Dealing with Molds, Mildews, and other Nasties in Cannabis Production

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

o   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!

Posted by: Talia Plaskett

Making the Most of your IPM Programs

    You found out that you have an insect infestation in your crop, and identified the causal agent. What comes next in deciding how to handle it?

1.       You need to consider the life stage of the target pest. Biological controls are skilled at targeting pests, but this can be restricted to certain stages of the life cycle. Those that are specialized at targeting larvae are not going to be able to knock back a population that is mostly comprised of eggs or adults. While interruption of the life cycle is important for combatting pest outbreaks, you won't necessarily limit the feeding damage that is to come as a result of the current population. 
2.       The life stage of the pest is not the only thing to consider. If you are relying on insects to control your pest population, you need to consider the life stage of the biological you are wanting to use. Releasing eggs compared to releasing larvae can result in different levels of control, establishment and active period in the crop. 
3.       Life stage, life stage, life stage! Where is the crop at in terms of its production cycle? Some biologicals are best applied in the early stages compared to the later ones. For example, releasing an agent that is going to lay eggs that hatch and congregate around the flowers is going to render your product unusable. 
4.       What are the growing conditions in the production space? Similar to plants, diseases and insect pests, biological interventions are going to have an optimum set of conditions to maximize performance. This is especially important when you are growing at lower/higher temperatures and abnormal humidity levels. Some biologicals are going to operate better at lower temperatures ( ex. 10C) compared to others, and you don't want to waste your time repeat testing an agent that is not going to thrive in that particular setting.

      Now that we have decided which biological control agents we want to use, there are a few other things to keep in mind. 

1.       How healthy are the predators that I've ordered? It is important to check the viability of your biological control agents upon receiving them from the insectary. There can be issues with rearing, storage/shipping etc, which can result in sub-optimal pest management. By implementing these health checks before releasing into the crop, you can ensure that you are getting the best quality product and setting your IPM program up for success
2.       It is ideal that you are always releasing fresh biological agents. By storing them for long periods of thime, you are running the risk that they will parasitize each other in their storage container. You could also be reducing the activity of the agents, and will need to spend more money in the long run. By purchasing the amount that you will release each time around, you are one step closer to maximizing the effectiveness of your agent. 
3.       Are the agents I've ordered compatible with each other? While it is likely that you will get some overlap of introduced biological control agents targeting each other, you want to make sure that is not the norm
4.       Are the agents I've ordered compatible with the spray activities happening in the grow room? Oil sprays that are used to suppress insects and disease are not always selective when it comes to drowning out pests.

   Maximizing success and implementing a successful IPM strategy can be a long process, but  taking these things into consideration should help get things started. Preventative pest management strategies are crucial in creating and maintaining a healthy and productive grow space, and there is no time like the present to dive in and re-evaluate your current strategy! 

      Posted by: Talia Plaskett

SUMMARY of BugBites! Session 5: Fungus Gnats and Shore Flies

Review Part 2: Shore Fly Management

While shore files (Ephydridae) are primarily seen as a nuisance in protected production spaces, they can also degrade the quality of your plants. Adults are known to leave 'fly vomit' behind as they make their way through the production space. These small black specks can be found on plant parts and growing surfaces, and are no aesthetic addition to your pristine green canopies. 

The following information is a summary of session 5 of the BugBites Series: Fungus Gnats and Shorefly Suppression with Beneficial Organisms. To watch the full session, click here! 

Pest Description: 

Adult shore flies, although similar in size to a fungus gnat, are comparable to regular house flies in appearance. These insects can be identified by the 5 white spots on their wings. 

Larvae are semi-aquatic, which can be identified by their Y-shaped breathing tubes. The larvae are semi-aquatic in nature, and can range from cream-coloured to brown.  

Monitoring and Scouting: 

Traditional yellow sticky cards are effective for monitoring and catching adult shore flies. These insects are much stronger fliers compared to fungus gnats, so placement of the yellow sticky cards right at the soil line is less critical. 

Biological Control Options: 

The best method for managing shore fly populations is to manage algae build-up around the facility. The larvae, which are semi-aquatic, rely on algae as their food source. By removing a key part of their reproductive cycle, pest population sizes will be limited. The best way to manage algae is to repair any leaky points along the irrigation system, and carefully sloped surfaces to keep water from pooling. 

Next is insect management. By conducting regular scouting checks of the crop, and maintaining populations of biological control agents, you can limit the degree of pest infestation.

Dalotia coriaria; Rove beetle

• Predator to both shoreflies and fungus gnats
• Both adults and larvae are predatory
• Orange larvae are noticeable in the soil
• Adults readily move around via flight
• Ready establish in greenhouses
• Works well in hydroponic systems

Figure 2. A photo of a rove beetle in the adult (left) and larval (right) stages. stuck to a yellow sticky card.  Image taken from the BugBites! Session 5 presentation

The use of rearing boxes allows for a slow-release approach, and will help maintain beetle populations through the season. Rearing boxes can be as basic as media (ex. peat, vermiculite) set inside a Tupperware container, and supplemented with food (ex dog or fish food, artemia). It is crucial to keep this moist, but not wet. These can be placed under benches.

Steinernema feltiae; entemopathogenic nematode

• Target fungus gnats, shoreflies, thrips pupae and many others
• Forage in the top inch or two of the soil
• Water into your growing media lightly- if they get too far in, they will not be able to combat pest populations
• Not highly mobile
• 50-78F are ideal conditions
• Well suited for greenhouse environments
• Susceptible to being washed away in rockwool
• When growing in rockwool, apply after the last irrigation of the day to give them a chance to establish

Steinernema carpocapsae, entemopathogenic nematode

• Target shore flies, and thrips pupae
• Good at finding mobile pests
• No problem working in/establishing on rockwool
• Lives on soil surface (use very little water when applying to prevent from washing them too deep into the growing media)
• Ideal temp is 57-84
• well suited for greenhouse environments

* Both nematodes listed here can be applied together, since they focus on different parts of the soil.

The key for management here is prevention. By adding nematodes and rove beetles into your production routine, and managing algae growth around the facility, shore fly populations should be significantly reduced. 

Posted by: Talia Plaskett

SUMMARY of BugBites! Session 5: Fungus Gnats and Shore Flies

Review pt 1:Fungus Gnats

Although fungus gnats (Sciaridae) are primarily seen as a nuisance in indoor production spaces, they are responsible for a lot more than that! As a result of their favourite food source (plant roots), these pests are capable of acquiring and spreading fungal disease amongst the crop.

The following information is a summary of session 5 of the BugBites Series: Fungus Gnats and Shorefly Suppression with Beneficial Organisms. To watch the full session, click here! 

Pest Description: 

Adult fungus gnats are mosquito-like insects with long legs, and a characteristic y-shaped wing vein. Adults can be found hanging around or near the soil, mostly under plant canopy. The fungus gnat larvae are white with a shiny black head. Larvae spend most of their time underground and will feed on the roots. 

Figure 1. A photo of an adult fungus gnat stuck to a yellow sticky card. Below, is an image of the fungus gnat larvae. If you look closely, you can see the characteristic black head at the end of the larva. Image taken from the BugBites! Session 5 presentation. 

Monitoring and Scouting: 

Adults are not strong fliers, meaning that sticky cards will only be effective when placed close to the soil line. If placed correctly, traditional sticky cards are a great tool to monitor population sizes.

As an attractant, some growers will use half a potato, or a potato slice, placed in a pot to draw larvae up from the soil. As the larvae are accustomed to feeding on roots, the use of a tuber is a big draw.

For the adults there are various traps available. These traps typically involve the use of an attractant (ex. UV bulb) and a way to capture the insects (sticky cards, soapy water solution etc.). This is useful for general scouting purposes as well as mass trapping.

Biological Control Options: 

As with any biological control program, prevention is the first line of defense in controlling population sizes. By conducting regular scouting checks of the crop, and maintaining populations of biological control agents, you can limit the degree of pest infestation.

Dalotia coriaria; Rove beetle

•  Predator to both shoreflies and fungus gnats
•  Both adults and larvae are predators
• Orange larvae will be noticeable in your soil
• Adults readily move around via flight

• Establish readily in greenhouses and work well in hydroponic systems
  
  

Figure 2. A photo of a rove beetle in the adult (left) and larval (right) stages. stuck to a yellow sticky card.  Image taken from the BugBites! Session 5 presentation

The use of rearing boxes allows for a slow-release approach and will help maintain beetle populations through the season. Rearing boxes can be as basic as media (ex. peat, vermiculite) set inside a Tupperware container, and supplemented with food (ex dog or fish food, artemia). It is crucial to keep this moist, but not wet. These can be placed under benches.

Bacillus thuringeniensis israeleinsis 

•  Functions as a stomach toxin for fungus gnats
•  Best applied via soil drench or chemigation. Irrigation is not ideal as the soil needs to get very wet to allow for good establishment of the biopesticide

Stratiolaelaps scimitus; predatory mite

• Target fungus gnat larvae
•  Well suited for greenhouse environments: optimum development temperature of 25^oC (77^oF)
• Ideal range is 15-30^oC (59-86^oF)
• Live in the top half inch of the soil: best applied to the substrate surface after transplant
• Want to avoid burying too deep in the growing media
• Does not establish well in rockwool
• Persistent control agents, and can provide season-long protection

                                               

Figure 3. An image of an adult predatory mite. Image taken from the BugBites! Session 5 presentation

S. scimitus can be mixed with Dalotia, but it is not recommended to introduce them before adding into the crop. They will feed on each other, so make sure they are spread evenly throughout the canopy when distributed.

Steinernema feltiae; entemopathogenic nematode

• Target fungus gnats, shoreflies, thrips pupae and many others
• Forage in the top inch or two of the soil
• Water into your growing media lightly- if they get too far in, they will not work
• Not highly mobile
• Well suited for greenhouse environments with an ideal temperature range of 10-25^oC (50-78^oF)

• Susceptible to being washed away in rockwool
• When growing in rockwool, apply after the last irrigation of the day to give them a chance to establish

By ensuring thorough protection against all life stages of the fungus gnat, you should be able to keep populations at bay! Prevention is everything, so be sure to apply biologicals preventatively and as needed.

Posted by: Talia Plaskett

Proper Release of Biological Control Agents

Biological control is a key part of managing pest populations in cannabis production. While it is extremely important to conduct regular scouting and know the appropriate control methods to tackle your target pest populations it does not guarantee a successful biological control program.

It is important to check the quality of the product you are receiving from the insectary: 

• Are the biologicals alive? 
• Are they of good quality and form? 
• Were they stored and shipped properly? 

There are countless stories of producers who received product that was sub-optimal, and their IPM programs suffered as a result. By checking the quality of every shipment you receive from your insectary, you are one step closer to a successful biological control program. This does not guarantee that the product will be high quality, but you will be able to salvage the situation. Contact the insectary, voice your concerns, and be prepared to put in another order of biologicals. The alternative? Vast amounts of time and money spent on a program that is not working effectively, and a crop infested with pests.

Now that you know that your biologicals are in good form, it is time to release them! Knowing where in the crop to place them, how to properly store them, and the best way to handle the insect housing, are all important to maximize pest control. OMAFRA and the team at Vineland Research and Innovation Centre got together to talk about the proper release of biological controls. Click the following link to watch the video and see how your practices hold up!

Posted by: Talia Plaskett