Avoiding Pests in the Growroom
A diligent regimen of greenhouse sanitation and a combination of various controls will do wonders to keep insect pests off your cannabis plants. Healthy plants will either prevent the introduction and infestation of pest species or at least better prepared and able to suffer less damage when they (the pest species) do arrive.
Healthy plants that are building up proteins and performing critical botanical functions are less attractive to insect pests. Pests are more difficult to penetrate with their sucking or chewing mouth parts. Sick and stressed plants are more suitable hosts as they are weaker and less able to defend themselves.
The key then to keeping bugs (the bad kind) off your nugs is to make and keep your plants as healthy as possible. This is accomplished through the combination of cultural, mechanical (physical), biological, and chemical control options. It should be noted chemical options should be reserved as a last resort as using them can have a range of unwanted side effects, including the creation of a cycle of dependence on them, making their use more and more necessary and lessening their effects with each subsequent use if they are unchanged or if no variety of formulations is used.
Cultural Pest Controls for Cannabis
Cultural controls may be the easiest method to implement. These involve the way a grower gets things done. Keeping things extra clean in the growroom is the best place to start. This not only refers to the pots, tables or benches, all equipment, floors, walls, and ceiling, it also means keeping the growing area weed free. In between crops, it is always a good idea to use a cleanser approved for use in horticultural settings. These are usually an all-in-one fungicide, virucide, or bactericide formulation that can be mixed and sprayed onto everything to kill all of the pathogens that aren’t visible. These also have the benefit of killing most types of insect pests that may be lingering.
Weeding the pots that plants are in is a must, but so is pulling all the weeds that pop up in floor cracks or along the outside walls of a greenhouse or growing area. These weeds can play host to a wide range of pest species who can then simply wander over to your desirable plants. If used very carefully, herbicides can be used on the floor areas and the areas immediately outside of the growing area. Caution must be taken since any herbicide can cause serious damage or even kill your desirable plants. It is best to do this between crops to avoid the chance of herbicide drift getting onto your plants.
Another way to reduce the chance of getting insects on your plants is to allow some fallow time in your grow area. With no food source present, any pest insects that may have entered will starve to death, or move on in search of food. Controlling the growing environment is critical to plant health but can also help keep insects away.
The appropriate amount of heat, humidity, light, water, air circulation, and nutrients will play a large part in plant health and by extension, the plants’ ability to ward off pests. The “appropriate” levels are dictated by crop type, time of year, goals of the grower, etc., so they will not be the same year-round. These variables must be calibrated to achieve optimal plant growth in order to be an effective deterrent from attracting pest species.
Mechanical Pest Controls for Cannabis
Mechanical controls for keeping pests off your plants include those items that are meant to exclude them or trap them. Screens are often the first line of defense. They need to be in place anywhere there is a spot in the greenhouse that allows for ventilation or entry. This includes exhaust fans, roof and sidewall vents, and any doors where people come and go. After screens, the next line of defense are secondary exclusions.
Rooms within greenhouses are a great way to isolate sick plants or create microenvironments. They are, however, not very common in greenhouses and can be quite cost prohibitive to install. Row covers may be the next best thing. These are often employed in the field but can be used for indoor crops as well. These are lightweight opaque strips of fabric with varying lengths and widths. Row covers cover crops, but still allow most light and moisture to come through.
Traps are another effective mechanical control to keep pests at bay. Traps are often brightly colored sticky cards that insects fly into and get stuck. They don’t have to be brightly colored though. Some pests like thrips are attracted to blue traps, with the help of a pheromone. Traps should be placed near those same points of entry where the screens are and near the crops the pests are likely to bother. They should be placed at or just above the canopy. Be cautious about using traps with lures or attractants. In some cases, they can do more harm than good by bringing the very insects into the growing area they otherwise would not have found their way into.
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Biological Pest Control for Cannabis
Biological insect control means using either certified organic formulations of pesticides or the use of beneficial insects or other plants. When selecting organic materials for your plants, make sure they are specifically labeled for organic production. The most recognized label in North America for certified organic pesticides is the Organic Materials Review Institute’s (OMRI) seal. Products that have been reviewed and approved for organic crop production will have the OMRI initials on the outside. They are not the only third-party certifier of organic products, but they are the most visible and easiest to find. If you want to avoid any applications of insecticides, organic or not, then another strategy is to release beneficial insects.
There are numerous beneficial insects that can be introduced to your growing area. These include pest-eating predators, and those that will parasitize them. Aphids, for example, can be controlled by a healthy population of ladybug larvae who have ravenous appetites for aphids. Alternatively, the parasitic Aphidoletes will seek out aphids and lay their eggs inside of them, creating a host for their larvae who feed from the inside and emerge from their dead host. Other biological controls include the application of beneficial bacteria or fungi that are harmless to humans and plants but deadly to insect pests such as the commonly used Bacillus thuringiensis, most often sold as “Bt.”
Keeping sufficient populations of beneficial insects can be a challenge. Once they have consumed or parasitized your current pests, they either die or move on to find other prey. To ensure there are healthy populations of beneficial insects, a careful balance of keeping a certain amount of pest species by using trap crops is necessary. This is the practice of growing a sacrificial crop that attracts pest species in order to maintain sufficient populations of beneficial insects with a constant food source. It is important that the trap crop is not the same as the desirable crop or this strategy can backfire.
It should be noted that releasing beneficial insects works well in greenhouse or enclosed growing environments. It is not practical for field production of cannabis. If none of these options work to sufficiently keep bugs off your plants, then it may be time to consider chemical insecticides.
Chemical Pest Control for Cannabis
When all other options have failed, chemical pesticides may be the course of last resort to control insect infestations. The decision to use synthetic chemicals on your plants should not be taken lightly. Their use will compromise any attempt at growing organically. There are risks associated with residual pesticides on consumable products. Make sure when using chemical pesticides that only the minimum amount needed is used on the targeted plants and for the targeted species.
There are hundreds of insecticide formulations on the market. Some of them have been around for centuries, some for decades, and some have just hit the marketplace. It is important to identify the pest species you have present on your cannabis plants before selecting the appropriate pesticide. For instance, if you determine you have spider mites, there is no insecticide that will control them; you will need a miticide since spider mites aren’t technically insects.
Insects can build up resistance to synthetic pesticides. It is therefore important to not overuse them. If a problem persists, additional pesticides should be selected for the same purpose that contain a different active ingredient or different mode of action.
Pesticide labels are explicit about when, where, and how they should be used. These are not suggestions but are in fact the law. All precautions mentioned on a label must be taken including the use of personal protective equipment (PPE) and restricted entry intervals (REI) when it is safe to go into the area where pesticides were applied. In many areas, licensing must be obtained to apply pesticides, especially if they are used on any product intended for sale.
Information on licensing requirements for pesticide applicators can be found on your state or province’s website.
