Pest Management in Cannabis Cultivation

Like any other crop, cannabis plants are vulnerable to pest infestations that can damage their leaves and roots, resulting in stunted growth and a ruined harvest.

To ensure the health of their crops, cultivators need to be aware of the risks of these pests and know how to identify and deal with them. At the same time, since cannabis is intended for human consumption, cultivators must also be careful to ensure that the methods they deploy for dealing with pests do not otherwise adversely affect the quality of their cannabis.

Common cannabis pests

Ants and aphids

Ants can be a nuisance for any crop in their own right; but when an ant infestation arrives, an aphid infestation is usually not far behind.

These pests are a danger as the ants can damage the root system of the crop while aphids typically destroy the leaves of the cannabis plant. Ants also protect aphids from their natural predators, potentially making the infestation more difficult to remove when both insects are present.

To treat an infestation of ants or aphids, insecticidal soaps containing peppermint oil or orange oil can be sprayed over young, unflowering plants to act as a deterrent. If an ant hill is found, this can also be flooded with water in an attempt to encourage the ant colony to relocate.

Thrips

Due to their tiny size, a thrip infestation can be hard to detect and treat. However, if your cannabis plant leaves look brittle or have silver markings on their surface, this could indicate the presence of thrips.

Thrip populations are known to become pesticide-resistant fairly easily. However there are several trusted alternate methods for dealing with thrips at different stages of their lifecycle. For example, predatory nematodes or soil mites will destroy thrip larvae once they are hatched, while certain wasp species will feed on adult thrip populations.

Larger pests — birds and moles

Unlike the tiny thrip, birds and moles are two of the more obvious crop pests to spot. However, they can still cause significant damage to a cannabis crop if measures are not taken to limit their access to the planting space. While birds sweep in from above to steal seeds or defecate over the plant canopy, moles, and gophers can burrow underneath the crop and damage root systems as well as any irrigation systems supplying plants with water.

Birds can be deterred using netting or by placing scarecrows and/or shiny objects near the crop. A bird feeder can also be placed away from the plants, in order to encourage birds to congregate elsewhere. For moles and gophers, spraying castor oil and garlic-water mixtures over the soil may discourage them from burrowing near the cropland. Burrows can be fumigated using chemicals if found, but a good non-chemical alternative may be as simple as getting an outdoor cat.

Spotting pests with machine learning

Some pests, like birds or snails, can be easy to spot. But other pests require a much keener eye. It takes experience before a cultivator learns how to correctly link distinct leaf discoloration patterns or damage to the presence of a certain pest.

Of course, not all cultivators have the luxury of senior and experienced growers with years of experience and knowledge to tap into. Luckily for these newer or smaller operations, help is on the way.

The GrowDoc app is a mobile app specifically designed for helping diagnose nutrient deficiencies, diseases, and pest infestations in cannabis. Working in partnership with the Université de Moncton, as well as leading cannabis research institutions such as CCNB-INNOV and Colorado State University Pueblo’s Institute of Cannabis Research, the GrowDoc team has collated albums containing thousands of photos of sick plants for the app’s pattern recognition album to be trained on.

“That’s all fed together and we’ve done eight deficiencies so far, including calcium, magnesium, sulfur, nitrogen, potassium, phosphorus, and iron. And Colorado State is doing molybdenum, manganese, and boron, and they’re repeating phosphorus and potassium as well,” Daniel Lirette, founder and CEO of GrowDoc, recently told Analytical Cannabis.

The app currently features a plan health checker, a crop disease advisory segment, and a disease gallery featuring representative images for a range of different ailments.

Using just a smartphone camera, the GrowDoc app can suggest a primary diagnosis for a sick or damaged plant. A grower can then review the diagnosis and accept it, or if they do not think it is accurate, they can prompt the app to generate other suggested diagnoses that best fit the images.

As of summer 2022, when Analytical Cannabis last spoke with Lirette, the app is most advanced at identifying nutrient deficiencies. However, Lirette says that the developers are working to deliver new features in response to pest outbreaks being reported in the US and Canada.

“A new one that we’re seeing this year is the Japanese beetle,” Lirette said. “We’re seeing that on Facebook groups, but this is the first year that I’ve ever seen people on this scale have this bug. So that’s our next step: watching what’s going on in the industry, seeing what are the most common things that are happening, and adapting that way.”

Biocontrol solutions for cannabis pests

Once a pest infestation is identified, what can cannabis cultivators do to stop it in its tracks? At the federal level, there are no pesticide products approved for use on cannabis, though allowances have been made for some pesticides at the state level.

Biological pest control (biocontrol) solutions offer a pesticide-free alternative for cultivators. Instead of using chemical pesticides, biological pest control involves introducing natural predators to the environment that will deal with and prevent any harmful pest infestations.

“Biological control in cannabis, and also in all other crops, is making sure you grow your crop in a healthy way and control your threats as and when needed, with organisms that occur in the environment,” Sam Gui, an integrated pest management and pollination specialist at the Belgium-based crop management firm Biobest Group NV, previously told Analytical Cannabis.

By carefully introducing very selective predators into the cannabis crop — ones that prey on common pests but will not damage the cannabis plants — cultivators can effectively prevent troublesome infestations.

“There are groups of pests that we will find almost in every cannabis crop,” Gui explained. “Spider mites [are] one of them. There is also a series of thrip species we will find nearly in all crops. Frankliniella occidentalis is probably the most commonly found, but we find several [other] ones.”

“There is a very good one-to-one biocontrol, Phytoseiulus persimilis, which is a specialized predatory mite for spider mite control,” he continued. “’Specialized predatory mite’ means it will eat nothing else than that particular prey. So if that particular prey – if this spider mite is not present – it will rather die than switch its ‘menu’ to anything else.”

For cannabis cultivators, biocontrol solutions may be preferred over pesticides in some cases. Some cultivators judge that pesticide sprays could present too significant a risk to the environment and/or neighboring farms. Pesticide residues can also be tricky to remove from cannabis plant material, as Gui explains, and so a biocontrol alternative may reduce the amount of post-harvest processing that is needed before sale.

“It’s residue-free. So for the consumer there’s a huge benefit because if people don’t need to use chemicals, or if people can use less chemicals for growing their crops, they will not have any chemical residue in their crops, which is a health benefit for the consumer,” Gui added.

This article originally appeared in the Analytical Cannabis - June 2023 Digest.