An introduction to augmented biocontrol in indoor cannabis
by Robert “Bob” Starnes
Despite the controlled environment of indoor cannabis cultivation, experienced growers know that pests always find a way in. They can enter because of a number of reasons, many of which are related to lapses in proper sanitation and quarantine procedures such as bringing in infected plants from a nursery, not properly sanitizing clothing before entering each grow room, or using contaminated tools.
In a perfectly balanced outdoor natural ecosystem, the pest populations would stay under control thanks to their natural enemies, also known as “beneficials”, which are predators and parasitoids naturally present in the environment. Unfortunately, because indoor cannabis production systems are disconnected from their surrounding ecosystems, populations of natural enemies capable of keeping a pest under the economic threshold level (ETL) are rarely present. This is the reason why most growers spray pesticides throughout the vegetative and early flower stages. The good news is, there is a pest management technique that allows cannabis growers to mimic what’s happening in nature and control pests even more efficiently than potentially harmful synthetic pesticides.
AUGMENTATIVE BIOLOGICAL CONTROL IN ACTION
Growers who implement biocontrol as part of their Integrated Pest Management (IPM) plan can re-release natural enemies on a regular basis instead of using pesticides. This technique of introducing mass-reared beneficial insects or mites into a grow is referred to as augmentative biocontrol. In addition to the fact that in many cases it is one of the only available pest management options for cannabis growers allowed by regulators, biocontrol presents many advantages compared to the use of chemical applications even where sprays won’t result in failed tests. For example, some cannabis pests develop pesticide resistance (sprays are not as effective on new generations of the pest), forcing growers to look for alternative pest control strategies. The efficacy of the biological control agents, on the other hand, doesn’t lower over time. Additionally, some sprays are known to negatively affect the plant by reducing photosynthesis. Another argument (among many) in favor of augmentative biocontrol is that sprayed chemicals often cannot reach some pests such as spider mites which tend to stay sheltered on the bottom side of leaves, while natural enemies have no problem finding them there.
WHAT IS THE DIFFERENCE BETWEEN INOCULATIVE AND INUNDATIVE AUGMENTATION?
The primary principle of augmentative biocontrol is to use periodic releases to ensure that there is a large enough population of natural enemies to prevent or control major pest outbreaks.
Augmentation can be further segmented into inoculation and inundation, depending on the frequency of release.
Inoculative augmentation is when a release of beneficials is made on the plants once during the season and the control is ensured for the rest of the season by their offspring.
Inundative releases are planned when the pests are only controlled by the released beneficials themselves since future generations generally don’t survive to control future pest outbreaks. In that case, more frequent releases are necessary over the season.
Many cannabis pests, and this is especially true for indoor facilities, are successfully controlled using augmentative biocontrol: mites (two-spotted spider mites, broad mites, russet mites), thrips, aphids, and whiteflies by using either predators or parasitoids depending on the target. One common example is controlling the populations of two-spotted spider mites (Tetranychus urticae) in cannabis by releasing a beneficial predator mite, Phytoseiulus persimilis. This mite, which is probably the most effective specialist predator of two-spotted spider mites, is released on the crop every two weeks. Another famous augmentative biological control use case is the release of the parasitoid wasp “Aphidius colemani” to control aphid populations.
If you are wondering about how to start using these control agents, rest assured you will not have to rear the insects yourself. Several companies specialize in the mass production of beneficials, from home breeders to multinational corporations. Your PCA or a local entomologist should be able to recommend one (my company, Shale Peak Horticulture offers recommendation to its clients and would be happy to answer your questions if you don’t have a PCA).
WHEN AND HOW TO RELEASE BENEFICIALS IN THE GROW?
To ensure the success of your beneficial release, it is important to take a preventative rather than a curative approach. Trying to control a major pest outbreak can be difficult, impacting the overall budget and threatening the entire production. While a small spider mite outbreak might cost $1,000 to get rid of in a 3,200 square foot facility, a serious outbreak could cost $4,000-5,000 and up! IPM advisors can help growers to plan a release schedule before starting the new crop cycle, making sure the right beneficials are released at the appropriate rate during each stage of the crop’s development.
Beneficial insects and mites are usually mixed with a carrier material such as vermiculite or buckwheat and come in small bottles, sachets, buckets or tubes. Depending on what stage of flower they are in, shaker bottles like the one containing Neoseiulus californicus, Phytoseiulus persimilis, Amblyseius swirskii or Aphidius colemani can be sprinkled on the plant leaves. Growers should release them as soon as possible after they receive them in temperature controlled containers from the insectary. The standard application method is to gently rotate each shaker bottle while holding it parallel to the floor (on its side) before and periodically during applications to ensure an even amount of beneficials come out with each shake (If the bottle is left vertical for too long, the bugs could crawl towards the light and bunch up at the top, thus making the second half of the bottle less effective). The mites are released by shaking the bottles over the crop and leaving the empty ones open at the end of each row so that the last remaining bugs can crawl out. Crops past the second week of flowering need a hanging distribution box to keep the vermiculite out of the flowers. Past week three, growers should make sure to never sprinkle on the flower because too much vermiculite will get trapped on the flower resin and contaminate the finished product.
On the left: sachets containing predatory mites.
On the right: Bottle containing predatory mites shaked on top of the plants.
Depending on the predator, buckets can be sprinkled on top of the blocks, pots or beds of soil - as long as they don’t get blasted by direct water they will be fine at the base of the plant.
If pest populations are anticipated to grow but are not yet sufficient to sustain a larger beneficial population, sachets containing all life stages of the natural enemy provide a safe place for them to grow while feeding on grain mites. Sachets also maintain a slightly higher humidity to stimulate growth of the bugs. Growers can place sachets in the garden at any stage of flower to create a standing army that will be ready whenever the pest arrives because the older mites slowly leave the sachets over a four week period. If there are truly no pest pressures in the garden, some additional products can be sprinkled to provide a food source to keep the mites happy, eliminating their need to leave in search of food.
Do you have any experience with augmentative biological control? Share your story with us and fellow growers in the comments!