Common Pests and Problems with Cannabis Plants

When you first start growing, it can be very overwhelming. There are so many factors to take into consideration. It’s exciting and scary at the same time. You’re scared of messing something up but excited about growing your own cannabis. Both the fear and excitement can cause you to do things that may cause stress to the plant. There are many common pests and problems with cannabis plants. Luckily, I am here to tell you what those things are and how to avoid them.

Common Cannabis Pests

It can be common for new growers to experience pests when growing cannabis. These common pests with cannabis can, in many cases, be prevented by keeping an ideal environment. Common pests when you’re growing cannabis include spider mites, aphids, thrips and fungus gnats. So, let me help you learn about how to identify them, how to prevent them and get rid of them.

Spider Mites

An Adult Two-Spotted Spider Mite

Identifying Spider Mites

Spider Mites & Webbing on Cannabis Plant (from

Spider mites are very tiny mites who get they name because of the webs they create. Their small size can let infestations get quite large before the grower notices, which can make them harder to get rid. You’ll usually find them on the underside of leaves. But, you’ll need a jeweler’s loupe, digital microscope or magnifying lens. In fact, it can be very difficult to spot spider mites with your naked eye. 

You’ll notice little spots on leaves. They can appear to be yellow, brown or orange. Eventually they can cause yellowing or browning of leaves. As a result, the leaves fall off prematurely. If the infestation goes on for a long time, unnoticed, you’ll start seeing their webbing on the plant. They can reproduce very quickly and an infestation can ruin a crop rather quickly. It’s vital to find them early on if you want to save your crop.

Preventing Spider Mites

Spider mites cannot reproduce in windy conditions, so having proper air circulation is important in prevention. For this reason, it’s a good idea to have a fan or fans oscillating around the room. It’s also a good idea to keep the temperature from getting too high.

You can also prevent infestations by avoiding going from outdoors (especially in gardens and other cannabis grows) directly into your grow room. You don’t want to bring any plants from outside into your grow room without treating them first. This helps to reduce chances of bringing anything into your grow area. It’s good to regularly check your leaves for anything deficiencies or pests. This can help you catch an infestation earlier.

Getting Rid of Spider Mites

It can be very tricky to get rid of spider mites because they can quickly become resistant to treatment. So, you’ll have to be persistent. For this reason, It can be beneficial to use multiple methods of treatment. Some solutions for spider mites include neem oil, alcohol, diatomaceous earth, lady bugs and other predatory mites.

Neem Oil

Neem oil is natural oil which can be used for spider mites in vegetation and early flower. You’ll need a mister to spray the plant evenly. Spray the underside of the leaves thoroughly during lights out and then make sure to have a breeze on them to help them dry before lights on. If not, the plants will burn. The oil doesn’t smell very good, so avoid spraying on buds. You should spray plants every 3 days because most insecticides don’t kill the eggs and 3 days is how long it takes the eggs to hatch. So, repeating the treatment a few times will help ensure you get them all.

There is some evidence that suggests neem oil can be harmful to humans so I’d recommend wearing gloves and even a mask while spraying.

Alcohol & Water

You can also use alcohol and water to spray your plants. Use 9 parts water and 1 part alcohol. This will kill the spider mites without causing harm to the plants. Using a mister, spray the underside of leaves during lights out. Allow the plant to dry with fans before the lights come back on. You can apply every 3 days to kill the newly hatched spider mites.

Diatomaceous Earth

You can also add diatomaceous earth to the top of the soil. This solution is harmless to humans, pets and plants. It’s very sharp on a microscopic level and will tear or dehydrate spider mites on contact. This will not get rid of the spider mites by itself but is good to use in combination with other methods to help slow down the infestation.

Predatory Insects

You can also add lady bugs or predatory mites to help control spider mites in your grow room. This can be a good option if it’s a small infestation or if you’re in flower and don’t want to spray your plants. They are natural pest control, but can be effects by other insecticides so always check the insecticides before using them if you’re using predatory bugs in your grow.

For predatory bugs in Canada, try


An Adult and Smaller Green Aphid

Identifying Aphids

Aphids on the Back of Cannabis Leaf (from

Aphids are small insects that can be green, yellow, white, brown, black and red. The adults are bigger and round or oval shaped. Where as, the nymphs are white, smaller and thinner looking. The nymphs can also be confused with thrips, so using magnification is recommended before any treatments. The adults can also be winged. These are called colonizer aphids because they fly off to start a colony on plants. The winged version still has the same body shape. They will most commonly be found on the underside of leaves and on stems. An infestation can get out of control in just a few weeks. So, again, early detection is key.

Preventing Aphids

You can prevent aphids in your indoor grow by avoiding going from outdoors (especially in the garden) directly to your grow room. This will reduce chances of bringing many common pests with cannabis into your grow. You can also add lady bugs, lady beetles or lace wings to your grow room to help prevent aphids from colonizing your plant. In fact, lady bugs can eat a large number of aphids. They won’t be able to get rid of aphids completely so they’re better used as a preventative measure, rather than a treatment.

Getting Rid of Aphids

When treating your plant for aphids, you want to try to get the numbers down quickly. Many common pests with cannabis can be treated by spraying your plants during lights out with insecticidal soap or neem oil.

Insecticidal Soap

Insecticidal soap or fatty acid salts can be very effective with treating aphids. They weaken the outer shell of the aphids, while being harmless to plants. They need to be reapplied because they only stay on the plant for a short time. It’s important to get good coverage when spraying with the soap. Even though it’s considered safe, avoid applying it on your buds. No one wants soapy buds. You’ll need to spray with this every few days to bring down numbers.

Neem Oil

Neem oil is natural oil which can be used for aphids in vegetation and early flower. You’ll need a mister to spray the plant evenly. Spray the underside of the leaves thoroughly during lights out and then make sure to have a breeze on them to help them dry before lights on. Otherwise, they will burn. The oil doesn’t smell very good, so avoid spraying on buds.


An Adult Thrip

Identifying Thrips

Leaf Damage from Thrips

Thrips look slightly different during different stages of their life. The nymphs look like white worms that don’t move. Where as, an adult thrip is a yellow, golden, transparent or brown bug that is fast moving. Thrips can also have wings depending on which stage of life they’re in. They can be found on leaves both underside and on top.

Thrips cause leaf damage that is similar to spider mites. But, the thrips spots are bigger and irregularly shaped. The spots also appear to be shiny, slimy, or silvery or bronze. The appearance has been compared to snail trails, where it’s shiny looking. If untreated, the leaves that were effected will start to die.

Preventing Thrips

You can help to prevent thrips by avoiding going directly into your grow room from outside, especially in the garden. This will reduce your chances of bringing pests into your grow.

Getting Rid of Thrips

You can get rid of thrips by spraying plants with insecticidal soap or neem oil. It is best to use these sprays during vegetation or early flower. You can use them in flower but you want to avoid spraying the buds.

You can also use predatory mites Stratiolaelaps (Hypoaspis) to help control thrips. They can be added to the soil and will eat up the thrip pupae. This will prevent them from reaching adulthood and laying more eggs.

Fungus Gnats

An Adult Fungus Gnat

Identifying Fungus Gnats

Some Dead Fungus Gnats on Cannabis Leaves (from

Fungus gnats are tiny little flying bugs. They live in the soil or medium and lay eggs in the top few inches of growing medium. They’re most commonly found in soil. They will fly right near your face when you’re in your grow room working on plants.

Preventing Fungus Gnats

You can prevent fungus gnats by using quality soil and avoid using regular garden soil. These often times have fungus gnat larva in the soil. You can also prevent fungus gnats by letting the top soil dry out between watering. In order for them to thrive, they need wet soil. You can also add a top layer of sand as this dries out faster than soil.

Getting Rid of Fungus Gnats

You can get rid of fungus gnats you can use a mixture of hydrogen peroxide and water to oxygenate the soil. This will kill larvae on contact. You can also sprinkle cinnamon on the soil to kill the fungus in the soil that the larvae are feeding on.

You can also use predatory mites, Stratiolaelaps (Hypoaspis), to control fungus gnats. These mites eat the larvae in the soil. Therefore, preventing further fungus gnats from reaching adulthood and laying more eggs. 

Cleaning Grow Room After Common Cannabis Pests 

After an infestation of ANY of the common pests with cannabis, you will need to thoroughly clean and disinfect your grow room. It is best to use a bleach and water mixture. For a more natural method, clean the dirt and dust with a solution of vinegar, water and soap. Follow up by wiping down surfaces with hydrogen peroxide. You’ll also need to clean your pots with the same solutions. Make sure to rinse well and allow to dry before using again.

Over-Watering, Under-Watering & Incorrect pH Range


Over-Watered Cannabis Plant (from

The number one mistake new growers make is over-watering their plants. We get this idea in our head that the plants need water every single day to grow. While that can be true in some cases, it’s not usually the case. If you over-saturate the soil, the plants roots cannot get oxygen, which is needed for healthy root development. The healthier the roots, the easier it is for them to do their job of absorbing nutrients and water. You want to let your growing medium dry out in between watering, so that the roots get both water and oxygen. An over-watered plant will have leaves curled downward and look very rigid because they’re full of water. Growth will slow down and if not fixed, can lead to root rot. If you over-watered your plant, let it dry out for a few days and then resume a more appropriate watering schedule.


Under-watered Cannabis Plant (from

Although more rare, some growers will underwater their plants. After hearing over-watering is the most common mistake, many new growers end up under-watering for fear of over-watering. If you have an under-watered plant, the leaves with droop and seem like they’re hanging. They may also appear thin like paper. To fix this problem is easy, just water you plant. But be sure to start with a smaller amount than usual as to not shock the plant. Once it perks up, you can give it the rest. After that, try watering more frequently.

As a seedling, plants don’t need much water, so try watering in a small circle around the stem. By doing this, rather than saturating the entire growing medium in the pot, you minimize the chance of over-watering. As the plant gets bigger, so can the circle of water. Keep enlarging the watering circle until the plant is about 8 inches tall. Once it gets to that height, water the entire medium until you see a tiny bit of run off in the tray. You can water about every other day, but monitor the top 1 inch of medium to assess the moisture in it. Once plants get bigger, so does their thirst for water.

Incorrect pH Range

Providing the correct pH range for your plant is so crucial to its health. It is one of the most common reason growers experience problems with their plants. So always check your runoff first to assess if your pH levels are correct. If the pH is not in the correct range, the plant can’t absorb all of the nutrients it needs to grow. Issues with pH levels can appear different depending on whether the pH goes lower or higher.

Different nutrients absorb at different pH values. For example in soil, nitrogen is absorbed at a pH range of about 5.5 to 7.5 but phosphorus is absorbed in the range of 6.0 to 7.0. This is why the pH for each medium has a range. Within that range, all nutrients are able to absorb through the roots. So, when you give a variety of pH to your plant, it can absorb certain nutrients more efficiently than at different times. This will help your plant to be its healthiest, which means faster growth.

Ideal pH ranges:

  • Soil – 6.0-7.0
  • Hydro/Soilless mediums – 5.5-6.5

Nutrient Burn & Nitrogen Deficiency/Toxicity

Nutrient Burn

The Early Stage of Nutrient Burn (from

Another common mistake made by first time growers is nutrient burn. This is because we want to get the best results and become a little too enthusiast with the nutrients. They either feed too much at once or too frequently. When giving plants nutrients, it’s always a better idea to start out smaller and increase it slowly. It’s much harder to get nutrient burn when using organics and living soils because you’re feeding the soil, not the roots directly. Plus, it’s a slow release of nutrients to the roots. Autoflowers require much less nutrients then photoperiod plants, so make sure not to give your autoflower a nutrient feeding designed for a photoperiod plant.

Nutrient burn will cause yellow then brown, crispy looking edges on the leaves. It will also slow down growth. The leaf tips will be affected first. So, keep your eye out for the leaf tips first. If you have nutrient burn on your plants, stop feedings for a 1-3 weeks depending on how bad the burn is and then resume a more suitable feeding schedule. This will allow the plant to flush out the large amount of nutrients.

Nitrogen Deficiency & Toxicity

Infographic (from

Nitrogen is one of three main macronutrients that cannabis plants need for proper growth. When you buy any fertilizer/nutrient, they have a N-P-K ratio on the package. These stand for: Nitrogen, Phosphorus and Potassium (K on periodic table). Nitrogen is needed most in vegetation, but important for the plant throughout its life.

If the plant doesn’t get enough nitrogen, the leaves will start to turn bright yellow and die. Towards the end of flower, this will happen naturally as the plant uses the last the nitrogen in its system. This can be easily fixed by adding some nutrients with a high N amount in the N-P-K ratio at the recommended dosage.

Nitrogen toxicity is caused by too much nitrogen in the plants system. This is also referred to as ‘the claw’ as it causes the end of the leaves to curl downward in a claw like fashion. The leaves will also turn a dark green. If you see these signs, let up on the amount of nitrogen in your nutrient feedings.

Heat Stress & Light Burn

Heat Stress

Leaves Folding from Heat Stress

Stress your plant experiences from the grow room being too hot is called heat stress. Aim to keep your temperature between 70-75°F/21°-24°C during vegetation. You can make it a little cooler every 1-2 weeks during flower to simulate fall. If it’s too hot for your plant, the leaves will fold up long ways or ‘taco’. If you suspect your plant is experiencing heat stress, try lowering the temperature. This should alleviate the symptoms of heat stress.

Light Burn

Cannabis Plant With Light Burn (from

If your plant tops are too close to your light, they will get light burn. The very tops of the plants will yellow first, and then it will spread. It can also cause pale, white bud tops if not corrected. If light burn is present, raise your light about 6 inches to 12 inches. Remember to always read your manual for your light for specifics for light height during different stages of growth. If your plant is experiencing heat stress, it is more likely to suffer from light burns.

White Powdery Mildew & Bud Rot

White Powdery Mildew

White Powdery Mildew on Leaves (from

One of the most common types of fungi your cannabis plants can get. Often caused by too much humidity in the grow room and little to no airflow. You will see a powdery substance appear on your leaves and it can spread to other plants in your grow area. It is a form of mold that can affect your cannabis plant. To get rid of it, simply spray plants with mildew eliminating spray. Also, lower humidity and increase airflow to prevent it from coming back.

Bud Rot

Plant With Bud Rot (from

Another problem caused by high humidity and poor airflow. Bud rot is exactly what it says; your buds basically rot from the inside out. The rotting is caused by another type of mold that can affect your cannabis plant. It can be very difficult to identify early on. Bud rot starts at the stem and spreads in all directions. It starts as white and wispy, then grey and black as the buds become a mushy, slimy consistency. If bud rot is present, it’s no longer safe for consumption. It needs to be removed from the plant and disposed of or the entire plant may need to dispose of. This depends on the severity of the bud rot. Prevention is the best treatment for bud rot. Maintain a constant movement of air and keep the humidity at around 50-55% to avoid issues.