Do you think you’ve got Cannabis Pests?

News 27 October 2021

Our guide on identifying and removing your Cannabis Pests problem naturally and for good. 

Whether you’re growing cannabis indoors or outdoors it is important to observe and monitor your plants for insects and mites, as just like any crop, cannabis has its own enemies and as a grower you will one day encounter a pest. Unfortunately, some of these pests we will go through here are known to destroy a crop relatively quickly if not found early enough. They are not always easy to spot at first, yet over time you will learn the telltale signs of pests, the damage they create, and how to properly control them.  

Quarantine 

The first step to a pest free facility is to quarantine your plants upon arrival. All plants entering a grow facility should be inspected upon receipt to determine if there are any existing pest problems. After the inspection, the plants should be quarantined for a minimum of two weeks to allow sufficient time for pest eggs to hatch out if present, as some eggs are deposited into the leaf tissue so they are difficult to detect. This space will need to be a completely separate room from other production areas.  

Monitoring 

During the quarantine stage and after, monitoring will be a grower’s most important tool. Horiver sticky cards and walk-throughs need to be counted and performed on a weekly basis. This is important for a few reasons. One, Horiver cards will allow you to observe what’s flying around or in your crop months to weeks before damage or pest pressure can be seen with the naked eye. These flying insects primarily include: thrips, whiteflies, and sciarid flies (fungus gnat/shorefly). Two, you will be able to see pest population trends. These trends will allow you to determine if your pest population is decreasing or increasing over an extended period of time. Three, weekly crop inspections will allow you to determine where hot spots are located, if they are spreading or remaining under control once biologicals have been applied. In walk-throughs you should be actively checking the soil, stems, and leaves, while performing “leaf flips”. These leaf flips are important, as most pest infestations begin to develop on the undersides of leaves.  

Pests and Biological Products - Spider Mites 

The majority of mites found in a cannabis crop are the Two Spotted Spider Mites (Tetranychus urticae). They can be easily distinguished by having two large dark spots on their back and red eyes, though they can be miss-identified due to color variation. This color variation is primarily caused by the short-day length that occurs in the flowering stage of the cannabis production cycle. This stage triggers a portion of the population to turn a red/orange/purple color as they go into diapause (hibernation).  

Spotting spider mites in a cannabis crop at first can be difficult. Infestations usually begin on plants near walls, posts or doors. Initially the damage will start off as small yellow speckles, rapidly turning into severely damaged leaves with a major amount of webbing. This can quickly kill a plant due to the lack of photosynthesis.  

 

We use two different predatory mites for the control of Spider Mites in a cannabis crop. The first being Neoseiulus californicus, found under our product name SpicalSpical is best used in the Ulti-Mite sachet form and as a PREVENTATIVE. The sachets will slowly release these predatory mites in the crop for up to four weeks. They will actively search for spider mites, migrating over plants if they are touching using the plant’s volatiles to find their prey. The plant will emit these metabolites when spider mites begin to feed on the leaves.  

The second predatory mite we use is Phytoseiulus persimilis, found under our product name Spidex Vital. Spidex Vital is best used as a CURATIVE. It comes in bulk form and is best used in diboxes when you are in the flowering stage. This way the bulk material does not get into your flower buds. In any other stage of the crop the product can be distributed as is. For later in the flowering stage when carrier is an issue, we also have Spidex Boost sachets.  These sachets are not breeder sachets, however they will instantly release 100 predatory mites into the field per sachet placement, as well as keep the crop clean from unwanted loose carrier material. Spidex will only feed on spider mites, so an active spider mite population will need to be in the crop for this predatory mite to survive.  

Phytoseiulus persimilis fighting with a Two Spotted Spider Mite

Thrips 

Thrips can be first noticed on Horiver cards well before crop damage can be found, however when actively walking your crop you will begin to see signs of stippling on the leaf surfaces, silvering on leaves from older feeding damage and black frass (fecal matter). A secondary reason to remove thrips from your grow room is the indirect damage they can cause by acting as vectors, potentially transmitting viruses between plants. Most thrips found in cannabis crops are common thrips species, like the Western Flower Thrips (Frankliniella occidentalis) and the Onion Thrips (Thrips tabaci). These thrips will be a yellowish-brown in color and averaging a length of 0.8-1.2mm long.  

Onion thrips or Thrips tabaci

It is often necessary to have to use multiple biological controls to decrease thrips pest pressure so that multiple stages of the pest life cycle is targeted at the same time. Amblyseiulus swirskii or our Swirski Ulti-Mite product is used when growers want to treat PREVENTATIVELY or CURATIVELY, however predatory mites will only feed on 1st instar thrips larva and eggs. That is why they are best used in conjunction with other products including; Thripor and EntomiteThripor is the predatory bug Orius insidious. It is considered a generalist predator with the preference for all active life stages of thrips. It will react to any movement rapidly, piercing the thrips body with its mouthparts, consuming it whole. The third and final product that can be used is our Entomite product. It is the soil-dwelling predatory mite Stratiolaelaps scimitus. This predatory mite will feed on the thrips pupa that pupate in the soil. With all three actively working together in a cannabis crop, your thrips pressure will decrease rapidly over time.  

Thripor feeding on thrips larva

Sciarid Flies (Fungus Gnats) 

Adult Fungus Gnats can be a nuisance and are easily spotted in the crop when working in your growing medium. They are roughly 1-5mm long, are greyish-black, and have a long antenna. Fungus Gnat adults do not typically cause direct plant damage, although they can become a contaminant of the final product when they get stuck to resin glands. The Laval stage however will feed directly on the roots of the plant. Larva can be identified in the soil by their brownish-black head capsule. They will also be cylindrical, milky white to opaque, and have 12 body segments. 

Sciarid Fly

Multiple biological products can be used to treat this pest. Initially, we always suggest placing yellow Horiver cards near the soil line, as these cards will capture mass amounts of sciarid fly adults. Removing adults from your crop will decrease the number of eggs laid, reducing the development of larva. The larva then can be treated with the soil dwelling predatory mite talked about above - Stratiolaelaps scimitus (Entomite). If you notice a large influx of sciarid fly larva you can also treat with the product Entonem (Steinernema feltiae). Entonem is a nematode that will lay inactive in the soil when applied until a sciarid fly larva wiggles by. It will then attack, ambushing its prey. Entonem is known to work best when applied with Entomite.  

Entomite

Root Aphids/Cannabis Aphids 

Aphids will be one of the most difficult pests a cannabis grower experiences. Due to their short generation time and rapid reproduction rate an aphid population can reach serious levels promptly. Each aphid will begin extracting plant sap, secreting honeydew and possibly introducing toxic substances to your crop, as soon as they are born.  

 

Cannabis Aphid

Biologicals have been found to work well at controlling Cannabis Aphids, however it is very difficult to eliminate them completely so the most important control measure is preventing them from entering your crop initially. All facilities should be screened to prevent the entrance of aphids and all measures to ensure workers do not bring in or transfer aphids from one room to another must be taken. If Aphids are found they will need to be identified to ensure proper corrective action and then it is best to remove all infested material.  

 

For Cannabis Aphids we have found that Aphipar-M and Chrysopa provide the highest level of control. You can use these products both as a PREVENTATIVE or CURATIVE application. All products will need to be applied every seven days until no aphids are found in the crop. Aphipar-M is a parasitic wasps (Aphidius matricariae). It works by parasitizing (laying eggs inside) live aphids. Once the aphid is parasitized, they will slowly die and turn into a greyish-brown, leathery mummy. The parasitic wasp inside the mummy will hatch roughly two-three weeks after it has been parasitized. This cycle routinely occurs, slowly removing aphids from the  crop. Chrysopa or Chrysoperla carnea works an entirely different way, known by the nickname “Aphid Lions”. They will search for their prey randomly, consuming their kill by grasping them from below, injecting them with a salivary fluid that digests the pests body content, which is then sucked out by the lion.  

Chrysopa feeding on a Aphid sp.

For Root Aphids, we have not been able to find a biological control product yet that will adequately dominate a pest population although many do have some effect. If you have a root aphid infestation and do not want it to spread or would like to ensure one does not develop it is best to preventatively wrap the block, slab or pot with a fabric that has a tight enough weave to prevent aphids from escaping or entering the soil (Reemay is a common brand). This should be done on all plants in all stages of the crop. Then curatively treat by spraying insecticidal soap and registered entomopathogenic fungi, every 4-7 days.  

Root Aphid

Other Pests 

There are a few other pests that are known to appear in Cannabis crops, however they are usually unlikely to cause an issue, especially if you’re already treating preventatively for thrips and spider mites. These pests include broad mites, hemp russet mites and whiteflies. Most generalist predatory mites (Amblyseiulus swirskii and Neoseiulus californicus) will take care of this situation, as they feed on all different types of pests.  

 

Conclusively, a blowout of insects in your cannabis crop can be avoided by following the techniques explained above. Actively quarantining your plants, monitoring your rooms, and treating preventatively with bio-controls is a must to not be surprised with a major pest infestation.  

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