasitoids. Similarly, management of Botrytis bud rot can’t be achieved with just low humidity and more air flow; many other strategies must be implemented, including reduced plant density and spraying with biofungicides like Rootshield HC at proper timing (Mahmoud et al., 2023).

These conditions not only favour the optimal performance of the beneficial insects but also support a more favourable Vapor Pressure Deficit (VPD) for cannabis growth. This insight is critical as it underscores the importance of precise environmental control in greenhouse settings to maximize the potential of biological pest control methods. Recent publications on Botrytis bud rot disease management (Simon Fraser University, with collaborators) provide many other insightful strategies (eg. flower shape, plant density, sprays of Rootshield HC, etc.) but finding the right balance in steady humidity levels at critical times for both pests and diseases is important.

Our research also explored the role of cultivar selection in pest management, particularly focusing on the differential susceptibility of cannabis cultivars to aphid infestation and disease. Although specific details about the cultivars remain confidential, our findings revealed differences in pest and disease dynamics between indica and sativa commercial cultivars. For example, from an initial inoculation of three aphids per plant, one cultivar experienced an 8-12-fold increase in aphid population within four weeks, while the other exhibited a higher susceptibility to powdery mildew. These results highlight the complex interactions between cultivars, pest populations, and disease incidence. Selecting cultivars that are less attractive to pests can reduce the burden of pest management and improve efficacy of biological control agents.

Can you share details on some of the targeted root/soil treatments in controlling rice root aphids your team looked into?
Our team has explored various targeted root and soil treatments to control rice root aphids in cannabis cultivation, considering the balance between efficacy against the pest and safety for the plants. To briefly summarize our overall findings, there are three main things to look at.

Efficacy vs. Phytotoxicity: Finding a balance between controlling the pest and avoiding harm to the plant is crucial. Our trials suggest that while certain biopesticides and treatments can be effective, they may also pose risks to plant health if not applied judiciously.

Environmental conditions: The effectiveness of soil treatments can be influenced by the growing conditions, including soil type, moisture levels, and other environmental factors. Optimizing these conditions can enhance the efficacy of treatments and support plant health.

Integrated Pest Management (IPM): Root and soil treatments should be part of a broader IPM strategy that includes biological controls, environmental management, and selection of cultivars more unfavourable to pest levels. This holistic approach can help manage pest populations more effectively and sustainably.

How might the findings of this study impact the broader cannabis industry in terms of yield improvement and reduction of crop losses?

The findings from our studies on pest management in cannabis cultivation, particularly focusing on aphids and root aphids, have significant implications for the broader cannabis industry, especially in terms of yield improvement and reduction of crop losses. Here’s how our research could impact the industry:

Filling Knowledge Gaps: Our research contributes to filling the substantial knowledge gaps in the cannabis industry regarding pest management. By systematically investigating novel solutions for pests like the cannabis aphid and rice root aphid, as well as testing various control measures, we provide data-driven insights that can inform more effective pest management strategies. While our studies have added valuable information, there remains much to explore and understand about pest dynamics in cannabis cultivation.

Encouraging Collaboration and Open Sharing: Sharing findings and collaborating openly with IPM companies, researchers, and students is critical for the advancement of the cannabis industry. By fostering a culture of openness about challenges and successes, the industry can collectively advance more robust and sustainable pest management strategies.

Exploring New Research Avenues: Our interest in further studies, such as investigating the effects of Herbivore Plant Induced Volatiles (HIPVs) on beneficial insects and pests, and conducting efficacy trials on other predators like Anystis, mirids, and nabids, in collaboration with other research groups already investigating these, points to the potential for broadening the scope of pest management research in cannabis.

Impact on Yield Improvement and Crop Loss Reduction: By enhancing our understanding of pest management in cannabis and identifying effective strategies for controlling pests like aphids, our research can help reduce crop losses and improve yields. Effective pest management not only protects the plants from damage but also ensures the quality of the cannabis product, which is crucial for both medical and recreational markets.

Scott Golem (Research Lead) and Sebastian Jacob (Faculty Research Lead) are team members at Niagara College’s Horticultural & Environmental Sciences Innovation Centre (HESIC). All research mentioned in this article carried out at Niagara College was completed by HESIC. To learn more, visit ncinnovation.ca.