Even though cannabis grown indoors is protected from Mother Nature, it remains vulnerable to pests and pathogens. Growing dense stands of plants in a humid, enclosed environment can lead to infestations and infections.
But growers can reduce the risk of outbreaks by implementing Integrated Pest Management (IPM)—an effective, environmentally sensitive way to manage pests and pathogens that seeks to prevent infestations and infections from occurring in the first place and uses multiple control methods to address issues if they arise.[1]
Determine tolerable levels
IPM is a four-tiered approach. The first step involves setting a so-called “action threshold”—a point at which pest and pathogen populations justify action to reverse or contain the outbreak. “Sighting a single pest does not always mean control is needed,” states the IPM Principles.[2] Pest or pathogen populations must justify intervention by posing an “economic threat” to the grow. Think of action thresholds at quantitative triggers; if the action threshold for a specific pest or pathogen is crossed, the grower should take concrete steps to deal with the problem.
Monitor and identify
The second step in IPM is to monitor for potential problems and identify risks. Doing so ensures that pests or pathogens are caught early—before they can harm crops and cause business losses (i.e., pose an economic threat)—and that the proper treatments are applied.
Scouting is a primary practice of monitoring and can range from simple to sophisticated, with growers visually checking plants or employing technology to detect and report issues, especially in larger grow operations. However, manual checks should always be done in addition to any technology used to verify what the system is reporting, especially with incoming plants.
Sticky cards and pheromone traps are effective for detecting pests, identifying them and recording their populations. The action thresholds set in the first step of IPM help determine when action is needed to stop pests from reaching damaging levels. Although over 270 species of insects and mites have been recorded on cannabis, few are considered economic pests or pathogens.[3] Unnecessary treatments are costly and may increase the risk of resistance to pesticides.
Monitoring is also crucial after outbreaks occur to ensure treatments are working. For example, growers can use indicator plants to monitor the effectiveness of a treatment. These are plants that growers can designate and scout routinely by closely examining how pests or pathogens are responding to a treatment throughout their life cycle.[4]
Prevent
The third step in IPM is to prevent outbreaks from happening, if possible.
Technically, monitoring is already part of prevention. New plants should be inspected and quarantined before their introduction into closed environments to ensure pests and pathogens are kept out of the grow room.
But if threats do enter, growers can take other preventive measures to keep them from getting a firm foothold, primarily by creating an environment that is not conducive for them.
For example, one reason powdery mildew and root rot are prevalent in grow rooms is due to environmental inconsistencies when the lights are off, as plants continue to transpire for 45–90 minutes after the photoperiod ends. As the temperature drops in the dark, affecting humidity, an environment susceptible to pests and pathogens is fostered.[5]
However, growers can maintain a more consistent growing environment with a high-performance heating, cooling, air conditioning and dehumidification (HVACD) system, which allows for precise control of temperature, humidity and airflow. These factors impact microbial sporulation, pest-mating cycles and overall IPM efficacy. Refer to our “Equipment for Indoor Growing” blog post for more information on the necessary equipment to create an ideal climate for cannabis.
Control
Despite a grower’s best efforts, pests and pathogens may still find their way into the grow room and start to escalate. If this happens, the final step in IPM is to control them.
Pests and pathogens can be controlled, in ascending order, by cultural, physical, biological or, as a last resort, chemical means.
Figure 1. The IPM triangle. Cultural control is the foundation of IPM, followed by physical and biological methods. Chemical controls should be used only as a last resort. Image source: See footnote 4.
Physical
Physical control methods include pest traps, barriers, and removing diseased plants from the grow room or pests from plants.
Biological
Chemical
Chemical control methods include pesticides, bactericides and fungicides—all of which should be used as a last resort, particularly synthetic ones, as they may pose a threat to humans or the environment. Whenever possible, opt for organic or natural options—for instance, azadirachtin, which is derived from neem tree seeds, is effective against pests like fungus gnat larvae.[10]
Figure 2. An alternative or complement to IPM, integrated disease management (IDM) strategies (left panel, in brown) are developed according to the crop development stage (top panel). The hexagons (in green) illustrate the specific diseases being targeted. HLVd = hop latent viroid; PM = powdery mildew; Botrytis cinerea = bud rot.[11]
Putting IPM into practice
Let’s summarize some practical measures every cannabis grower can take to implement IPM and prevent pest and disease outbreaks:
- Focus on plant health. Healthy plants can better fight off pests and pathogens. Choose mother plants that are infection-free.
- Keep your facility clean and organized. Seal potential points of entry for pests and pathogens and establish protocols to prevent them from hitching a ride on workers or equipment, such as using sticky mats before entering the grow room.
- Inspect and quarantine all new plant material. Keep new plants in a separate area for several days to ensure problems do not develop.
- Maintain preventative environmental conditions. Appropriate humidity levels are crucial to minimizing pathogen growth.
Refer to the following tables for tips on dealing with specific pests and pathogens.
Table 1. Common pests that infect cannabis and their respective management options.
Pathogens
Management options
Aphids
If a plant is infested, move the container outside and spray it to reduce the population. Remove heavily infected leaves and buds. Reduce ambient relative humidity and improve air circulation. Use insecticidal soap or organic controls to minimize activity.
Thrips
Apply biological controls at rooting or organic chemical controls.
Spider mites
Control heat and blow air constantly over the plants to create cooler temperatures, making it harder for them to reproduce. Remove diseased cuttings.
Broad mites
Use organic chemical control to curb the infestation.
Barnacles
Use a small one-hand pressure sprayer to spray off the bugs. Use an organic chemical control like neem oil.
Leaf miners
Environmental control indoors and in greenhouses prevents bugs from laying eggs in plants. Remove affected leaves if possible; if not, crush the larva by squeezing where the trail is visible. Use an organic chemical control.
Caterpillars
Sprays and biological controls are effective.
Common diseases
Pathogens
Management options
Damping off
Botrytis cinerea
Reduce ambient relative humidity and improve air circulation.
Fusarium oxysporum
Apply biological controls at rooting.
Fusarium proliferatum
Removed diseased cuttings.
Fusarium solani
Removed diseased cuttings.
Root and crown rot
Fusarium oxysporum
Test (mother) plants to ensure they are pathogen free.
Fusarium proliferatum
Apply biological controls during the vegetative phase.
Fusarium solani
Avoid injury to the roots and overwatering.
Pythium myriotylum
Avoid excessive watering.
Pythium dissotocum
Avoid root injury.
Pythium aphanidermatum
Apply biological controls at rooting and during the vegetative phase.
Stem canker
Fusarium oxysporum
Test (mother) plants to ensure they are pathogen free.
Fusarium solani
Avoid root injury or overwatering.
Stem rot
Fusarium & Pythium
Test (mother) plants to ensure they are pathogen free and avoid root injury.
Powdery mildew
Golovinomyces spp.
Vegetative cuttings should be disease free. Irradiate leaves for 3–4 seconds with UV-C light daily. Apply weekly treatments of potassium bicarbonate. Grow strains that are tolerant to infection. Vaporize sulfur at night. Remove and destroy diseased leaves.
Bud rots
Botrytis cinerea
Reduce ambient humidity and moisture.
Fusarium spp.
Avoid strains with large, dense flowers that retain moisture. Prune out diseased buds.
Molds (post-harvest)
Botrytis cinerea
Maintain dry grow rooms at optimal humidity and temperature.
Penicillium species
Avoid damaging buds during harvesting and trimming. Irradiate dried buds with gamma or electro-beam radiation.
Dudding
Hop latent viroid
Test stock plants to confirm they are pathogen free. Remove and destroy infected plants.
Leaf spots and blight
Botrytis cinerea
Reduce ambient humidity and moisture.
Wilting and leaf spots
Xanthomonas
Use resistant cultivars and pathogen-free mother plants.
Creating and implementing an IPM strategy not only reduces the likelihood and frequency of outbreaks, but also allows growers to take appropriate, effective control if they arise. Selecting the best control method is essential for effective, sustainable pest-and-pathogen management. Start by accurately identifying the pest or pathogen, and then assess the extent of the infestation to determine the required scale of intervention.
Prioritize non-chemical control methods: cultural (e.g., crop rotation, sanitation), physical (e.g., barriers, traps) and biological controls (e.g., natural predators). If chemical control methods are needed, opt for organic controls like neem oil or diatomaceous earth; use synthetic pesticides, bactericides or fungicides only as a last resort while strictly adhering to the label instructions.
Remember that the best implementation of IPM combines multiple methods. Consider each control method’s cost, efficacy, safety, environmental impact, resource usage and sustainability to ensure a balanced yet effective pest control strategy.
Emerald Harvest Team
[1] United States Environmental Protection Agency. n.d. “Integrated Pest Management (IPM) Principles.” Last updated September 20, 2023. https://www.epa.gov/safepestcontrol/integrated-pest-management-ipm-principles.
[2] Ibid.
[3] Lemay, Jason, Youbin Zheng, and Cynthia Scott-Dupree. 2022. “Factors Influencing the Efficacy of Biological Control Agents Used to Manage Insect Pests in Indoor Cannabis (Cannabis sativa) Cultivation.” Frontiers in Agronomy 4. https://doi.org/10.3389.fagro.2022.795989.
[4] University of Massachusetts Amherst. n.d. “IPM Scouting and Decision Making.” Updated 2016. https://ag.umass.edu/greenhouse-floriculture/fact-sheets/ipm-scouting-decision-making.
[5] Schimelpfenig, Gretchen, Jesse Porter, and Craig Burg. 2021. “Integrated Pest Management for Cannabis Cultivation Monitoring, Identifying, Preventing, and Controlling Pests with HVAC Solutions.” Cannabis Science and Technology, July/August 2021 4(6): 18-25. https://www.cannabissciencetech.com/view/integrated-pest-management-for-cannabis-cultivation-monitoring-identifying-preventing-and-controlling-pests-with-hvac-solutions
[6] University of Wisconsin–Madison. n.d. “Cultural Control.” Accessed July 23, 2024. https://vegento.russell.wisc.edu/ipm/cultural-control/.
[7] Wolfe, Kathy. 2020. “Trap Cropping.” June 12, 2020. https://s3.wp.wsu.edu/uploads/sites/2073/2020/07/Trap-Cropping.pdf
[8] Colorado State University. n.d. “Cannabis aphid.” Accessed July 23, 2024. https://agsci.colostate.edu/agbio/ipm-pests/cannabis-aphid/.
[9] BioWorks Inc. 2021. “RootShield HC – Biological Fungicide Wettable Powder.” Accessed July 23, 2024. https://bioworksinc.com/wp-content/uploads/products/rootshield-hc-ca/RootShield-HC-English.pdf.
[10] Cranshaw, Whitney. 2017. “Pesticides Allowed for Managing Insects and Mites on Cannabis in Colorado.” Accessed July 23, 2024. https://webdoc.agsci.colostate.edu/hempinsects/PDFs/Allowable%20Insecticides%20for%20Cannabis%20in%20Colorado.pdf.
[11] Buirs, Liam, and Zamir K. Punja. 2024. “Integrated Management of Pathogens and Microbes in Cannabis sativa L. (Cannabis) under Greenhouse Conditions.” Plants 13(6): 786. https://doi.org/10.3390/plants13060786.
[12] Punja, Zamir K. 2021. “Emerging diseases of Cannabis sativa and sustainable management.” Pest Management Science 77(9): 3857-3870. https://doi.org/10.1002/ps.6307.
