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The Gras Shop - 10 / Dec / 2021

Gras Shop Blog

This article teaches gardeners and growers how to prevent and control three common plant pests, fungus gnats, spider mites, and aphids.

Gras Shop Blog
3 Common Plant Pests

Saskatchewan is home to many gardeners, growers, horticulturalists, herbalists, botanists, and naturalists who have to deal with common cannabis pests on their plants. All green thumbs know that at some point or another you’re going to have to deal with unwanted pests––spider mites, fungus gnats, and cannabis aphids ... the list goes on. 

Whether you’re a beginner or an expert, we are here to share our passion for healthy, happy plants. Here are our expert tips to identify what pests are present on your plants, how to control or get rid of pests on your plants, and how to prevent them from invading your grow operation or garden.

Fungus Gnats are a green-thumbs nightmare.

For the seasoned plant parent, identifying fungus gnats is old-hat. If this is your first time caring for a plant, don’t worry, identifying fungus gnats isn’t all that challenging. These annoying bugs look like tiny black or brown flies but with a delicate body similar to a mosquito. While adult flies are just a nuisance, their larvae can cause significant damage to your plants through the root system. The larvae feed on the roots of your plants, ultimately jeopardizing the viability of the entire root system, especially in seedlings and young plants. These weak flyers don’t stray too far from your plants, so you can find them close by or by running your finger across the soil. If you’re looking through your garden or grow site, always keep an eye out for fungus gnats.

The main cause of fungus gnats in cannabis

Fungus gnats often appear in conjunction with too much moisture, as they are attracted to decomposing plant material and wet conditions. This decomposing matter can be composed of fallen leaves, and soil additives such as wood chips, compost, and compost tea. The desire to care for and tend to our plants sometimes causes us to overwater them. Overwatering cannabis is a commonly cited reason for getting fungus gnats. The best way to prevent overwatering is by understanding the soil conditions needed for your cannabis. For many plants, including marjuana, it is important to maintain a balanced level of moisture–not too wet, nor too dry, instead just right. Understanding your plant’s needs will prevent root-rot and pests, so you can enjoy the benefits of your hard work.

Water retention is also a symptom of fungus gnat droppings. The droppings from fungus gnats inhibit your soil’s drainage. This results in your soil remaining moist and damp. This collection and retention of moisture creates fertile ground for more fungus gnats and for other pests. Fungus gnat excrement results in water retention, making your soil more fertile for fungus gnat larvae, which makes the infestation exponentially worse.


How to identify fungus gnats:



  • Adult gnats are dark brown or black in colour.


  • The larvae look like tiny white specks wiggling around on top of your plant’s soil.


Common ways to safely eradicate pests from your marijuana plants.

1. Sticky traps can help trap adult gnats

To deal with the mature gnats, you can try putting down sticky yellow cards into the soil of affected plants as well as your other plants. Gnats are attracted to the bright colour as it resembles flowers and foliage.

2. Tackle the larvae and pupa

If you want to tackle the young pests, let your soil dry completely and then use a mixture of 3% hydrogen peroxide and water at a 1:4 ratio. This helps you simultaneously water your now thirsty plants while fighting the invasive gnats.

3. Tackle gnats in your greenhouse

Gras Shop carries a number of products, like Dr. Doom’s insecticide and total release fogger, which is healthier for plants that can be sensitive to the peroxide, like many of our favourite tropicals. This product will tackle the adult gnats and is safe to use ahead of harvesting cannabis as well as in general gardening use.

4. Try a homemade spray to help with infestations

  1. Mix a half a cup of water with a half a cup of isopropyl alcohol.

  2. Add a teaspoon of dish liquid.

  3. Add mixture to spray bottle.

  4. Spray gnats where infestation and activities are most significant.

Spider Mites are a tricky pest to all cannabis growers.

Spider mites look like tiny little spiders on your cannabis. These little plant-eating-pests feed on your plants cells. They use tiny fangs to bite into your plant and feed on vital nutrients that your plant needs to grow strong and healthy. Spider mites can also eat the leaves of your cannabis. So, if you’ve found yourself wondering how to get rid of spider mites for good, use the section below, where we provide options for getting rid of spider mites, along with other helpful information like, how to tell if you have spider mites, and how to prevent spider mites. 

How to spot spider mites:


  • Your plant’s leaves will show tiny, lightly coloured specks. These specks are  bite marks left by spider mites.


  • You will notice webbing on your plants. In typical spider form, spider mites may leave webbing on your plant’s leaves.


  • If you flip your plant’s leaves over, you may see little darkly coloured dots. These tiny invaders are spider mites.


Common ways to safely get rid of spider mites on marijuana.

    1. Make a spider mite spray: Mix up a batch of homebrew spray to try to get rid of your spider mites. You can dilute 1 cup of alcohol in 30oz of water and use this as a spray to help ward off spider mites and defend your plants.

    2. Pick up a batch of professional-grade spray: Products like Doktor Doom’s Spider Mite Knockout, available here, are a great option for gardeners and growers alike. This product is safe for indoor and outdoor use, and for a large variety of different plants.

    3. Use worm castings: Otherwise known as a vermicast, worm castings are a way to enrich your soil with nutrients, and to increase its defence against, and the presence of, pests like spider mites. Incorporating a vermicast into your growing and gardening is a great step to take toward a healthier plant. Get yours here. Worm castings themselves actually have a protective effect whereby they produce a defence against plant pests and diseases.


  • Manual removal: If you are harvesting and notice spider mites,  growers will recommend not harvesting the bud of plant sections infested with spider mites. Instead, they recommend cutting off the section and hanging it upside down to dry. This allows the grower to more easily spot the spider mites for manual removal. The grower can spot the spider mites moving away from the base of the removed stem down toward the hanging tip of the plant. This allows the grower to pick off the spider mites.


Cannabis Aphids steal the nutrients your plants need.

Whether it’s aphids on plants, trees, on houseplants, in Saskatchewan or Regina, on houseplants or weed plants, those little rascals are worth keeping in check. Aphids can damage your plant’s health by feeding on your plant’s phloem. Cannabis aphids use piercing mouthparts to puncture holes in your plant and eat its most vital nutrients. This can result in your plant’s growth slowing, and in leaves wilting and yellowing.  This is why cannabis aphids are regularly described as soft-bodied insects that suck the life out of your plants. From your plant’s perspective Aphids are much less soft bodied, and bear a much greater resemblance to Bram Stoker’s Dracula. These little muther-suckers are also identifiable by their size, barely visible, their colour, white, black, brown, gray, yellow, green, and pink, and by their waxy or wooly coating. 

How to spot cannabis aphids

  1. The leaves of your plant may be producing excess sap. This also invites other issues such as black fungal moulds.

  2. Your plant may also showcase, white skin moults or a white powdery mildew on the leaves. This white substance on your cannabis leaves can lead to them drying out, yellow, becoming disfigured, and dying altogether.

  3. Slow plant growth. Because your plant’s nutrients are feeding cannabis aphids instead of your plants and its buds, and due to the stress this causes your plant, your plant’s growth can be slowed.

  4. Transmission of viral disease between plants. There are many different viral diseases that cannabis can contract and pass: Cannabis cryptic virus, Alfa mosaic virus, cucumber mosaic virus, and more. Transmission is the result of intracellular parasites, like cannabis aphids, that pass the virus from one plant to another.

  5. Honeydew: Cannabis aphids continuously excrete a sticky fluid that they leave on the surface of your plant in the form of tiny, shiny droplets, honeydew. 

Common ways to safely get rid of cannabis aphids from your marijuana plants

  1. Organic insecticides:Organic insecticides are an option to help prevent and control pests like cannabis aphids, fungus gnats, and spider mites. Essentria IC3 is an organic insecticide that might be recommended. It uses an Octopamine Blocker Technology that helps to disrupt the neurotransmitter function of plant pests. Spinosad is another commonly recommended organic insecticide. Spinosad excites pests to the point that they are too exhausted to eat. This eventually causes them to die of starvation.

  2. Beneficial Insects: Beneficial insects are a natural way to keep your plants safe from cannabis aphids and other pests. Growers and gardeners will opt to introduce insects that eat pests their plants attract. One of the major benefits of this method is that it is entirely natural, which is very attractive for many growers and gardeners.

    For more on the bugs you want and the bugs you don’t want, contact us about our bug availability—yeah, that’s right, bug availability—and about the range of products we sell to deal with plant pests.

  3. Vinegar and Water Mixture and Pruning:Another natural way to deal with cannabis aphids is through a thorough pruning of heavily infested areas and by spraying a vinegar and water mixture: Mix 1 oz of water with 3 oz vinegar, add to your sprayer and apply to infestations. Cannabis aphids find the vinegar and water mixture to be particularly troublesome, as it effectively burns them to a crisp.

Pest prevention is essential for all home-growers.

Preventing pests from ever being a problem, if at all possible, is ideal, though it may feel like a utopian pipe-dream. If you’re growing inside, you can try to seal your grow room, keeping contaminants out as best you can. Ideally, you would be only entering your growing operation after having cleaned your hands and put on your cleanest gardening clothes. As was mentioned earlier, growers and gardeners should also avoid overwatering their plants. Excessive moisture invites all the pests you’re trying to prevent. Another method for preventing your pests is by routinely checking your plants. Checking your plants for spider mites, fungus gnats, and cannabis aphids is an important growing practice. This helps with early detection, which can go a long way toward maintaining a pest-free grow operation.

With the real threat that spider mites, fungus gnats, and cannabis aphids pose to our plants, it’s important to know how to spot, prevent, and control them.

Humans are not the only ones attracted to cannabis and the other plants we love. The pests that put our plants in peril are also attracted to what our most special plants have to offer. By knowing what to look for, doing routine and regular checks, and keeping your moisture levels appropriately situated within margins, we all have a good chance to grow happy and healthy plants. If you notice an infestation or markings of pests elsewhere on your plants, like on the leaves, it’s important to take action quickly. The sooner you take control of infestations, the better off your plants will be. Finally, if you have any questions about growing or gardening, the knowledgeable staff at The Gras Shop, 511b 33rd Street, West, Saskatoon, can help.

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